Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent vanadium(IV) porphyrin

S. Abdolmanaf Taghavi; Majid Moghadam; Iraj Mohammadpoor-Baltork; Shahram Tangestaninejad; Valiollah Mirkhani; Ahmad Reza Khosropour

doi:10.1016/j.crci.2011.09.009

Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent vanadium(IV) porphyrin

S. Abdolmanaf Taghavi ¹ ; Majid Moghadam ¹ ; Iraj Mohammadpoor-Baltork ¹ ; Shahram Tangestaninejad ¹ ; Valiollah Mirkhani ¹ ; Ahmad Reza Khosropour ¹

¹ Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran

Comptes Rendus. Chimie, Volume 14 (2011) no. 12, pp. 1095-1102.

Résumé

In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) is reported. This new electron-deficient V(IV) compound was used as a highly efficient catalyst for pyranylation of primary (aliphatic and benzylic), sterically-hindered secondary and tertiary alcohols with DHP. Tetrahydropyranylation of phenols with DHP was also performed to afford the desired THP-ethers. The chemoselectivity of this method was also investigated. The results indicated that primary alcohols are more reactive in the presence of secondary and tertiary alcohols and phenols. This catalyst was reused several times without loss of its activity.

Métadonnées

Reçu le : 2011-04-23
Accepté le : 2011-09-19
Publié le : 2011-11-04

DOI : 10.1016/j.crci.2011.09.009

Mots clés : Vanadium porphyrin, Electron-deficient, Alcohols, Phenols, THP ether

Affiliations des auteurs :

S. Abdolmanaf Taghavi ¹ ; Majid Moghadam ¹ ; Iraj Mohammadpoor-Baltork ¹ ; Shahram Tangestaninejad ¹ ; Valiollah Mirkhani ¹ ; Ahmad Reza Khosropour ¹

¹ Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran

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     author = {S. Abdolmanaf Taghavi and Majid Moghadam and Iraj Mohammadpoor-Baltork and Shahram Tangestaninejad and Valiollah Mirkhani and Ahmad Reza Khosropour},
     title = {Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent {vanadium(IV)} porphyrin},
     journal = {Comptes Rendus. Chimie},
     pages = {1095--1102},
     publisher = {Elsevier},
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     doi = {10.1016/j.crci.2011.09.009},
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%A Iraj Mohammadpoor-Baltork
%A Shahram Tangestaninejad
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%A Ahmad Reza Khosropour
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S. Abdolmanaf Taghavi; Majid Moghadam; Iraj Mohammadpoor-Baltork; Shahram Tangestaninejad; Valiollah Mirkhani; Ahmad Reza Khosropour. Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent vanadium(IV) porphyrin. Comptes Rendus. Chimie, Volume 14 (2011) no. 12, pp. 1095-1102. doi : 10.1016/j.crci.2011.09.009. https://comptes-rendus.academie-sciences.fr/chimie/articles/10.1016/j.crci.2011.09.009/

Version originale du texte intégral

1 Introduction

Despite several reports on the application of metalloporphyrins in the oxidation of organic compounds [1–8], there are few reports on their applications as Lewis acid catalysts. High-valent metalloporphyrins, in which the metal is in its highest oxidation state, can be used as mild Lewis acids. In this respect, electron-deficient porphyrins of Cr(III), Fe(III), Sn(IV) and V(IV) have been used in organic transformations [9–26].

Proctection of hydroxy compounds is of great importance in organic synthesism especially in the multi step transformations [27–29]. Tetrahydropyranylation with DHP, methoxymethylation with FDMA (formaldehyde dimethyl acetal), trimethylsilylation with HMDS (hexamethyldisilazane) and acetylation with Ac₂O are the most frequently used methods for protection of hydroxy compounds [30,31]. Due to the remarkable stability of tetrahydropyranyl ethers under a variety of conditions such as alkaline media, Grignard reagents, alkyl lithiums, metal hydrides, oxidative reagents, and alkylating and acylating reagents, tetrahydropyranylation has attracted much attention in comparison with the others [30]. A variety of catalysts including protonic and Lewis acid catalysts such as p-toluene sulfonic acid (PTSA) [32], bis[trimethylsilyl]sulfate [33], (CH₃)₃SiI [34], CuCl₂ [35], DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) [36], Ru(CH₃)₃(triphosphine)](OTf)₂ [37], I₂ [38], AlCl₃.6H₂O [39], In(OTf)₃ [40], ZrCl₄ [41], K₅CoW₁₂O₄₀.3H₂O [42], ionic liquids [43], Bu₄N⁺Br₃⁻ [44], and LiOTf [45], K-10 clay [46], alumina impregnated with ZnCl₂ [47], silica chloride [48], AlCl₃@polystyrene [49], silica-based sulfonic acid [50,51], H₆P₂W₁₈O₆₂ [52], PdCl₂(CH₃CN)₂ [53], vanadyl(IV) acetate [54], BF₃-etherate [55] and homogeneous and heterogeneous [Sn^IV(TPP)(OTf)₂] [56,57] have been developed for tetrahydropyranylation of alcohols and phenols.

