A NEW METHOD FOR THE SYNTHESIS OF ALPHA-BROMOACYL SILANES VIA RING-OPENING OF 2-PHENYLSULFONYL-2-TRIMETHYLSILYLOXIRANES

2-Phenylsulphonyl-2-trimethylsilyoxiranes 2 are efficiently prepared by treatment of 2-phenylsulphonyloxiranes 3 with butyllithium in the presence of chlorotrimethylsilane at low temperatures. Reaction of 3-alkyl-2-phenylsulphonyl-2-trimethylsilyloxiranes 2, in which the alkyl group is primary, with magnesium bromide at room temperature gives 2-bromoacyl silanes 1 in good yield. Reaction at higher temperatures leads to competing formation of bromovinyl sulphones 7. Reaction of 3,3-dialkyloxiranes with magnesium bromide occurs much more readily, leading to 2-bromoacyl silanes 1 in moderate yields. Other products derived from a common carbocationic intermediate are also isolated.