\makeatletter
\@ifundefined{HCode}
{\documentclass[screen,CRCHIM,Unicode,biblatex,published]{cedram} 
\addbibresource{crchim20240834.bib}
\newenvironment{noXML}{}{}
\def\tsup#1{$^{{#1}}$}
\def\tsub#1{$_{{#1}}$}
\def\thead{\noalign{\relax}\hline}
\def\tbody{\noalign{\relax}}
\def\endthead{\noalign{\relax}\hline}
\def\tabnote#1{\vskip4pt\parbox{.95\linewidth}{#1}}
\usepackage[figuresright]{rotating}
\RequirePackage{etoolbox}
\def\jobid{crchim20240834}
\def\tpar#1{\\{\centering
  \vspace*{3pt}#1}}
\def\inlinefig#1{\includegraphics{#1}}
\newenvironment{xxcenter}{\begin{center}}{\end{center}}
\def\xsection#1{}
%\graphicspath{{/tmp/\jobid_figs/web/}}
\graphicspath{{./figures/}}
\usepackage[T1]{fontenc}
\usepackage{comment}
\newcounter{runlevel}
\usepackage{upgreek}
\let\MakeYrStrItalic\relax
\def\Smallskip{\smallskip}
\csdef{Seqnsplit}{\\}
\def\refinput#1{}
\def\back#1{}
\def\0{\phantom{0}}
\def\hyphen{\mbox{-}}
\newenvironment{inftab}{}{}
\def\xmorerows#1#2{#2}
\usepackage{multirow} 
\def\nrow#1{\@tempcnta #1\relax%
\advance\@tempcnta by 1\relax%
\xdef\lenrow{\the\@tempcnta}}
\def\morerows#1#2{\nrow{#1}\multirow{\lenrow}{*}{#2}}
\def\botline{\\\hline}
\def\Lbreak{\newline}
\def\ubreak{\break}
\def\xvarnothing{\emptyset}
\def\mn{\phantom{$-$}}
\def\og{\guillemotleft}
\def\fg{\guillemotright}
\def\bgamma{\boldsymbol{\gamma}}
\makeatletter
\g@addto@macro{\UrlBreaks}{\UrlOrds}
\gappto{\UrlBreaks}{\UrlOrds}
\makeatother
\DOI{10.5802/crchim.357}
\datereceived{2024-10-10}
\daterevised{2024-10-21}
\dateaccepted{2024-10-21}
\ItHasTeXPublished
\def\etal{et~al.}
}{\documentclass[crchim]{article}
\def\CDRsupplementaryTwotypes#1#2{}
\def\CDRdoi{10.5802/crchim.357} 
\newenvironment{sidewaystable}{\begin{table*}}{\end{table*}}
\def\href#1#2{\url{#1}}
\def\xsection#1{}
\def\tpar#1{\Tg</p>\Tg<p>#1}
\newenvironment{xxcenter}{}{}
\def\Smallskip{}
\let\newline\break
\def\ubreak{}
\let\xvarnothing\emptyset
\makeatletter
}
\makeatother

\usepackage[T1]{fontenc}
\usepackage{upgreek}

%\copyeditor{RB}

\dateposted{2025-02-19}
\begin{document}

\begin{noXML}

\CDRsetmeta{articletype}{research-article}

\title{Silver-, gold-, and platinum-catalyzed [4+2] cyclizations:
synthesis of 2,3,3\textit{a},4-tetrahydro-1\textit{H}-{\allowbreak}benzo[\textit{f}]isoindol-1-one
derivatives}

\alttitle{Cyclisations-[4+2] catalys\'{e}es par des complexes d'argent,
d'or ou de platine : synth\`{e}se de
2,3,3\textit{a},4-t\'{e}trahydro-1\textit{H}-benzo[\textit{f}]isoindol-1-ones}

\author{\firstname{Keyu} \lastname{Mao}\CDRorcid{0009-0003-3226-692X}}
\address{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de Nice,
Valrose Park, 06108,{\break} Nice Cedex 2, France}

\author{\firstname{Kristina} \lastname{Plevova}\CDRorcid{0000-0003-0047-3855}}
\addressSameAs{1}{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de Nice,
Valrose Park, 06108,{\break} Nice Cedex 2, France}

