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\DOI{10.5802/crchim.447}
\datereceived{2025-11-06}
\daterevised{2026-02-07}
\datererevised{2026-02-18}
\dateaccepted{2026-02-26}
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\COI{The authors do not work for, advise, own shares in, or receive
funds from any organization that could benefit from this article, and
have declared no affiliations other than their research organization.}

\begin{document}

%\dateposted{2026-02-16}

\begin{noXML}

\CDRsetmeta{articletype}{research-article}

\title{Metal-free synthesis of 4-(methylthio)-3-phenylisoquinolines}

\alttitle{Synth\`{e}se sans m\'{e}tal de
4-(m\'{e}thylthio)-3-ph\'{e}nylisochinolines}

\author{\firstname{Chengqun} \lastname{Chen}\IsCorresp}  
\address{Department of Chemical Engineering, Fuzhou University Zhicheng
College, Fuzhou, PR China}                      
\email[C. Chen]{chenchq03@yeah.net}

\author{\firstname{Xiaosheng} \lastname{Xie}}  
\addressSameAs{1}{Department of Chemical Engineering, Fuzhou University
Zhicheng College, Fuzhou, PR China}                            

\thanks{Fuzhou University Zhicheng College Students' Innovation and
Entrepreneurship Training Program (2025045)}

\keywords{\kwd{Tetrafluoroborate}\kwd{Azide}\kwd{Isoquinoline}\kwd{Methylthio}\kwd{Synthesis}}

\altkeywords{\kwd{T\'{e}trafluoroborate}\kwd{Azide}\kwd{Isoquinol\'{e}ine}\kwd{M\'{e}thylthio}\kwd{Synth\`{e}se}}

\begin{abstract}
Herein, we report a straightforward protocol for synthesizing
4-(methylthio)-3-phenyliso\-quinolines, which are valuable compounds in
medicinal chemistry for their biological activities. This method uses
1-(azidomethyl)-2-(phenylethynyl)benzenes and
dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTSM) under
mild, metal-free conditions. Notably, it tolerates diverse aromatic
functional groups, enabling derivative preparation. The reaction
proceeds smoothly, affording products in good to excellent yields. By
avoiding hazardous and malodorous methylthio radical reagents as well
as methylthio nucleophile precursors, this protocol provides a
practical and eco-friendly route to sulfur-containing heterocycles.
\vspace*{-2pt}
\end{abstract}

\begin{altabstract}
Ici, nous pr\'{e}sentons un protocole simple pour la
synth\`{e}se de 4-(m\'{e}thylthio)-3-ph\'{e}nylisochinolines,
compos\'{e}s pr\'{e}cieux en chimie m\'{e}dicinale pour leurs
activit\'{e}s biologiques. Cette m\'{e}thode utilise des
1-(azidom\'{e}thyl)-2-(ph\'{e}nyl\'{e}thynyl)benz\`{e}nes et du
trifluorom\'{e}thanesulfonate de dim\'{e}thyl(m\'{e}thylthio)sulfonium
(DMTSM) dans des conditions douces et sans m\'{e}tal. Notamment, elle
tol\`{e}re divers groupes fonctionnels aromatiques, permettant la
pr\'{e}paration de d\'{e}riv\'{e}s. La r\'{e}action progresse
facilement, donnant des produits avec des rendements bons \`{a}
excellents. En \'{e}vitant les r\'{e}actifs \`{a} radical
m\'{e}thylthio dangereux et malodorants ainsi que les pr\'{e}curseurs
nucl\'{e}ophiles m\'{e}thylthio, ce protocole offre une voie pratique
et \'{e}cologique pour obtenir des h\'{e}t\'{e}rocycles soufr\'{e}s.
\end{altabstract}

%\input{CR-pagedemetas}

\maketitle

\vspace*{-1pt}

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\end{noXML}

\section{Introduction}\label{sec1}

Isoquinolines, an important class of nitrogen heterocycles, exhibit
diverse bioactivities and are widely present in natural products, such
as isoquinoline alkaloids as key examples. As a ubiquitous motif, the
isoquinoline scaffold possesses a bicyclic architecture, found in the
secondary metabolites of plants (e.g., aforementioned alkaloids) and
microbial natural products. Notably, these molecules show remarkable
bioactivities, e.g., anti-inflammatory, antispasmodic, antiallergic,
anticancer~\cite{1,2,3,4,5,6}.

Alkyne annulation of nitrogen-containing arenes via C--H/N--H
functionalization enables the installation of vicinal C--N and C--C
bonds across an alkyne in a single transformation. This approach has
emerged as a powerful tactic for step-economical assembly of diverse
heterocycles, which exhibit activities relevant to medicinal chemistry
and biology~\cite{7,8,9}. As an illustration, the Larock group reported
that a broad range of 3,4-disubstituted isoquinolines can be
synthesized via Pd-catalyzed annulation of alkynes (or allenes) with
aldehydes and \textit{tert}-butylamine~\cite{10,11,12,13,14,15}.
Additionally, 2-alkynylbenzyl azides serve as suitable substrates for
synthesizing isoquinoline derivatives~\cite{16,17,18,19}. For instance,
Li et~al.~\cite{16} described a PdI\tsub{2}/I\tsub{2}-catalyzed
thiolation-annulation route involving alkynes, azides, and disulfides
for the synthesis of 4-sulfenylisoquinolines. Separately, the Liang
group~\cite{17} and the Yamamoto group~\cite{18} independently reported
the Ag- or Au/Ag-catalyzed cyclization of 2-alkynylbenzyl azides, which
affords 1,3-disubstituted isoquinolines.

Metal-free strategies have further expanded the utility of
2-alkynylbenzyl azides, particularly under mild conditions.
Visible-light-promoted selenylation/cyclization of 2-alkynylbenzyl
azides with selenosulfonates produces 4-selenoisoquinolines in up to
83\% yield using AcOH as the solvent and 50 W white LEDs,
simultaneously forming C(sp\tsup{2})--Se and C--N bonds~\cite{20}.