Vanadium is required for normal health, and could act in vivo either as a metal cation or as a phosphate analogue, depending on the oxidation state, V(lV) or V(V), respectively. In proteins, vanadium is a cofactor in an algal bromoperoxidase and in certain prokaryotic nitrogenases. However, its oxidation state within organisms seems to be highly variable. The biochemistry of vanadium potentially involves four oxidation states that are relatively stable in aqueous solution. These are V²⁺, V³⁺, VO²⁺ and VO₂⁺ (the oxidation states 2, 3, 4, and 5, respectively) [58].

In the present work, highly efficient tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran catalyzed by reusable electron-deficient tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], is reported (Scheme 1).

Scheme 1
Tetrahydropyranylation of alcohols and phenols with DHP catalyzed by [V^IV(TPP)(OTf)₂].

2 Experimental

Chemicals were purchased from Fluka and Merck chemical companies. ¹HNMR spectra were recorded in CDCl₃ solvent on a Bruker-Avance 400 MHz spectrometer. Infrared spectra were run on a Philips PU9716 or Shimadzu IR-435 spectrophotometer. Elemental analysis was carried out with a LECO, CHNS-932 instrument. UV-Vis spectra were recoreded on a Shimadzu-160 spectrophotometer. All analyses were performed on a Shimadzu GC-16A instrument with a flame ionization detector using silicon DC-200 or Carbowax 20 M columns. Tetraphenylporphyrin, [VO(TPP)] and [V(TPP)Cl₂] were prepared according to the literature [59–61].

2.1 Preparation of tetraphenyporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂]

To a solution of V(TPP)Cl₂ (0.97 g, 1 mmol) in THF (50 mL), at 55 °C, AgCF₃SO₃ (0.54 g, 2 mmol) was added. The solution was stirred at 55 °C for 30 min. The AgCl precipitate was filtered through a 0.45 μM filter. The resulting solution was evaporated at room temperature. Then, the [V^IV(TPP)(OTf)₂] was extracted with CH₂Cl₂ and the crystals were obtained after evaporation of solvent at room temperature.

Visible spectrum: 456 (Soret), 585, 628 nm; ν(KBr): 1030, 1168, 1224, 1298 cm⁻¹ (belong to SO₃ groups and porphyrin ring); CHNS analyses: Calcd. C, 57.44; H, 2.93; N, 5.83; S, 6.67 found: C, 57.35; H, 2.88; N, 5.91, S, 6.65.

2.2 General procedure for tetrahydropyranylation of alcohol and phenols with DHP catalyzed by [V^IV(TPP)(OTf)₂]

A solution of alcohol or phenol (1 mmol) and DHP (2 mmol per OH group) in THF (0.5 mL) was prepared. The [V^IV(TPP)(OTf)₂] (1 mol%) was added to this solution and stirred at room temperature. The progress of the reaction was monitored by GC. After completion of the reaction, the solvent was evaporated, Et₂O (10 mL) was added and the catalyst was filtered. The filtrates were washed with brine, dried over Na₂SO₄ and concentrated under reduced pressure to afford the crude product.

2.3 Catalyst recovery and reuse

The reusability of the catalyst was checked in the sequential pyranylation of benzyl alcohol. At the end of each reaction, the solvent was evaporated, Et₂O (10 mL) was added and the catalyst was filtered. The catalyst was used with fresh benzyl alcohol, DHP and THF.

3 Results and discussion

3.1 Investigation of catalytic activity of high-valent [V^IV(TPP)(OTf)₂] in the tetrahydropyranylation of alcohol and phenols with DHP