\author{\firstname{Xi} \lastname{Chen}\CDRorcid{0000-0001-7303-148X}}
\addressSameAs{1}{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de
Nice, Valrose Park, 06108,{\break} Nice Cedex 2, France}

\author{\firstname{Laura Juliana Prieto} \lastname{Pabon}}
\addressSameAs{1}{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de
Nice, Valrose Park, 06108,{\break} Nice Cedex 2, France}

\author{\firstname{Sophie} \lastname{~Poulain-Martini}\CDRorcid{0000-0001-5601-7571}\IsCorresp}
\addressSameAs{1}{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de
Nice, Valrose Park, 06108,{\break} Nice Cedex 2, France}
\email[S. Poulain-Martini]{sophie.martini@univ-cotedazur.fr}

\author{\firstname{V\'{e}ronique} \lastname{Michelet}\CDRorcid{0000-0002-2217-9115}\IsCorresp}
\addressSameAs{1}{Universit\'{e} C\^{o}te d'Azur, Institut de Chimie de
Nice, Valrose Park, 06108,{\break} Nice Cedex 2, France}
\email[V. Michelet]{veronique.michelet@univ-cotedazur.fr}

\keywords{\kwd{Catalysis}
\kwd{Silver}
\kwd{Domino reaction}
\kwd{Cyclization}}

\altkeywords{\kwd{Catalyse}
\kwd{Argent}
\kwd{R\'{e}action domino}
\kwd{Cyclisation}}

\begin{abstract}
An efficient intramolecular domino cyclization/Friedel--Crafts type
transformation of \textit{N}-(alkenyl)-amide-1,6-enynes has been
developed under silver, gold, and platinum catalysis. The optimization
of this process in the presence of silver complexes led to
functionalized tri- and tetracyclic derivatives in good to excellent
yields. The reaction conditions were found to be amenable with
electron-donating and electron-withdrawing groups (12 polycyclic
adducts). For mono- and non-substituted enynes, gold and platinum
complexes were found to be efficient.
\end{abstract}

\begin{altabstract}
Une transformation intramol\'{e}culaire efficace de type domino
cyclisation / r\'{e}action de Friedel-Crafts
d'\'{e}nynes-1,6-\textit{N}-(alc\'{e}nyl)-amide a \'{e}t\'{e}
d\'{e}velopp\'{e}e, en pr\'{e}sence de catalyseurs d'argent, d'or et de
platine. L'optimisation de ce processus en pr\'{e}sence de complexes
d'argent a conduit \`{a} des d\'{e}riv\'{e}s tri- et t\'{e}tracycliques
fonctionnalis\'{e}s avec des rendements bons \`{a} excellents. Les
conditions de r\'{e}action se sont r\'{e}v\'{e}l\'{e}es favorables avec
des groupements donneurs et accepteurs d'\'{e}lectrons (12 adduits
polycycliques). Les complexes d'or et de platine se sont
r\'{e}v\'{e}l\'{e}s efficaces pour les \'{e}nynes mono- et
non-substitu\'{e}s.
\end{altabstract}

\shortrunauthors

\thanks{Centre National de la Recherche Scientifique, Universit\'e
C\^ote d'Azur, China Scholarship Council.}

\maketitle
\vspace*{1pc}

\twocolumngrid
\end{noXML}

\section{Introduction}

\begin{scheme*}
\includegraphics{sc01}
{\vspace*{6pt}}
\caption{\label{sch1}[4$+$2]-cycloaddition reaction of
${N}$-alkenylamide-1,6-enynes.}
{\vspace*{-2pt}}
\end{scheme*}