Nevertheless, the prevailing approaches to produce sulfur-containing
groups still depend heavily on hazardous, malodorous
reagents---including thiols and disulfides. As an electrophilic
methylthiolating reagent, dimethyl(methylthio)sulfonium
trifluoromethanesulfonate (DMTSM) is particularly notable, featuring
unique advantages including safety, good crystallinity, and convenient
handling~\cite{21,22,23}. In recent years, the application of
dimethyl(methylthio)sulfonium salts in organic synthesis has garnered
significant attention, with their utility in direct
alkylthiolation~\cite{24}, cycloaddition~\cite{25,26,27},  and C--C
bond formation reactions~\cite{28} being extensively investigated. Over
the past few years, the Xie group has reported a series of outstanding
studies in the fields of alkene hydrofunctionalization~\cite{29},
direct addition reactions of terminal alkyl alkynes~\cite{30}, and
intermolecular alkene arylsulfenylation via episulfonium ion
intermediates using DMTSM~\cite{31,32,33}. Building on this body of
research, we herein report a novel and practical method for the
synthesis of substituted 4-(methylthio)-3-phenylisoquinolines using
DMTSM as a key component under ambient temperature conditions
(Scheme~\ref{sch1}).

\begin{scheme*}
\includegraphics{sc01}
\vspace*{6pt}
\caption{\label{sch1}Synthesis of
4-(methylthio)-3-phenylisoquinolines.}
\vspace*{-4pt}
\end{scheme*}

\section{Results and discussion}\label{sec2}

The initial study was initiated by adding
1-(azidomethyl)-2-(phenylethynyl)benzene and
dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTSM) to
acetonitrile. Subsequently, the resulting substrate mixture was stirred
at ambient temperature under an air atmosphere. After 12 h of reaction,
the target compound, 1-(azidomethyl)-2-(phenylethynyl)benzene
(\textbf{3a}), was successfully synthesized in a 21\% yield. To improve
the yield of this transformation, the effects of solvents, reaction
temperature, bases, and catalysts were systematically investigated
(Table~\ref{tab1}).

%tab1
\begin{table*}
\caption{\label{tab1}Optimization of reaction
conditions$^{\mathrm{a}}$
\tpar{\protect\inlinefig{fx01}}\vspace*{-12pt}}
\tabcolsep4pt
\begin{tabular}{cccccccccc}
\thead
Entry & Solvent & Temp (\textdegree C) & \parbox[t]{3.5pc}{\centering Base (1.5~equiv)}\vspace*{2pt} & Yield (\%)$^{\mathrm{b}}$ & 
Entry & Solvent & Temp (\textdegree C) & \parbox[t]{3.5pc}{\centering Base (1.5~equiv)} & Yield (\%)$^{\mathrm{b}}$ \\
\endthead
1 & MeCN & rt & None & 21 & 8 & CH\tsub{2}Cl\tsub{2} & 70 & None & 11 \\ 
2 & CH\tsub{2}Cl\tsub{2} & rt & None & 32 & 9 & CH\tsub{2}Cl\tsub{2} & rt & AcONa & 60 \\ 
3 & DCE & rt & None & 26 & 10 & CH\tsub{2}Cl\tsub{2} & rt & $t$-BuOK & 15 \\ 
4 & THF & rt & None & 11 & \textbf{11} & \textbf{CH}\tsub{2}\textbf{Cl}\tsub{2} & \textbf{rt} & \textbf{K}\tsub{2}\textbf{CO}\tsub{3} & \textbf{77} \\ 
5 & Dioxane & rt & None & 7 & 12$^{\mathrm{c}}$ & CH\tsub{2}Cl\tsub{2} & rt & K\tsub{2}CO\tsub{3} & 72 \\ 
6 & CH\tsub{2}Cl\tsub{2} & 40 & None & 34 & 13$^{\mathrm{d}}$ & CH\tsub{2}Cl\tsub{2} & rt & K\tsub{2}CO\tsub{3} & 70 \\ 
7 & CH\tsub{2}Cl\tsub{2} & 55 & None & 29 & 14$^{\mathrm{e}}$ & CH\tsub{2}Cl\tsub{2} & rt & K\tsub{2}CO\tsub{3} & 71
\botline
\end{tabular}
\tabnote{$^{\mathrm{a}}$Reaction conditions: \textbf{1a} (0.5 mmol), \textbf{DMTSM} (0.6 mmol), base (0.75 mmol), and solvent (2 mL) under air for 12 h.}
\tabnote{$^{\mathrm{b}}$Isolated yields.}
\tabnote{$^{\mathrm{c}}$CuI (0.05 mmol) was added as the catalyst.}
\tabnote{$^{\mathrm{d}}$Cu(OAc)\tsub{2} (0.05 mmol) was added as the catalyst.}
\tabnote{$^{\mathrm{e}}$FeCl\tsub{3} (0.05 mmol) was added as the catalyst.}
\tabnote{CH\tsub{2}Cl\tsub{2} ${=}$\ dichloromethane, DCE ${=}$\ dichloroethane, THF ${=}$\ tetrahydrofuran.}
\vspace*{-2pt}
\end{table*}

An initial solvent screening was conducted, evaluating dichloromethane
(CH\tsub{2}Cl\tsub{2}), dioxane, 1,2-dichloroethane (DCE), and
tetrahydrofuran (THF) as reaction media (Table~\ref{tab1}, entries
2--5). The reactions were conducted at room temperature without the
addition of an external base. Notably, dichloromethane
(CH\tsub{2}Cl\tsub{2}) proved to be the optimal solvent, affording the
desired product in 32\% yield---outperforming all other tested
solvents. Specifically, 1,2-dichloroethane (DCE) gave a yield of 26\%,
whereas the polar aprotic solvents tetrahydrofuran (THF) and dioxane
resulted in substantially lower yields at 11\% and 7\%, respectively.
These results underscore the superior performance of
CH\tsub{2}Cl\tsub{2} in promoting this transformation relative to the
other evaluated solvents. Furthermore, elevating the reaction
temperature was found to be detrimental to the product yield
(Table~\ref{tab1}, entries 6--8). Various bases were tested to
accelerate the reaction (Table~\ref{tab1}, entries 9--11), It was found
that K\tsub{2}CO\tsub{3} yields better results than AcONa and $t$-BuOK.
This outcome was primarily attributed to the degradation of DMTSM by
the strong base. Meanwhile, catalysts including CuI, Cu(OAc)\tsub{2},
and FeCl\tsub{3} exerted no significant effect on the reaction
(Table~\ref{tab1}, entries 12--14). Consequently, an optimized yield of
77\% was achieved by using DMTSM (1.2 equiv) under the reaction
conditions specified in Table~\ref{tab1}, entry 11:
CH\tsub{2}Cl\tsub{2} as the solvent at rt, K\tsub{2}CO\tsub{3} (1.5
equiv) for 12~h.

