STEREOSELECTIVE OXIRANE FORMATION BY REACTION OF DIAZOMETHANE ON 1-FLUORO-3-[(4-METHYLPHENYL)SULFINYL]-3-PHENYLPROPAN-2-ONE

(2S,2'R,R(s))-2-(Fluoromethyl)-2-{[(4-methylphenyl)sulfinyl][phenyl]methyl} oxirane (4) was obtained in high chemical yield and with high diastereoselectivity by reacting diazomethane with pure (3R,R(s))-1-fluoro-3-[(4-methylphenyl)sulfinyl]-3-phenyl-propan-2-one (3), but also with its (3S,R(s))-3-diastereoisomer, in the latter case through inversion of the configuration at carbon 3. The corresponding methyl enol ethers 6 were isolated as by-products. NMR experiments and molecular modelling calculations were performed in order to clarify the equilibria in solution and the preferred conformations of both ketones 3. Several variously substituted, sulfur-free tertiary alpha-(fluoromethyl)carbinols ware obtained from the main reaction product (2S,2'R,R(s))-4 through appropriate elaborations of the sulfinyl group and of the oxirane ring. The structure of(2S,2'R,R,)-4 was established by X-ray analysis of the open-chain derivative (2S,2'R,R(s))-1-bromo-3-fluoro-2'-{[(4-methylphenyl)sulfinyl][phenyl]methyl}propan-2-ol (7).