Silver
made its first appearance around 5000 BC, recognized as a soft,
malleable, ductile, shiny white precious metal. Owing to its outer
orbital 5s$^{1}$ electronic structure, silver is able to form a
variety of silver(I) salts/complexes with diverse counterions, such as
oxides, sulfides, phosphides, olefin complexes, and others. The typical
d$^{10}$ electronic configuration enables silver to coordinate with
many ${\uppi}$-donors, including N-, O-, and S-donor groups like
alkynes, alkenes, and various unsaturated bonds containing carbon and
heteroatoms~\cite{1,2,3,4,5}. {Furthermore}, because of the vacant f
orbitals and relativistic contraction, Ag demonstrates ${\upsigma}$-~or
{${\uppi}$-Lewis} acidity with a tendency for ${\upsigma}$-coordination
over ${\uppi}$-coordination~{\cite{6,7}.} The first documented instance
of a silver-catalyzed reaction, converting ethylene into ethylene
oxide, was noted in the 1930s~\cite{8}. Historically, silver was perceived to have
lower catalytic activity and efficiency compared to other transition
metals. However, in recent decades, the exploration of silver-based
catalysts has progressed swiftly under both heterogeneous and
homogeneous conditions~\cite{11,12,13,14,15,16,17}.  Regarding
1,6-enynes, the literature contains a limited number of cases of
silver-catalyzed {cyclizations}. Porcel and Echavarren reported in 2007
the {first} silver-catalyzed intramolecular carbostannylation of
1,6-enynes utilizing [AgOTf(PPh$_{3}$)]$_{3}$ as a catalyst~\cite{17}
(Scheme~\ref{sch1}, Equation~(1)). In 2013, Shin's group {disclosed} 
{silver-catalyzed} cycloisomerization reactions of propiolamide derived
1,6-enynes in the case of ${N}$-arylamides~\cite{18}
(Scheme~\ref{sch1}, Equation~(2)). For this kind of substrate, the
carbonyl group was demonstrated to be a key group for the
silver-catalyzed 5-\textit{exo}-dig selective cyclization. The employment
of Au(IPr)NTf$_{2}$ led to lower selectivity, with 1,4-diene
accompanied by 1,3-diene. A 6-\textit{endo}-dig cyclization of
1,6-enyne systems was proposed in the presence of
a gold(I) cationic system~\cite{19,20}. Moreover, theoretical calculations
showed the importance of both the aryl group in the terminal
position of the alkyne and the carbonyl group (Scheme~\ref{sch1},
Equation~(3)). Following our endeavor towards organometallic catalysis
and more specifically silver- and gold-catalyzed
cyclization~\cite{21,22,23,24,25,26}, we became interested in using propiolamide
as the linker for enyne derivatives. We~and other authors recently described
preliminary results on {intramolecular} [4$+$2]-cycloaddition of
${N}$-(3-methylbut-2-en-1-yl)-amide-1,6-enyne in the presence of Ag
catalyst~\cite{18,25,26}. We report herein our full study including
the complementary activity of silver, gold, and platinum complexes
(Scheme~\ref{sch1}, Equation~(4)).\looseness=-1

\begin{scheme*}
\includegraphics{sc02}
{\vspace*{6pt}}
\caption{\label{sch2}A three-step synthesis of \textbf{5a--l}.}
{\vspace*{-2pt}}
\end{scheme*}

\section{Results and discussion}
The syntheses of the starting enyne derivatives \textbf{5a--5l} were
accomplished through a three-step reaction sequence (Scheme~\ref{sch2}).
The strategy to prepare ${N}$-tosylpropiolamides was realized starting
from the aryl alkynyl carboxylic acids \textbf{3a--3e}, which were
either commercially available (\textbf{3a}) or obtained by Sonogashira
cross-coupling from propiolic acids \textbf{3b--3e} and aryl iodides
(Scheme~\ref{sch2}). Different aryl alkynyl carboxylic acids were
prepared via a copper-free Sonogashira coupling from propiolic
acid and aryl halides. This method implied the use of
1,8-diazabicyclo[5.4.0]undec-7-ene/DBU (2.4 equiv) and
Pd(PPh$_{3}$)$_{4}$ (2.5~mol\%) in DMSO. As shown in Scheme~\ref{sch2},
the aryl alkynyl carboxylic acids \mbox{\textbf{3b--3e}} bearing
electron-donating groups such as \textit{ortho}-methyl,
\textit{para}-methyl, and \textit{para}-methoxy and electron-withdrawing
groups such as \textit{para}-bromo, \mbox{\textit{meta}-bromo}, and
\textit{para}-CF$_{3}$, on the phenyl ring, were efficiently obtained
in 58\% to 85\% yields. The next step was the condensation of
commercially available 4-methylbenzenesulfonyl isocyanate and various
bromo-alkenes. This one-pot process was performed on the prepared
carboxylic acids \textbf{3b--3e} by treatment with allylic bromides, and
several functionalized enynes were isolated (\textbf{5a--5l}) in modest
to good yields (29--79\%). 