The scope of the reaction was then evaluated and various
1-(azidomethyl)-2-(phenylethynyl)benzene derivatives, bearing different
groups, were treated with DMTSM(1.2 equiv), affording the
4-(methylthio)-3-phenylisoquinolines in various yields
(Table~\ref{tab2}). Generally, when R\tsup{2} was a
para-alkyl-substituted phenyl group (Alkyl ${=}$\ Me-, Et-, and
\mbox{$t$-Bu-)}, the target products \textbf{3b--3d} were obtained in
good yields. A slight decrease in the yield was observed when the
methyl group was at the \textit{meta} or \textit{ortho} position of the
aromatic ring; yields of only 69\% and 67\% were obtained, respectively
(\textbf{3e,3f}). An 83\% yield was obtained when the methoxy group was
at the \textit{para} position of the aromatic ring, and a 76\% yield
was reached with the methoxy group at the \textit{meta} position. When
R\tsup{2} was 3,4,5-trimethoxyphenyl, an excellent yield (81\%) was
still attained, demonstrating the favorable electron-donating effect of
methoxy groups (\textbf{3g--3i}). However, when R\tsup{2} was a halogen
at the \textit{para} position on the aryl group, the yield decreased
significantly; in contrast, a good yield was still obtained when
R\tsup{2} was a biphenyl group (\textbf{3j--3m}). When R\tsup{2} was a
heterocyclic group or an alkyl group, the yields of all corresponding
products were less than 60\% (\textbf{3n--3r}).

%tab2
\begin{table*}
\caption{\label{tab2}Scope of 1-(azidomethyl)-2-(phenylethynyl)benzene
olefinations\vspace*{4pt}\tpar{\protect\inlinefig{fx02}}\vspace*{-9pt}}
\begin{tabular}{c}
\tbody
\protect\xxinlinefig{fx03}
\botline
\end{tabular}
\end{table*}

As expected, when the R\tsup{1} group of substrates \textbf{1} was
replaced by one or two methyl groups, the \mbox{corresponding} cyclized
products \textbf{3s--3v} were also isolated in excellent yields.
Similarly, when R\tsup{1} was an electron-withdrawing group, the
cyclized products \textbf{3} were still obtained in good yields
(\textbf{3w--3y}, yield up to 79\%). While a methoxy group at the
R\tsup{1} position also afforded excellent yields, it did not lead to
any further increase in the yield (\textbf{3z}, 83\%). 

To gain insights into the reaction mechanism, a series of control
experiments were performed. First, butylated hydroxytoluene (BHT) and
2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) were employed as radical
inhibitors of the reaction (Scheme~\ref{sch2}, Equations (1) and (2)), and no
significant impact on the isolated yield was observed. Upon
substituting DMTSM with CH\tsub{3}SSCH\tsub{3} in the presence of
I\tsub{2}, product \textbf{3a} could still be formed, yet the yield was
merely 38\% (Scheme~\ref{sch2}, Equation (3)).

\begin{scheme*}
\vspace*{4pt}
\includegraphics{sc02}
\vspace*{8pt}
\caption{\label{sch2}Control experiments.}
\end{scheme*}

Based on these results and the literature~\cite{16,20}, a reaction
mechanism (Scheme~\ref{sch3}) was proposed as follows: the sulfonium group transfer from
DMTSM to 2-styrylbenzoic acid generates the intermediate episulfonium
ion (\textbf{I}); subsequently, the formation of the cyclic
intermediate (\textbf{II}) is achieved through intramolecular
cyclization; ultimately, the anticipated product is generated when the
cyclic intermediate (\textbf{II}) experiences the concomitant processes
of deprotonation and N\tsub{2} elimination.

\begin{scheme*}
\includegraphics{sc03}
\vspace*{8pt}
\caption{\label{sch3}Proposed mechanism.}
\vspace*{-2pt}
\end{scheme*}

\section{Conclusion}\label{sec3}

In conclusion, we herein report a straightforward and efficient
protocol for the synthesis of 4-(methylthio)-3-phenylisoquinolines.
This protocol involves the {reaction} of
1-(azidomethyl)-2-(phenylethynyl)benzene with
dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSM) under mild,
metal-free conditions, and exhibits good tolerance toward a diverse
range of functional groups on the aromatic ring, thus affording the
corresponding products in good to excellent yields.

\section{Experimental part}\label{sec4}
\subsection{General information}\label{ssec41}

All reagents were purchased from Aladdin, Macklin, or Merck and
directly used without further \mbox{purification.} Column chromatography
separations were carried out on silica gel (200--300 mesh). 

NMR spectra were performed on a Bruker 400MHz (\tsup{1}H: 400 MHz;
\tsup{13}C: 100 MHz; \tsup{19}F: 376 MHz) spectrometer, using
CDCl\tsub{3} as a solvent and TMS as the internal standard. Melting
points are uncorrected. The NMR results were processed using the
MestReNova program. HRMS was carried out on a high-resolution mass
spectrometer (LCMS-IT-TOF) by Agilent 7890 LECO PEGASUS\break HRT 4D.

\vspace*{2pt}

\subsection{Experimental procedures}\label{ssec42}

\vspace*{2pt}

\subsubsection{General procedure for the synthesis of DMTSM~\cite{30}}

\vspace*{2pt}

\inlinefig{fx04}

\vspace*{2pt}

At 0~\textdegree C (ice bath), to a solution of methyl
trifluoromethanesulfonate (12 mmol, 1.36 mL, 1.2 equiv) in
CH\tsub{2}Cl\tsub{2} (10 mL), Me\tsub{2}S\tsub{2} (10 mmol, 0.89 mL,
1.0~equiv) was added dropwise in 30 min. The mixture was stirred for 
1~h at that temperature, followed by 18~h at room temperature. Upon
completion, the resulting white solid was collected by filtration and
washed with fresh distilled Et\tsub{2}O under nitrogen atmosphere,
affording dimethyl(methylthio)sulfonium trifluoromethanesulfonate 
(2.27~g, 88\% yield) as a white solid.

