An Efficient One-Pot Conversion of THP- and TMS Ethers to Sulfonate Esters Using FeCl3-Montmorillonite K-10 Clay Barahman Movassagha and Salman Shokri Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315-1618, Tehran, Iran a Kermanshah Oil Refining Company, Kermanshah, Iran Reprint requests to Dr. B. Movassagh. E-mail: [email protected] Z. Naturforsch. 60b, 763 – 765 (2005); received March 29, 2005 Various tetrahydropyranyl and trimethylsilyl ethers are efficiently transformed into the correspond- ing sulfonate esters with sulfonyl chlorides in the presence of FeCl3-Montmorillonite K-10 clay. Key words: Sulfonate Esters, FeCl3-Montmorillonite K-10, Trimethylsilyl Ethers, Tetrahydropyranyl Ethers, Clay Catalyst Sulfonate esters are especially useful substrates in sions of THP and TMS ethers into the correspond- nucleophilic substitution reactions used in synthesis. ing carboxylic esters in the presence of Montmoril- Their preparation from alcohols is an effective way lonite K-10 clay [7, 8]. In continuation of our ongo- of installing a reactive leaving group, e.g. on an alkyl ing program to develop environmentally benign meth- chain. p-Toluenesulfonate- and methanesulfonate es- ods using supported reagents, this article describes ters are the most frequently used groups for preparative a new, simple, and efficient one-pot protocol for the work. The usual method for preparation of sulfonates deprotection-sulfonylation of THP and TMS ethers relies on the use of the corresponding sulfonyl chlo- with sulfonyl chlorides in refluxing acetonitrile using ride or anhydride in the presence of triethylamine [1], FeCl3 impregnated Montmorillonite K-10 as a mild pyridine [2], 1,4-diazabicyclo[2.2.2]octane (DABCO) and non-corrosive solid catalyst (Scheme 1). The focal [3] or aqueous base in a Schotten-Baumann type re- point of this report is on the transformations of O-C action. An alternative for preparing tosylates and me- and O-Si bonds into O-SO2 bonds. sylates is to convert the alcohol into its lithium salt, − . which is then allowed to react with the sulfonyl chlo- RO-THP FeCl3 Mont K10 + R’SO2Cl −−−−−−−−−−→ ROSO2R’ ride [4]. Sulfonic acids are also used for the synthe- RO-TMS CH3CN, reflux sis of sulfonate esters but expensive alkylating agents Scheme 1. such as trialkyl orthoformate, alkyl ethers, esters or 2- alkoxybenzothiazolium salts are employed instead of The catalyst used here can easily be prepared [9] alcohol [5]. To the best of our knowledge, direct con- from readily available and inexpensive FeCl3 and version of tetrahydropyranyl (THP) and trimethylsilyl Montmorillonite K-10 clay in dry acetonitrile. In or- (TMS) ethers into the corresponding sulfonate esters der to have a background knowledge of the activ- have not been reported in the literature. ity of the extensively used Montmorillonite clays, n- butylOTHP was treated with TsCl using different clays Results and Discussion (Table 1). It was found that FeCl3 supported Mont- morillonite K-10 is most effective among the clays Heterogeneous reactions that are facilitated by sup- for the deprotection-sulfonylation of THP ethers. The ported reagents on various solid surfaces have received iron content of the clay determined by the atomic ab- attention in recent years [6]. The advantage of these sorption technique was 0.15 mmol/g of solid catalyst. methods over conventional homogeneous reactions is Using n-butylOTHP, the amount of catalyst was opti- that they provide greater selectivity, enhanced reac- mized and an ether to clay ratio of 1 : 0.038 was taken. tion rates, cleaner products, and simplicity of handling. The catalyst can be recovered and reused after activa- Previously, we have developed several direct conver- tion at 280 ◦C. In this study, different aliphatic THP 0932–0776 / 05 / 0700–0763 $ 06.00 c 2005 Verlag der Zeitschrift f¨ur Naturforschung, T¨ubingen · http://znaturforsch.com 764 B. Movassagh – S. Shokri · An Efficient One-Pot Conversion of THP- and TMS Ethers Table 1. Deprotection-sulfonylation of n-butylOTHP using fonate esters prepared from methanesulfonyl chloride various clay catalysts. (entries 11 – 13, Table 2, and entries 10 – 12, Table 3) Clay catalyst Time (h) Yielda (%) need shorter reaction times and generally give higher Montmorillonite K-10 24 25 yields than those produced from arylsulfonyl chlorides. Montmorillonite KSF 24 20 Fe3+-Montmorillonite K-10 24 57 FeCl3-Montmorillonite K-10 7 81 Conclusion a Isolated yields. A simple, and efficient method has been developed Table 2. Preparation of sulfonate esters from THP ethers us- for one-step deprotection-sulfonylationof a wide range ing FeCl3-Mont. K-10. of THP and TMS ethers by using an inexpensive, non- Entry THP Sulfonyl Time Yielda Ref.b hazardous, and easily available catalyst. The present ether chloride (h) (%) protocol has the additional advantages of easy work- 1CH3CH2OTHP p-CH3C6H4SO2Cl 6 75 [10] up and high yield. 