We started to investigate the reaction of enyne \textbf{5a} in the
presence of a catalytic amount of silver salt (Table~\ref{tab1}).
Previous studies have shown that dichloromethane and nitromethane were
the best solvents for such transformation~\cite{25,26}. We {therefore}
made a large screening of silver salts 
(\mbox{Table~\ref{tab1}}, entries
1--16) in both solvents. The best results were obtained in the case of
AgSbF$_{6}$ and AgNTf$_{2}$ in dichloromethane (Table~\ref{tab1},
entries~1 and 3, respectively). As anticipated, AgBF$_{4}$ and AgOTf gave similar
results (Table~\ref{tab1}, entries 5 and 6; 7 and 8, respectively). Some salts like AgF and
AgClO$_{4}$ gave no conversion, most probably because of low solubility
in the solvents (Table~\ref{tab1}, entries 9 and 10; 13, respectively). We tried to
correlate the activity of silver salts with the p$K_a$ of their respective
counteranion~\cite{27}, but no trends were obtained. 
We also wanted to
compare the reactivity of \textbf{5a} in the presence of silver and
gold complexes. We therefore engaged enyne \textbf{5a} in the presence
of the cationic PPh$_{3}$AuNTf$_{2}$ {complex,} which prevented any
presence of silver salt. A~\mbox{modest} activity of gold was observed,
allowing the formation of \textbf{6a} in 50\% and 36\% yield,
respectively, in dichloromethane and nitromethane (Table~\ref{tab1},
entries 17 and 18, respectively).

\begin{table}
\caption{\label{tab1}Optimization of reaction conditions
\vspace*{4pt}\tpar{\protect\inlinefig{fx01}}\vspace*{-6pt}}
\begin{tabular}{cccc}
\thead
Entry & Catalyst & Solvent (M) & Yield$^{\mathrm{a}}$ (\%) \\
\endthead
\01 & AgSbF$_{6}$ & CH$_{2}$Cl$_{2}$ & 97 \\
\02 & AgSbF$_{6}$ & CH$_{3}$NO$_{2}$ & 54 \\
\03 & AgNTf$_{2}$ & CH$_{2}$Cl$_{2}$ & 77  \\
\04 & AgNTf$_{2}$ & CH$_{3}$NO$_{2}$ & 69 \\
\05 & AgOTf & CH$_{2}$Cl$_{2}$  & 65  \\
\06 & AgOTf & CH$_{3}$NO$_{2}$ & 28 \\
\07 & AgBF$_{4}$ & CH$_{2}$Cl$_{2}$  & 61 \\
\08 & AgBF$_{4}$ & CH$_{3}$NO$_{2}$ & 55 \\
\09 & AgF & CH$_{2}$Cl$_{2}$  & Traces  \\
10 & AgF & CH$_{3}$NO$_{2}$ & nr \\
11 & AgOOCCF$_{3}$ & CH$_{2}$Cl$_{2}$  & 34 \\
12 & AgOOCCF$_{3}$ & CH$_{3}$NO$_{2}$ & 9 \\
13 & AgClO$_{4}$ & CH$_{2}$Cl$_{2}$ & nr \\
14 & AgClO$_{4}$ & CH$_{3}$NO$_{2}$ & 48 \\
15 & AgPF$_{6}$ & CH$_{2}$Cl$_{2}$ & 6 \\
16 & AgPF$_{6}$ & CH$_{3}$NO$_{2}$ & 49 \\
17 & PPh$_{3}$AuNTf$_{2}$ & CH$_{2}$Cl$_{2}$ & 50 \\
18 & PPh$_{3}$AuNTf$_{2}$ & CH$_{3}$NO$_{2}$ & 36
\botline
\end{tabular}
\tabnote{$^{\mathrm{a}}$\ $^1$H NMR yields with 3,4,5 trichloropyridine
as internal standard.}
\vspace*{-6pt}
\end{table}