\vspace*{2pt}

\subsubsection{Synthesis of 1-(azidomethyl)-2-(phenylethynyl){\ubreak}benzene~\cite{20}}

\vspace*{2pt}

\inlinefig{fx05}

\vspace*{2pt}

Pd(PPh\tsub{3})\tsub{2}Cl\tsub{2} (0.03 mmol, 1 mol\%) and CuI 
(0.06~mmol, 2 mol\%) were sequentially added to a stirred solution of
phenylacetylene (3.6~mmol, 1.2~equiv) in Et\tsub{3}N (10 mL) under an
argon atmosphere at rt. The mixture was stirred for 10 min. Then
(2-iodophenyl)methanol (3.0 mmol, 1.0 equiv) was added. The mixture was
stirred overnight. An aqueous saturated solution of NH\tsub{4}Cl (8 mL)
was added to the resulting mixture, and the mixture was extracted with
EtOAc (2 ${\times}$ 10 mL). The organic layers were combined to be
washed with brine and dried over Na\tsub{2}SO\tsub{4} for 20 min. The
solution was then concentrated under reduced pressure. The obtained
residue was further purified by flash column chromatography on silica
gel to give (2-(phenylethynyl)phenyl){\ubreak}methanol.

DBU (1.3 mmol, 1.3 equiv) and diphenyl phosphoryl azide (DPPA, 1.2
mmol, 1.2 equiv) were sequentially added portionwise to a solution of
(2-(phenylethynyl)phenyl)methanol (1.0 mmol, 1.0~equiv) in toluene (2
mL) at rt. The mixture was stirred overnight. After completion of the
reaction, determined by TLC analysis, the reaction mixture was
extracted with EtOAc (2 ${\times}$ 5 mL). The organic layers were
combined, then washed with brine and dried over Na\tsub{2}SO\tsub{4}
for 20 min. The solution was concentrated under reduced pressure. The
obtained residue was further purified by flash column chromatography on
silica gel to give pale yellow oil
1-(azidomethyl)-2-(phenylethynyl)-{\ubreak}benzene.

Other compounds \textbf{1} were synthesized according to the above
procedures.

\subsubsection{General procedure for the synthesis of 
4-(methylthio)-3-phenylisoquinolines}

\vspace*{2pt}

\inlinefig{fx06}

To a solution of 1-(azidomethyl)-2-(phenylethynyl)benzene (0.5 mmol, 1
equiv) at rt in CH\tsub{2}Cl\tsub{2} (2 mL), DMTSM (0.6 mmol, 1.2
equiv) and K\tsub{2}CO\tsub{3} (0.75 mmol, 1.5 equiv) were added to the
solvent. The mixture was stirred for 12 h (TLC-monitored). The reaction
mixture was extracted with CH\tsub{2}Cl\tsub{2} after adding the
saturated brine. Then the organic phases were combined and dried with
anhydrous Na\tsub{2}SO\tsub{4}. The solvent was evaporated in vacuo,
the crude product was purified by column chromatography on silica gel,
eluting with petroleum ether/EtOAc to afford the desired products.

\subsection{Characterization data of products}\label{ssec43}
\subsubsection{4-(Methylthio)-3-phenylisoquinoline (3a)}

\inlinefig{fx07}

Brown solid (97 mg, 77\%); mp ${=}$\ 129--132~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):
$\delta=9.32$ (s, 1H),
8.29 (d, $J=7.5$ Hz, 1H), 8.24 (dd, $J=8.8$, 3.2 Hz, 2H), 
8.07 (d, $J=7.4$ Hz, 1H), 7.80 (dd, $J=6.8$, 1.2 Hz, 1H), 
7.65--7.58 (m, 3H), 7.57--7.52 (m, 1H), 2.79 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=155.9$, 146.8, 139.6, 138.8, 130.0, 129.2, 129.1, 128.6
(2C), 127.4 (2C), 127.1, 125.9, 124.6, 120.8, 18.9; 
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{16}H\tsub{14}NS$^{+}$: 252.0841, found: 252.0841.

\subsubsection{4-(Methylthio)-3-(p-tolyl)isoquinoline (3b)}

\inlinefig{fx08}

Brown solid (103 mg, 78\%); mp ${=}$\ 125--128~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.27$
(s, 1H), 8.10 (d, $J=8.0$ Hz, 1H), 7.98  (d, $J=8.3$ Hz, 2H), 7.90 (dd,
$J=7.8$, 1.6 Hz, 1H),  7.65--7.60 (m, 1H), 7.47--7.42 (m, 1H),  7.24
(d, $J=8.3$ Hz, 2H), 2.59 (s, 3H), 2.35 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=158.5$, 150.2, 144.7, 139.2, 135.0, 130.0, 129.4 (2C), 129.2,
127.3 (2C), 127.1, 125.8, 124.5, 121.1, 23.2, 19.0; \textbf{HRMS (ESI)}
($m/z$): [M${+}$H]$^{+}$ calcd. for C\tsub{17}H\tsub{16}NS$^{+}$:
266.0998, found: 266.0996.

\subsubsection{3-(4-Ethylphenyl)-4-(methylthio)isoquinoline (3c)}

\inlinefig{fx09}

Pale yellow solid (110 mg, 79\%); mp ${=}$\ 130--132~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.41$
(s, 1H), 8.22 (d, $J=5.2$ Hz, 1H), 8.12 (d, $J=7.6$ Hz, 2H),  7.91 (d,
$J=4.8$ Hz, 1H), 7.77--7.72 (m, 1H), 7.58--7.53 (m, 1H), 7.39 (t,
$J=7.6$ Hz, 2H), 2.76--2.69 (m, 5H),  1.29 (t, $J=7.2$ Hz, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=157.4$, 148.5, 145.1, 144.2, 136.0, 129.6, 128.7, 127.8 (2C),
127.0 (2C), 126.6, 125.3, 124.2, 120.6, 28.2, 17.1, 15.1; \textbf{HRMS
(ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{18}H\tsub{18}NS$^{+}$: 280.1154, found: 280.1153.