2CH3(CH2)2CH2OTHP p-CH3C6H4SO2Cl 7 81 [11] 3CH3(CH2)3CH2OTHP p-CH3C6H4SO2Cl 7 79 [10] 4CH3(CH2)6CH2OTHP p-CH3C6H4SO2Cl 7 80 [1] Experimental Section 5 PhCH2OTHP p-CH3C6H4SO2Cl 8 70 [12] 6CH2=CHCH2OTHP p-CH3C6H4SO2Cl 8 72 [10] FeCl3-Montmorillonite K-10 catalyst was prepared ac- 7 CyclohexylOTHP p-CH3C6H4SO2Cl 11 78 [10] cording to the method reported by Laszlo et al. [9]. All prod- 8 (CH3)2CHOTHP p-CH3C6H4SO2Cl 10 70 [10] ucts were characterized by comparison of their spectroscopic 9 D,L-CH (CH ) - p-CH C H SO Cl 11 68 [10] 3 2 5 3 6 4 2 data with those of known samples. IR spectra were obtained CH(CH )OTHP 3 using a Shimadzu 470 instrument. 1H NMR spectra were de- 10 CyclohexylOTHP C6H5SO2Cl 8 77 [10] 11 CyclohexylOTHP CH3SO2Cl 3 88 [10] termined by a Bruker AQS Avance 300 MHz spectrometer. 12 CH3(CH2)2CH2OTHP CH3SO2Cl 2 86 [11] 13 CH CH CH OTHP CH SO Cl 2 83 [13] 3 2 2 3 2 General procedure for the conversion of THP ethers into a Yields refer to pure isolated products characterized by IR and 1H NMR spectroscopy; b references for known compounds. their corresponding sulfonate esters To a stirred suspension of the THP ether (1.0 mmol), Table 3. Preparation of sulfonate esters from TMS ethers us- dry acetonitrile (6 ml), and FeCl3-Montmorillonite K-10 ing FeCl -Mont. K-10. 3 (250 mg, containing 0.038 mmol of FeCl3), the sulfonyl Entry TMS ether Sulfonyl chloride Time Yielda chloride (1.0 mmol) was added. The reaction mixture was (h) (%) heated at reflux for the time specified in Table 2. Progress 1CH3(CH2)2CH2OTMS p-CH3C6H4SO2Cl 5 78 of the reaction was monitored by TLC; on completion, after 2CH3(CH2)3CH2OTMS p-CH3C6H4SO2Cl 6 75 cooling, the catalyst was removed by filtration and the filtrate 3CH(CH ) CH OTMS p-CH C H SO Cl 6 80 3 2 6 2 3 6 4 2 was evaporated. The resulting crude product was purified 4 PhCH2OTMS p-CH3C6H4SO2Cl 7 72 and isolated by preparative TLC (silica gel, eluent petroleum 5CH2=CHCH2OTMS p-CH3C6H4SO2Cl 6 75 6 CyclohexylOTMS p-CH3C6H4SO2Cl 10 80 ether : ethyl acetate = 50 : 1) to afford the desired ester. 7 (CH3)2CHOTMS p-CH3C6H4SO2Cl 9 77 8CH(CH ) CH(CH )OTMS p-CH C H SO Cl 11 71 3 2 5 3 3 6 4 2 General procedure for the conversion of TMS ethers into 9 CyclohexylOTMS C6H5SO2Cl 7 82 10 CyclohexylOTMS CH3SO2Cl 3 87 their corresponding sulfonate esters 11 CH (CH ) CH OTMS CH SO Cl 3 85 3 2 2 2 3 2 To a solution of the TMS ether (1.0 mmol) in dry ace- 12 CH3CH2CH2OTMS CH3SO2Cl 3 85 a Isolated yields. tonitrile (6 ml) was added FeCl3-Montmorillonite K-10 clay (250 mg, containing 0.038 mmol of FeCl3). The mixture was ethers were treated with p-toluenesulfonyl, benzene- refluxed for the appropriate time (Table 3) and cooled. Af- sulfonyl, and methanesulfonyl chloride in the presence ter filtration, the filtrate was concentrated and the product of the catalyst in refluxing acetonitrile to obtain the purified and isolated by preparative TLC (silica gel, eluent corresponding sulfonate esters in good to high yields petroleum ether : EtOAc = 50 : 1). (Table 2). The catalyst, FeCl -Mont. K-10 clay, is also 3 Acknowledgements efficient for the preparation of sulfonate esters from TMS ethers (Table 3). It is worth noting that in both The authors thank K. N. Toosi University of Technology reactions carbon-carbon double bonds remains unaf- Research Council and Kermanshah Oil Refining Company fected (entry 6, Table 2, and entry 5, Table 3). Sul- for financial assistance. B. Movassagh – S. Shokri · An Efficient One-Pot Conversion of THP- and TMS Ethers 765 [1] Y. Yoshida, Y. Sakakura, N. Aso, S. Okada, Y. Tanabe, [6] A. McKillop, D. W. Young, Synthesis 401 and 481 Tetrahedron 55, 2183 (1999). (1979). [2] a) H. 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