Acid-catalyzed rearrangement of α-hydroxytrialkylsilanes

Cationic rearrangement of several α-hydroxysilanes is described. Treatment of both (1R,1′R,2′S)-α-hydroxycyclopropylsilane and under aqueous H2SO4 underwent rearrangement via a common α-silyl cation intermediate to give a mixture of the ring-opened (R)-vinylsilane , the tandem [1,2]-CC bond migration product , and its 1′S isomer . On the other hand, the acidic treatment of (R,E)-α-hydroxyalkenylsilane or was each accompanied with partial racemization to give an enantiomeric isomer of allylic alcohol via a preferential syn-facial SN2′ reaction, respectively. Both α-hydroxyalkynylsilane and α-hydroxyalkylsilane were inert to the acidic conditions; however, treatment of (R)-α-mesyloxyalkynylsilane under aqueous H2SO4 gave a mixture of the optically active rearranged allene , α,β-unsaturated ketone , and (S)-α-hydroxyalkynylsilane with partial racemization. Comparisons of the reactivities of these α-hydroxysilanes under acidic conditions are also disclosed.