\vspace*{2pt}

\subsubsection{3-(4-(\textit{tert}-Butyl)phenyl)-4-(methylthio){\ubreak}isoquinoline
(3d)}

\vspace*{2pt}

\inlinefig{fx10}

White solid (117 mg, 76\%); mp ${=}$\ 138--140~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.34$
(s, 1H), 8.13 (d, $J=7.2$ Hz, 1H), 8.03  (d, $J=8.4$ Hz, 2H), 7.76 (d,
$J=6.0$ Hz, 1H), 7.68--7.63 (m, 1H), 7.50--7.45 (m, 1H), 7.34 (t,
$J=8.4$ Hz, 2H), 2.70 (s, 3H), 1.40 (s, 9H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=156.3$, 150.4, 149.5, 144.9, 136.7, 130.4, 129.5, 127.7 (2C),
127.4 (2C), 127.1, 126.0, 124.8, 121.0, 32.3, 24.1 (3C), 18.0;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{20}H\tsub{22}NS$^{+}$: 308.1467, found: 308.1468.

\vspace*{2pt}

\subsubsection{4-(Methylthio)-3-(m-tolyl)isoquinoline (3e)}

\vspace*{2pt}

\inlinefig{fx11}

Yellow solid (89 mg, 67\%); mp ${=}$\ 124--126~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.35$
(s, 1H), 8.18 (d, $J=6.4$ Hz, 1H), 8.01--7.97 (m, 2H), 7.78 (d, 
$J=5.4$~Hz, 1H), 7.71--7.68 (m, 1H), 7.56--7.51 (m, 1H), 7.42--7.37 (m, 1H),
7.26 (d, $J=8.4$ Hz, 1H), 2.80 (s, 3H), 2.47 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100~MHz, CDCl\tsub{3}):
$\delta=159.1$, 149.9, 146.1, 137.6, 137.0, 130.6, 130.4, 129.8, 129.1,
128.7, 127.7, 126.4, 125.1, 124.0, 121.1, 22.0, 18.4; \textbf{HRMS
(ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{17}H\tsub{16}NS$^{+}$: 266.0998, found: 266.0999.

\vspace*{2pt}

\subsubsection{4-(Methylthio)-3-(o-tolyl)isoquinoline (3f)}

\vspace*{2pt}

\inlinefig{fx12}

Brown solid (91 mg, 69\%); mp ${=}$\ 131--133~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.30$
(s, 1H), 8.16 (d, $J=7.2$ Hz, 1H), 7.90 (d, $J=8.4$ Hz, 1H), 7.74--7.69
(m, 1H), 7.59--7.54 (m, 1H), 7.48--7.44 (m, 1H), 7.34--7.26 (m, 3H),
2.68 (s, 3H), 2.30(s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100~MHz, CDCl\tsub{3}): 
$\delta=160.4$, 149.0, 145.8, 142.2, 136.4, 131.7, 131.0, 130.5, 130.3,
129.4, 127.8, 127.1, 126.9, 125.6, 125.1, 19.8, 17.5;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{17}H\tsub{16}NS$^{+}$: 266.0998, found: 266.1000.

\subsubsection{3-(4-Methoxyphenyl)-4-(methylthio){\ubreak}isoquinoline (3g)}

\vspace*{6pt}

\inlinefig{fx13}

White solid (117 mg, 83\%); mp ${=}$\ 126--129~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.21$
(s, 1H), 8.16--8.09 (m, 3H), 7.82 (t, $J=4.4$ Hz, 1H),  7.71--7.66 (m,
1H), 7.52--7.47 (m, 1H), 7.03 (d, $J=7.2$ Hz, 2H), 3.82 (s, 3H),
2.68(s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=163.1$, 158.9, 151.1, 144.1, 133.5, 131.2, 130.5, 130.1 (2C),
128.2, 126.9, 124.8, 122.4, 114.1 (2C), 55.4, 18.4; \textbf{HRMS (ESI)}
($m/z$): [M${+}$H]$^{+}$ calcd. for C\tsub{17}{H}\tsub{16}NOS$^{+}$:
282.0947, found: 282.0949.

\subsubsection{3-(3-Methoxyphenyl)-4-(methylthio){\ubreak}isoquinoline (3h)}

\vspace*{6pt}

\inlinefig{fx14}

Pale yellow solid (107 mg, 76\%); mp ${=}$\ 122--124~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.20$
(s, 1H), 8.19 (d, $J=7.2$ Hz, 1H), 7.74 (d, $J=8.4$ Hz, 1H), 7.73--7.65
(m, 3H), 7.55--7.50 (m, 1H), 7.43--7.38 (m, 1H), 7.05 (dd, $J=$ 7.0,
3.2 Hz, 1H), 3.91 (s, 3H), 2.57 (s, 3H); \tsup{\textbf{13}}\textbf{C
NMR} (100 MHz, CDCl\tsub{3}):  $\delta=161.9$, 156.6, 147.8, 144.2,
141.1, 130.7, 130.3, 129.9, 129.0, 126.6, 123.1, 120.5, 120.4, 115.9,
112.3, 54.2, 19.6; \textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd.
for C\tsub{17}H\tsub{16}NOS$^{+}$: 282.0947, found: 282.0944.

\subsubsection{4-(Methylthio)-3-(3,4,5-trimethoxyphenyl){\ubreak}isoquinoline
(3i)}

\inlinefig{fx15}

White solid (138 mg, 81\%); mp ${=}$\ 136--139~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.29$
(s, 1H), 8.19 (d, $J=7.6$ Hz, 1H), 7.83 (d, $J=7.4$ Hz, 1H), 7.75--7.70
(m, 1H), 7.58--7.53 (m, 1H), 7.36 (s, 2H),  3.98 (s, 6H), 3.89 (s, 3H),
2.67 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=157.6$, 154.1 (2C), 150.3, 147.5, 141.9, 136.1, 131.6, 131.0,
128.7, 127.6, 125.2, 122.6, 104.4 (2C), 61.0, 56.3 (2C), 19.4;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{19}H\tsub{20}NO\tsub{3}S$^{+}$:  342.1158, found:\break 342.1161.