The preparation route for [V^IV(TPP)(OTf)₂] is shown in Scheme 2. The [V^IVO(TPP)], which can be obtained commercially or prepared in laboratory, was converted to [V^IV(TPP)Cl₂] with SOCl₂, which in turn was converted to [V^IV(TPP)(OTf)₂] with AgOTf. The catalytic activity of these three catalysts was checked in the tetrahydropyranylation of benzyl alcohol with DHP. The results showed that the catalytic activity has the following order: [V^IV(TPP)(OTf)₂](100%) > [V^IV(TPP)Cl₂] (52%) > [V^IVO(TPP)] (17%). These data showed that introducing of OTf⁻groups has a crucial effect on the catalytic activity of [V^IV(TPP)(OTf)₂]. This may be due to the electron withdrawing nature of these non-coordinated ligands which in turn increases the electron-deficiency of metal center and therefore, the catalytic activity increases. Despite of high oxophilicity of V^IV species, [V^IV(TPP)(OTf)₂] is a stable catalyst and can be used under air. Therefore, [V^IV(TPP)(OTf)₂] was chosen as catalyst for tetrahydropyranylation of alcohols and phenols. In this manner, the reaction parameters were optimized in the reaction of benzyl alcohol with DHP. As can be seen in Table 1, the best conditions are alcohol (1 mmol), DHP (2 mmol), catalyst (1 mol%) and THF as solvent. Under the optimized conditions a wide range of alcohols including primary, secondary and tertiary alcohols were converted to their corresponding THP-ethers in good to excellent yields and short reaction times. The results, which are summarized in Table 2, showed that all primary, secondary and tertiary alcohols including aromatic, aliphatic and cyclic ones were converted efficiently to their corresponding tetrahydropyranyl ethers in 3 to 8 min. In the case of aromatic alcohols, the nature of substituents has no significant effect on the product yield.

Scheme 2
The preparation route for the catalyst.

Entry	Catalyst (mol%)	DHP (mmol)	Solvent	Time (min)	Yield (%)^a
1	0.5	2	THF	3	74
2	1	2	THF	3	100
3	2	2	THF	3	100
4	1	1	THF	3	46
5	1	2	CH₃CN	3	69
6	1	2	CH₂Cl₂	3	58
7	1	2	CHCl₃	3	35
8	1	2	n-Hexane	3	19

^a GC yield.

Entry	Hydroxy compound	THP ether	Time (min)	Yield (%)^b
1			3	100
2			2	95
3			2	94
4			3	95
5			2	93
6			5	97
7			4	97
8			4	94
9			8	100
10			8	94
11			8	85
12			4	94
13			4	92
14			5	100
15			8	91
16			6	85
17			8	85
18			5	96
19			5	95

^a Reaction conditions: alcohol (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).

^b GC yield.

The ability of this catalyst in the tetrahydropyranylation of phenols was also investigated. The results showed that this catalyst efficiently converted different phenols to their corresponding THP-ethers in 3 to 5 min (Table 3).

Entry	Phenol	THP ether	Time (min)	Yield (%)^b
1			4	90
2			4	92
3			4	85
4			5	90
5			5	90

^a Reaction conditions: phenol (1 mmol), DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).

^b GC yield.

Since the catalyst was active in the tetrahydropyranylation of primary, secondary and tertiary alcohols as well as phenols, a set of competitive reactions was performed to investigate the chemoselectivity of this method. In this manner, an equimolar mixture of benzyl alcohol (primary alcohol) with benzhydrol (secondary alcohol) and 2-methyl-3-phenyl-2-propanol (tertiary alcohol), and phenol was subjected to tetrahydropyranylation with DHP (2 mmol) in the presence of [V^IV(TPP)(OTf)₂]. The results indicated that primary alcohol was more reactive in the presence of secondary and tertiary ones, and phenol (Table 4). When the same reactions were carried out in the presence of 4 mmole of DHP, the same results were obtained.

Row	ROH	THP ether	Time (min)	Yield (%)^b,c
1			3	90 (100)
				30 (37)

2			3	90 (100)
				24 (34)

3			3	92 (100)
				47 (51)

4			3	90 (100)
				14 (25)

^a Reaction conditions for a binary mixture: 1 mmole of each alcohol or phenol, DHP (2 mmol), catalyst (1 mol%), THF (0.5 mL).

^b GC yield.

^c Yields in the parentheses refer to the yields in the presence of 4 mmole of DHP.

The results obtained by this catalytic system were compared with some of those reported in the literature (Table 5). As can be seen, this catalytic system is more efficient than the others. In order to show the advantage of this method, the tetrahydropyranylation of benzyl alcohol was carried out in the presence of some of available catalysts listed in Table 5 under the same conditions described for [V^IV(TPP)(OTf)₂]. It was observed that the [V^IV(TPP)(OTf)₂]/DHP catalytic system is much more efficient than the others.