With the optimized conditions in hand (Table~\ref{tab1}, entry 1), the
scope and limitations of this domino transformation were evaluated
(Scheme~\ref{sch3}). The dimethyl derivative \textbf{6a} was isolated in
89\% yield. It was obvious to note that the cyclohexenyl side chain was
compatible with the whole process and led to the tetracyclic
derivatives \textbf{6e--k} in moderate to good yields. The presence of a
bromide was well tolerated, as the cyclic adduct \textbf{6c} was
isolated in an excellent 94\% yield. The success of the cyclization
appeared to be moderately dependent on the electron-donating or
electron-withdrawing character of the substituent R$^{1}$ on the aryl
group. The presence of an electron-withdrawing group in the 
\textit{para} position of the alkyne led to a lower isolated yield in the case
of the cyclohexyl substituent. Compounds \textbf{6h} and \textbf{6k}
were obtained in 38\% and 34\% yields, respectively. The presence of an
electron-donating group or an electron-withdrawing group in the \textit{meta}
position allowed the formation of the desired derivatives in 50\% (for
\textbf{6j}) and 76\% (for \textbf{6i}) yields.


\begin{scheme*}
{\vspace*{-2pt}}
\includegraphics{sc03}
{\vspace*{4pt}}
\caption{\label{sch3}Scope and limitations for the synthesis of
\textbf{6a--l}.}
\end{scheme*}

Interestingly, the disubstitution of the alkene moiety was crucial to
the cyclization. Traces of \textbf{6b} and \textbf{6d} were detected
whereas no reaction was observed in the case of \textbf{6l}. We
therefore turned our attention to substrates \textbf{5b}, \textbf{5d}, and \textbf{5l} to
further revisit their potential reactivity (Table~\ref{tab2},
Scheme~\ref{sch4}).

\begin{table}
\caption{\label{tab2}Optimization of reaction conditions for
\textbf{5b}
\vspace*{4pt}\tpar{\protect\inlinefig{fx02}}\vspace*{-6pt}}
\tabcolsep=3pt
\begin{tabular}{ccccc}
\thead
Entry & Catalyst  & Solvent (M) & $T$ (\textdegree C) & Yield$^{\mathrm{a}}$ (\%) \\
\endthead
\01 & PPh$_{3}$AuNTf$_{2}$  & CH$_{2}$Cl$_{2}$ & rt & 26 \\
\02 & IPrAuNTf$_{2}$ & CH$_{2}$Cl$_{2}$ & rt & 10 \\
\03 & PtCl$_{2}$ & CH$_{2}$Cl$_{2}$ & rt  & - \\
\04 & PPh$_{3}$AuNTf$_{2}$ & CH$_{3}$NO$_{2}$ & rt & 9 \\
\05 & PPh$_{3}$AuNTf$_{2}$ & DCE  & rt & 21 \\
\06 & PPh$_{3}$AuNTf$_{2}$ & Toluene & rt  & 33 \\
\07 & PPh$_{3}$AuNTf$_{2}$ & DCE  & 80 & 81 (66)$^{\mathrm{b}}$ \\
\08 & PPh$_{3}$AuNTf$_{2}$ & Toluene & 80 & 77 \\
\09 & IPrAuNTf$_{2}$ & DCE & 80 & 75 \\
10 & PtCl$_{2}$ & DCE & 80 & 63$^{\mathrm{b}}$ \\
11 & PtCl$_{2}$ & Toluene & 100 & 67 
\botline
\end{tabular}
\tabnote{$^{\mathrm{a}}$\ $^1$H NMR yields with 3,4,5 trichloropyridine
as internal standard; $^{\mathrm{b}}$ isolated yield.}
\end{table}

\begin{scheme*}
{\vspace*{-3pt}}
\includegraphics{sc04}
{\vspace*{4pt}}
\caption{\label{sch4}Reactivity of \textbf{5d} and \textbf{5l}.}
{\vspace*{-3pt}}
\end{scheme*}

In order to obtain \textbf{6b}, we initiated this study by
investigating the reaction in the presence of gold or platinum complex
in dichloromethane at room temperature (Table~\ref{tab2}, entries
1--3). Low to no conversions were observed. Switching
to other solvents such as nitromethane, dichloroethane, or toluene did
not give better results (Table~\ref{tab2}, entries 4--6).