\subsubsection{3-(4-Fluorophenyl)-4-(methylthio){\ubreak}isoquinoline (3j)}

\vspace*{2pt}

\inlinefig{fx16}

Yellow solid (82 mg, 61\%); mp ${=}$\ 124--127~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.35$
(s, 1H), 8.24--8.17 (m, 3H), 7.88 (d, $J=6.8$ Hz, 1H),  7.80--7.75 (m,
1H), 7.62--7.57 (m, 1H), 7.28--7.22 (m, 2H), 2.78  (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=161.7$ (d, $J=244$ Hz), 156.3, 148.4, 144.9, 135.2 (d, $J=244$
Hz) 129.0, 128.3 (d, $J=8$ Hz, 2C), 128.2, 126.0, 125.0, 123.6, 118.8,
115.7 (d, $J=17$ Hz, 2C), 17.9; \tsup{\textbf{19}}\textbf{F NMR} (100
MHz, CDCl\tsub{3}): $\delta=-113.2$; \textbf{HRMS (ESI)} ($m/z$):
[M${+}$H]$^{+}$ calcd. for C\tsub{16}H\tsub{13}FNS$^{+}$: 270.0747,
found:\break 270.0744.

\subsubsection{3-(4-Chlorophenyl)-4-(methylthio){\ubreak}isoquinoline (3k)}

\vspace*{2pt}

\inlinefig{fx17}

Brown solid (98 mg, 69\%); mp ${=}$\ 123--127~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.30$
(s, 1H), 8.24 (t, $J=7.2$ Hz, 1H), 8.12 (d, $J=6.8$ Hz, 1H), 7.95 (d,
$J=6.2$ Hz, 1H), 7.89--7.83 (m, 1H), 7.71--7.66 (m, 1H), 7.62 (d,
$J=7.2$ Hz, 2H), 3.82 (s, 3H), 2.68 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}): 
$\delta=158.1$, 151.5, 147.3, 138.6, 135.9, 131.4, 130.7, 130.1 (2C),
130.0 (2C), 128.5, 127.4, 126.1, 124.8, 18.2; \textbf{HRMS (ESI)}
($m/z$): [M${+}$H]$^{+}$ calcd. for C\tsub{16}H\tsub{13}ClNS$^{+}$:
286.0452, found: 286.0457.

\subsubsection{3-(4-Bromophenyl)-4-(methylthio){\ubreak}isoquinoline (3l)}

\inlinefig{fx18}

Dark brown solid (115 mg, 70\%); mp ${=}$\ 132--134~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.29$
(s, 1H), 8.12 (d, $J=7.8$ Hz, 2H), 7.95 (d, $J=6.6$ Hz, 1H),  7.80 (d,
$J=7.2$ Hz, 1H), 7.70--7.65 (m, 1H), 7.59 (d, $J=7.8$ Hz, 2H),
7.53--7.48 (m, 1H), 2.72 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100
MHz, CDCl\tsub{3}): $\delta=156.4$, 148.3, 143.2, 136.7, 132.1 (2C),
129.0, 128.5, 128.0 (2C), 126.2, 124.1, 122.7, 122.5, 120.8, 17.9;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{16}H\tsub{13}BrNS$^{+}$: 329.9947, found: 329.9946.

\subsubsection{3-([1,1'-Biphenyl]-4-yl)-4-(methylthio){\ubreak}isoquinoline (3m)}

\inlinefig{fx19}

White solid (128 mg, 78\%); mp ${=}$\ 142--145~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.31$
(s, 1H), 8.35 (d, $J=7.2$ Hz, 2H), 8.12 (d, $J=6.8$ Hz, 1H), 7.81 (d,
$J=7.0$ Hz, 1H), 7.72 (d, $J=7.2$ Hz, 2H), 7.66--7.61 (m, 3H),
7.55--7.50 (m, 1H), 7.46--7.41 (m, 2H), 7.36--7.31 (m, 1H), 2.34 (s,
3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=155.4$, 149.4, 141.9, 141.3, 140.1, 135.5, 132.4, 129.5 (2C),
128.4 (2C), 128.3, 128.2 (2C), 128.1 (2C), 128.0, 127.8, 127.8, 127.6,
125.2, 28.4; \textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{22}H\tsub{18}NS$^{+}$: 328.1154, found: 328.1157.

\subsubsection{3-(Furan-2-yl)-4-(methylthio)isoquinoline (3n)}

\inlinefig{fx20}

Pale yellow oil (65 mg, 54\%).

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.23$
(s, 1H), 8.14 (d, $J=7.8$ Hz, 1H), 8.07 (d, $J=7.6$ Hz, 1H), 7.78 (d,
$J=6.8$ Hz, 1H), 7.75--7.70 (m, 1H), 7.60--7.55 (m, 1H), 7.54 (d,
$J=7.0$ Hz, 1H), 7.12--7.08 (m, 1H), 2.76 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}): 
$\delta=152.9$, 147.2, 143.7, 143.0, 135.0, 134.7, 126.7, 126.3, 125.6,
124.2, 124.0, 114.9, 109.5, 17.2; \textbf{HRMS (ESI)} ($m/z$):
[M${+}$H]$^{+}$ calcd. for C\tsub{14}H\tsub{12}NOS$^{+}$: 242.0634,
found: 242.0636.