Entry	Catalyst	Catalyst (mol%)	Temperature	Time (min)	Yield (%)	Ref.
1	[V^IV(TPP)(Otf)₂]	1	R.T.	3	100	–
2	bis[trimethylsilyl]sulfate	2	0	12	97	[22]
3	CuCl₂	15	R.T.	20	83	[24]
4	AlCl₃.6H₂O	1	R.T.	30	94	[28]
5	In(Otf)₃	0.5	0	30	85	[29]
6	ZrCl₄	5	Reflux	180	92	[30]
7	K₅CoW₁₂O₄₀·3H₂O	1	R.T.	5	97	[31]
8	Ionic liquid/PPh₃.HBr	10	R.T.	240	96	[32]
9	n-Bu₄N⁺Br₃⁻ (TBATB)	2.5	R.T.	60	85	[33]
10	LiOTf	60	Reflux	150	96	[34]
11	K-10 clay	25 mg	R.T.	5	92	[35]
12	Al₂O₃/ZnCl₂	–	5	10	89	[36]
13	Silica chloride	10 mg	R.T.	10	93	[37]
14	AlCl₃@PS	15	R.T.	40	97	[38]
15	SiO₂-SO₃H	2	R.T.	15	92	[39]
16	H₆P₂W₁₈O₆₂	1	20	120	98	[41]
17	PdCl₂(CH₃CN)₂	10	R.T.	60	72	[42]
18	Vanadyl (IV) acetate	27	R.T.	60	95	[43]
19	[Sn^IV(TPP)(Otf)₂]	1	R.T.	4	96	[44]
20	[Sn^IV(TPP)(Otf)₂]@CMP	1	R.T.	4	97	[45]
21	CuCl₂	1	R.T.	3	26	–
22	AlCl₃.6H₂O	1	R.T.	3	17	–
24	ZrCl₄	1	R.T.	3	11	–
25	K₅CoW₁₂O₄₀·3H₂O	1	R.T.	3	78	–
26	LiOTf	1	R.T.	3	8	–
27	H₆P₂W₁₈O₆₂	1	R.T.	3	12	–
28	Vanadyl (IV) acetate	1	R.T.	3	10	–

The actual mechanism is not clear at present. However, based on a plausible mechanism, DHP is first activated by V(IV) porphyrin to afford 1. Nucleophilic attack of alcohol to 1 gives 2, which upon a proton transfer step produces the final product 3 and releases the catalyst for the next run (Scheme 3). Comparison of catalytic activity of [V^IV(TPP)(OTf)₂] with Vanadyl(IV) acetate shows that the presence of OTf⁻groups increases the interaction of DHP with catalyst. This can be attributed to the high electron-deficiency of V(IV) center in the presence of OTf⁻groups.

Scheme 3
The proposed mechanism for tetrahydropyranylation of alcohols and phenols with DHP catalyzed by [V^IV(TPP)(OTf)₂].

3.2 Catalyst reusability

The reusability of this catalyst was also investigated in the multiple pyranylation of benzyl alcohol with DHP under the same reaction conditions described in the general procedure. At the end of each reaction, the solvent was evaporated, Et₂O was added and the catalyst was filtered. The recovered catalyst was used with fresh benzyl alcohol and DHP. The results showed that after using the catalyst for several consecutive times (five times were checked), no decrease was observed in its catalytic activity. The nature of the recovered catalyst was monitored by its UV-Vis spectrum (Fig. 1B), in which no change was observed in its spectrum and since the catalyst retained its activity in the protection reaction, it seems that the recovered catalyst is porphyrin triflates.

Fig. 1
UV-vis spectrum of: A: [V^IV(TPP)(OTf)₂] in tetrahydrofuran (1.0 × 10⁻⁴ M, path length = 1.0 cm) at 25 °C and B: recovered [V^IV(TPP)(OTf)₂].

4 Conclusion

In conclusion, electron-deficient [V^IV(TPP)(OTf)₂] can be used as an efficient and reusable catalyst for tetrahydropyranylation of alcohols and phenols with DHP. This catalyst efficiently catalyzed the conversion of primary, secondary and tertiary alcohols as well as phenols to their corresponding THP-ethers. Short reaction times, good to excellent yields and reusability of the catalyst are noteworthy advantages of this catalytic system.

Acknowledgement

We are thankful to the Center of Excellence of Chemistry of University of Isfahan (CECUI)) for financial support of this work.

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Commentaires - Politique

1 Introduction

2 Experimental

2.1 Preparation of tetraphenyporphyrinatovanadium(IV) trifluoromethanesulfonate, [VIV(TPP)(OTf)2]

2.2 General procedure for tetrahydropyranylation of alcohol and phenols with DHP catalyzed by [VIV(TPP)(OTf)2]

2.3 Catalyst recovery and reuse

3 Results and discussion

3.1 Investigation of catalytic activity of high-valent [VIV(TPP)(OTf)2] in the tetrahydropyranylation of alcohol and phenols with DHP

3.2 Catalyst reusability

4 Conclusion

Acknowledgement

2.1 Preparation of tetraphenyporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂]

2.2 General procedure for tetrahydropyranylation of alcohol and phenols with DHP catalyzed by [V^IV(TPP)(OTf)₂]

3.1 Investigation of catalytic activity of high-valent [V^IV(TPP)(OTf)₂] in the tetrahydropyranylation of alcohol and phenols with DHP