Ring-Opening of Epoxides by Pendant Silanols

We present a new ring-opening reaction of epoxides by pendant silanols, catalyzed by either Ph3C+BF4– or BINOL-phosphoric acid. In all cases examined, the reaction is perfectly regioselective and diastereoselective. Silanol epoxides derived from trans-allylic alcohols, cis-allylic alcohols, trans-homoallylic alcohols, and cis-homoallylic alcohols were all compatible and gave products from either endo- or exo-ring opening. With silanol epoxides derived from 4-alkenyl silanols, an unusual rearrangement to tetrahydrofuran products was observed, which is likely the result of tandem nucleophilic attacks. The utility of this methodology was demonstrated in a short preparation of protected D-arabitol.