\subsubsection{4-(Methylthio)-3-(thiophen-2-yl)isoquinoline (3o)}

\vspace*{3pt}

\inlinefig{fx21}

Yellow solid (62 mg, 48\%); mp ${=}$\ 101--103~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.31$
(s, 1H), 8.10 (d, $J=7.4$ Hz, 1H), 7.81 (d, $J=7.6$ Hz, 1H), 7.68--7.64
(m, 1H), 7.63 (d, $J=4.0$ Hz, 1H), 7.49--7.44 (m, 1H), 7.17 (d, $J=5.2$
Hz, 1H), 6.88--6.85 (m, 1H), 2.68 (s, 3H); \tsup{\textbf{13}}\textbf{C
NMR} (100 MHz, CDCl\tsub{3}):  $\delta=155.9$, 147.5, 146.7, 142.0,
141.1, 128.7, 128.4, 127.2, 124.8, 122.5, 120.0, 116.9, 114.9, 17.8;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{14}H\tsub{12}NS\tsub{2}$^{+}$:  258.0406, found: 258.0401.\looseness=1

\subsubsection{4-(Methylthio)-3-(pyridin-4-yl)isoquinoline (3p)}

\vspace*{3pt}

\inlinefig{fx22}

Orange yellow solid (71 mg, 56\%); mp ${=}$\ 111--114~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.33$
(s, 1H), 8.73 (d, $J=4.8$ Hz, 2H), 8.02--7.99 (m, 3H), 7.80 (d, $J=7.2$
Hz, 1H), 7.75--7.69 (m, 1H), 7.66--7.61 (m, 1H), 2.54 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}): 
$\delta=152.7$, 151.3 (2C), 145.1, 143.6, 137.1, 133.9, 129.4, 129.0,
128.5, 128.1, 124.7, 122.0 (2C), 20.9; \textbf{HRMS (ESI)} ($m/z$):
[M${+}$H]$^{+}$ calcd. for C\tsub{15}H\tsub{13}N\tsub{2}S$^{+}$: 
253.0794, found: 253.0799.

\subsubsection{3-(\textit{tert}-Butyl)-4-(methylthio)isoquinoline (3q)}

\vspace*{3pt}

\inlinefig{fx23}

Colorless oil (50 mg, 43\%).

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=8.96$
(s, 1H), 8.03 (d, $J=7.6$ Hz, 1H), 7.91 (d, $J=7.4$ Hz, 1H), 7.66--7.61
(m, 1H), 7.49--7.44 (m, 1H), 2.65 (s, 3H), 1.47 (s, 9H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=165.4$,  151.8, 146.4, 131.4, 131.0, 130.0, 127.4, 125.6,
124.1, 37.5, 28.6 (3C), 24.8; \textbf{HRMS (ESI)} ($m/z$):
[M${+}$H]$^{+}$ calcd. for C\tsub{14}H\tsub{18}NS$^{+}$: 232.1154,
found: 232.1156.\looseness=1

\subsubsection{3-Benzyl-4-(methylthio)isoquinoline (3r)}

\vspace*{.5pc}
\inlinefig{fx24}

Pale yellow solid (68 mg, 51\%); mp ${=}$\ 125--128~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=2.37$
(s, 1H), 8.16 (d, $J=8.2$ Hz, 1H), 7.91 (d, $J=7.8$ Hz, 1H), 7.79--7.74
(m, 1H), 7.51--7.46 (m, 1H), 7.31--7.25 (m, 4H), 7.22--7.17 (m, 1H),
4.27 (s, 2H), 2.58 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz,
CDCl\tsub{3}): $\delta=153.7$, 146.7, 141.7, 140.1, 128.7, 128.5, 128.4
(2C), 127.8 (2C), 126.1, 125.7, 125.0, 123.9, 122.9, 41.5, 20.6;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{17}H\tsub{16}NS$^{+}$: 266.0998, found: 266.0993.\looseness=1

\subsubsection{3-(4-Methoxyphenyl)-7-methyl-4-(methylthio)isoquinoline
(3s)}

\vspace*{.5pc}
\inlinefig{fx25}

White solid (120 mg, 81\%); mp ${=}$\ 133--136~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.22$ 
(s, 1H), 8.07 (d, $J=7.2$ Hz, 2H), 7.89 (s, 1H), 7.81 (d, $J=6.8$ Hz,
1H), 7.65 (d, $J=6.8$ Hz, 1H), 7.99 (d, $J=7.2$ Hz, 2H), 3.83 (s, 3H),
2.47 (s, 3H), 2.32 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz,
CDCl\tsub{3}): $\delta=160.2$, 158.0, 151.3, 145.3, 140.8, 135.3,
130.4, 130.2 (2C), 129.2, 127.7, 126.4, 124.7, 115.5 (2C), 55.3, 23.1,
20.3; \textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{18}H\tsub{18}NOS$^{+}$: 296.1104, found: 296.1102.

\subsubsection{3-(4-Methoxyphenyl)-6-methyl-4-(methylthio)isoquinoline
(3t)}

\vspace*{.25pc}
\inlinefig{fx26}

White solid (122 mg, 83\%); mp ${=}$\ 132--134~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.30$
(s, 1H), 8.05 (d, $J=7.0$ Hz, 2H), 7.99 (d, $J=6.6$ Hz, 1H), 7.48 (d,
$J=6.6$ Hz, 1H), 7.41(s, 1H), 6.98 (d, $J=7.0$ Hz, 2H), 3.82 (s, 3H),
2.61 (s, 3H), 2.46 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz,
CDCl\tsub{3}): $\delta=160.7$, 155.3, 149.1, 144.6, 137.7, 133.5,
132.5, 130.7, 129.8 (2C), 128.0, 126.0, 123.7, 114.2 (2C), 55.4, 22.9,
20.1; \textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{18}H\tsub{18}NOS$^{+}$: 296.1104, found: 296.1108.

\subsubsection{3-(4-Methoxyphenyl)-8-methyl-4-(methylthio)isoquinoline
(3u)}

\vspace*{2pt}

\inlinefig{fx27}

\vspace*{2pt}

Pale yellow solid (121 mg, 82\%); mp ${=}$\ 129--131~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.32$ 
(s, 1H), 8.24 (d, $J=7.8$ Hz, 2H), 7.87 (d, $J=7.4$ Hz, 1H), 7.81 (d,
$J=7.0$ Hz, 1H), 7.58--7.53 (m, 1H), 7.04 (d, $J=7.8$ Hz, 2H), 3.88 (s,
3H), 2.74 (s, 3H), 2.55 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100
MHz, CDCl\tsub{3}): $\delta=162.8$, 146.9, 146.0, 141.5, 138.2, 133.5,
131.2, 130.7 (2C), 130.0, 128.7, 127.0, 121.3, 114.2 (2C), 55.4, 21.0,
19.3; \textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{18}H\tsub{18}NOS$^{+}$: 296.1104, found: 296.1101.