Increasing 
the temperature was the key parameter, and in DCE as well as
in toluene, the desired product \textbf{6b} was isolated in 66\% and
63\% yields \mbox{(Table~\ref{tab2},} entries 7--11) with
PPh$_{3}$AuNTf$_{2}$ and PtCl$_{2}$ complexes, respectively. We therefore found three
sets of optimized conditions (Table~\ref{tab2}, entries 7, 9, and 11)
for which the yield of \textbf{6b} did not change significantly.

Under these conditions, the cyclization of \textbf{5d} and \textbf{5l}
was attempted (Scheme~\ref{sch4}). The bromo derivative \textbf{6d} was
isolated in similar yields of 63\% and 61\% by using gold and platinum,
respectively. The case of \textbf{5l} was still tricky, as
non-substituted adduct \textbf{6l} was obtained only in the case of
PtCl$_{2}$, with a very modest yield of 26\%. The yield was slightly
increased to 35\% in the presence of PPh$_{3}$AuNTf$_{2}$, which is a
preliminary promising result.

\begin{scheme}
{\vspace*{4pt}}
\includegraphics{sc05}
{\vspace*{10pt}}
\caption{\label{sch5}Mechanistic proposal.}
{\vspace*{-4pt}}
\end{scheme}

These results appeared to indicate that the reactivity of the
propiolamide derived 1,6-enynes \mbox{derivatives} could be realized by a
choice of the metal depending on the substrate (Scheme~\ref{sch5}).
Based on our studies and literature
precedents~\cite{17,18,19,20,25,26}, the first step of the mechanism
would be a ${\uppi}$-activation of alkyne \textbf{5} by coordination of
the metallic complex to the triple bond and potentially the carbonyl in
the case of silver salts. Subsequent 5-\textit{exo}-dig addition of the
alkenyl moiety would lead to intermediate \textbf{B}. This intermediate
would be stabilized in the case of R$^{2}$ and R$^{3}$ different from
an hydrogen. The Lewis acid properties of the metallic catalyst
therefore play a crucial role. In the case of disubstituted alkenes,
the silver metal may induce further \mbox{cyclization}. In the case of the
mono-substituted alkenyl side chain, or the non-substituted chain, the
transformation needs a higher electrophilic metal and therefore gold or
platinum complexes are efficient. The third elemental step would be the
addition of the aromatic ring, according to a Friedel--Crafts type
addition, which would therefore be favored in the case of
electron-donating groups. At this point, the presence of a substituent
on the alkenyl side chain may also stabilize the cationic aryl moiety.
Intermediate \textbf{C} would be then transformed to the cyclic adduct
\textbf{6}, and the catalyst regenerated by a protodeauration step.

\section{Conclusion}
In summary, we have extended the method of an intramolecular domino
metal-catalyzed sequence of ${N}$-(alkenyl)-amide-1,6-enynes leading to
2,3,3\textit{a},4-tetrahydro-1\textit{H}-benzo[\textit{f}]isoindol-1-one 
derivatives. The optimization of this process in the presence of silver
complexes revealed the importance of Lewis acid properties in view
of the alkenyl side chain. For mono- and non-substituted enynes, gold
and platinum complexes were found to be efficient. The
5-\textit{exo}-dig addition followed by a Friedel--Crafts arylation led
to tri- and tetracyclic derivatives in good to excellent yields. These
results give quite a positive prospect for the improvement of catalytic
domino processes. Further studies will be dedicated to the optimization
of an asymmetric version and the access to biologically active building
blocks.

\section*{Declaration of interests}
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 organizations.

\section*{Acknowledgments}
This work was supported by the Centre National de la Recherche
Scientifique and the Universit\'{e} C\^{o}te d'Azur. We gratefully
acknowledge UniCA for a Master grant to LJPP and China Scholarship
Council for PhD grants to KM and XC. We are grateful to the MS3U-FR2769
platform (Sorbonne Universit\'{e}) for HRMS analyses.

\back{}

\section*{Supplementary data}
Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-357-suppl.pdf}}

\printbibliography
\refinput{crchim20240834-reference.tex}

\end{document}
