O R1 R2 SnCl2•2H2O–Mg THF–H2O Cl OH R2 R1 O O O O PhCH CH2 O PhCH CHPh O PhOCH2CH CH2 O ClCH2CH CH2 O OH Cl Cl OH Cl OH Cl OH Cl CHCH2OH Ph Cl CHCHOH OH Ph OH CHCH2Cl PhOCH2 OH CHCH2Cl ClCH2 180 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 180† Efficient Nucleophilic Cleavage of Oxiranes to Chlorohydrins† Chintamani Sarangi,a Nalin B. Das,*a Bhagabat Nanda,a Amaendu Nayaka and Ram P. Sharmab aRegional Research Laboratory, Bhubaneswar-751013, India bCentral Institute of Medicinal and Aromatic Plants, Lucknow-226015, India SnCl2 .2H2O–Mg and THF–H2O is an efficient system for the conversion of oxiranes into chlorohydrins.Epoxides are valuable intermediates in organic synthesis partly because of their nucleophilic cleavage leading to 1,2-difunctionalized systems and partly because such cleavages usually occur specifically with trans stereochemistry. The formation of halohydrins from epoxides has been extensively studied with a variety of reagents.1–8 Although there is precedent for the Lewis acid assisted cleavage of oxiranes to halohydrins, these reactions often afford only modest yields.The present work was undertaken in order to determine the general applicability of the reaction with epoxides. In continuation of our earlier studies on the uses of metal reagents,9,10 we found that SnCl2 .2H2O–Mg and THF–H2O is a promising system for the regioselective ring opening of oxiranes to the corresponding chlorohydrins in good yields.In acidic medium1 there is usually a greater tendency for nucleophilic attack at the more substituted carbon atom. Phenyl substituents at the epoxide ring can stabilize an intermediate positive charge by conjugation, and hence attack occurs at the more substituted carbon atom. However, in the case of epoxides with electron withdrawing substituents, nucleophilic attack at the unsubstituted carbon is usually favoured. Under these conditions, substituted epoxides (Table 1, entries 4, 7 and 8) reacted regioselectively affording the primary chloride.The cyclohexene oxide and the epoxide (entries 2 and 3 respectively) opened cleanly to afford the trans chlorohydrins, with the tertiary chloride being the major product in the latter case. However in the case of styrene oxide the secondary chloride predominates. The yield of the products corresponds to the total yield of the regioisomers. Cleavage of the oxirane ring has also been unsuccessfully attempted using SnCl2 .2H2O–THF alone.However, the use of a stoichiometric amount of magnesium facilitated the reaction. In addition, the possibility of active zero-valent tin (generated in situ by the reduction of SnII to Sn0 in the presence of magnesium) could effectively induce regioselective nucleophilic attack. Owing to the general interest in the smooth and selective cleavage of these compounds, mild reaction conditions, good yields and some possible synthetic applications, the SnCl2 .2H2O–Mg–THF system will be a useful addition to the existing findings.Experimental 1H NMR spectra were recorded on deuteriochloroform on a JEOL FX-90 instrument. IR spectra were recorded on a JASCO FT/IR-5300 instrument in chloroform. Mass spectra were recorded on an MS-30 instrument. TLC and preparative TLC were performed on silica gel (E. Merck). General Procedure.·In a typical procedure, a mixture of SnCl2.2H2O (442 mg, 2 mmol), Mg powder (36.5 mg, 1.5 mmol) and oxirane (1 mmol) in THF (10 ml) was stirred at room temperature.An exothermic reaction occurred with the liberation of hydrogen. The reaction mixture was stirred for 30 min. After completion of the reaction (TLC), usual work-up and purification by preparative chromatography yielded the corresponding chlorohydrins. Selected 1H NMR spectral data. For trans-2-chlorocyclohexanol: dH (CDCl3) 1.1–1.95 (8 H, m), 2.65 (1 H, br s), 3.05–3.5 (2 H, m). For 1-chloromethylcyclohexanol: dH (CDCl3) 1.2–1.75 (10 H, m), 2.15 (1 H, br s), 3.15 (2 H, s).For 1-chlorohexan-2-ol: dH (CDCl3) 1.15 (3 H, s), 1.35–1.95 (6 H, m), 2.6 (1 H, br s), 3.8 (2 H, d), 4.85 (1 H, t). For 2-chloro-2-phenylethanol: dH (CDCl3) 2.36 (1 H, s), 3.95–1.95 (2 H, d), 5.05 (1 H, t), 7.48 (5 H, m). We thank Professor H. S. Ray, Director, and Dr Y. R. Rao, Head, F&M Division, Regional Research Laboratory, for their valuable suggestions. C. S. acknowledges the pool scheme of the Government of India.Received, 18th November 1996; Accepted, 11th February 1997 Paper E/6/07796J References 1 J. G. Smith, Synthesis, 1984, 629. 2 H. O. House, Modern Synthetic Reactions, Benjamin, Menlo Park, 1972, p. 301. 3 M. A. Loreto, L. Pellacani and P. A. Tardella, Synth. Commun., 1981, 11, 287. 4 J. Kagan, B. E. Firth, N. Y. Shih and C. G. Boyajian, J. Org. Chem., 1977, 42, 343. 5 E. Mincione, G. Ortaggi and A. Sirna, J. Org. Chem., 1979, 44, 1569. 6 T. W. Bell and J. A. Ciaccio, Tetrahedron Lett., 1986, 27, 827. 7 C. L. Spawn, G. J. Drtina and D. F. Weiner, Synthesis, 1986, 315. 8 C. Einhorn and J. L. Luche, J. Chem. Soc., Chem. Commun., 1986, 1368 and references cited therein. 9 C. Sarangi, A. Nayak, B. Nanda, N. B. Das and R. P. Sharma, Tetrahedron Lett., 1995, 36, 7119. 10 C. Sarangi, A. Nayak, B. Nanda, N. B. Das and R. P. Sharma, J. Chem. Res. (S), 1996, 28 and references cited therein. *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Table 1 Oxirane ring opening with SnCl2.2H2O–Mg–THF–H2O Entry Oxirane Producta Yield (%)b 1 64 2 72 3 75 4 77 5 90 6 78 7 86 8 74 aAll the products gave satisfactory spectral data. bTotal yield of the regioisomers.