\subsubsection{3-(4-Methoxyphenyl)-6,7-dimethyl-4-(methylthio)isoquinoline 
(3v)}

\vspace*{2pt}

\inlinefig{fx28}

\vspace*{2pt}

White solid (128 mg, 83\%); mp ${=}$\ 137--139~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}):  $\delta=9.26$
(s, 1H), 8.03 (d, $J=7.6$ Hz, 2H), 7.85 (s, 1H), 7.51 (s, 1H), 7.05 (d,
$J=7.6$ Hz, 2H),  3.90 (s, 3H), 2.64 (s, 3H), 2.41 (s, 6H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=159.9$, 153.8, 147.8, 142.9, 140.4, 135.9,  133.7, 130.5, 129.8
(2C), 128.3, 124.2, 122.8, 114.1 (2C),  55.4, 21.4, 21.4, 20.1;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{19}H\tsub{20}NOS$^{+}$: 310.1260, found: 310.1261.

\subsubsection{6-Fluoro-3-(4-methoxyphenyl)-4-(methylthio)isoquinoline
(3w)}

\inlinefig{fx29}

Yellow solid (114 mg, 76\%); mp ${=}$\ 129--131~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.33$ 
(s, 1H), 8.09--8.02 (m, 3H), 7.49 (dd, $J=7.2$, 3.2 Hz, 1H), 7.43--7.37
(m, 1H), 6.98 (d, $J=7.6$ Hz, 2H), 3.82(s, 3H), 2.62 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=162.8$, 162.2 (d, $J=196.3$ Hz), 158.0, 149.5, 146.2 (d, 
$J=4.4$ Hz), 134.4 (d, $J=7.3$ Hz), 134.0, 129.7 (d, $J=7.3$ Hz), 127.7
(2C), 121.9, 121.3 (d, $J=20.5$ Hz), 117.9 (2C), 107.3 (d, $J=17.1$
Hz), 55.4, 21.1; \tsup{\textbf{19}}\textbf{F NMR} (100 MHz,
CDCl\tsub{3}): $\delta=-106.7$; \textbf{HRMS (ESI)} ($m/z$):
[M${+}$H]$^{+}$ calcd. for C\tsub{17}H\tsub{15}FNOS$^{+}$: 300.0853,
found: 300.0851.

\subsubsection{6-Chloro-3-(4-methoxyphenyl)-4-(methylthio)isoquinoline 
(3x)}

\inlinefig{fx30}

Brown solid (123 mg, 78\%); mp ${=}$\ 142--144~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.38$
(s, 1H), 8.10--8.04 (m, 3H), 7.88 (s, 1H), 7.60 (d, $J=6.4$ Hz, 1H),
7.04 (d, $J=7.8$ Hz, 1H), 3.89 (s, 3H), 2.65 (s, 3H);
\tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=158.8$,  152.5, 148.6, 144.1, 133.9, 133.7, 133.5, 132.2, 130.9
(2C), 129.8, 126.7, 124.9, 114.2 (2C), 55.4, 21.1; \textbf{HRMS} (ESI)
($m/z$): [M${+}$H]$^{+}$ calcd. for C\tsub{17}H\tsub{15}ClNOS$^{+}$:
316.0557, found: 316.0551.

\subsubsection{6-Bromo-3-(4-methoxyphenyl)-4-(methylthio)isoquinoline
(3y)}

\inlinefig{fx31}

Dark brown solid (142 mg, 79\%); mp ${=}$\ 144--146~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.24$
(s, 1H), 8.14 (d, $J=6.4$ Hz, 1H), 8.05 (d, $J=8.0$ Hz, 2H), 7.61 (s,
1H), 7.52 (d, $J=6.4$ Hz, 1H), 7.06 (d, $J=8.0$ Hz, 2H), 3.91 (s, 3H),
2.66 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz, CDCl\tsub{3}):
$\delta=159.3$, 150.7, 146.7, 142.9, 136.0, 135.6, 130.9, 130.8 (2C),
127.5, 126.9, 125.2, 123.4, 114.2 (2C), 55.4, 20.8; \textbf{HRMS (ESI)}
($m/z$): [M${+}$H]$^{+}$ calcd. for C\tsub{17}H\tsub{15}BrNOS$^{+}$:
360.0052, found: 360.0048.

\subsubsection{6-Methoxy-3-(4-methoxyphenyl)-4-(methylthio)isoquinoline 
(3z)}

\inlinefig{fx32}

White solid (129 mg, 83\%); mp ${=}$\ 129--131~\textdegree C.

\mbox{}
\tsup{\textbf{1}}\textbf{H NMR} (400 MHz, CDCl\tsub{3}): $\delta=9.35$
(s, 1H), 8.03 (d, $J=7.8$ Hz, 2H), 7.78 (d, $J=7.4$ Hz, 1H), 7.41 (d,
$J=7.4$ Hz, 1H), 7.10 (d, $J=7.8$ Hz, 2H), 6.96 (s, 1H), 3.90 (s, 3H),
3.81 (s, 3H), 2.63 (s, 3H); \tsup{\textbf{13}}\textbf{C NMR} (100 MHz,
CDCl\tsub{3}): $\delta=161.7$, 161.6, 151.0, 145.6, 140.4, 133.6 (2C),
129.9, 127.7, 123.1, 119.6, 118.6, 114.3 (2C), 108.0, 55.5, 55.4, 20.1;
\textbf{HRMS (ESI)} ($m/z$): [M${+}$H]$^{+}$ calcd. for
C\tsub{18}H\tsub{18}NO\tsub{2}S$^{+}$: 312.1053, found: 312.1051.

\vspace*{-2pt}

\printCOI

\vspace*{-2pt}

\section*{Funding}

\vspace*{-2pt}

This work was supported by Fuzhou University Zhicheng College Students'
Innovation and Entrepreneurship Training Program (2025045).

\CDRGrant[FUZC]{2025045}

\vspace*{-2pt}

\section*{Supplementary materials}

\vspace*{-2pt}

Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-447-suppl.pdf}}

\vspace*{-2pt}

\section*{Use of artificial intelligence techniques}

\vspace*{-2pt}

No artificial intelligence was used in the preparation of this
manuscript.

\vspace*{-2pt}

\back{}

\printbibliography
\refinput{crchim20250892-reference.tex}

\end{document}
