Unsubstituted or alpha- and beta-C-substituted silylepoxides react stereospecifically with lithium diphenylphosphide, optionally followed by methylation, to give vinylphosphonium iodides or vinylphosphine oxides resulting from alpha-opening and silyl enol ethers, vinylsilanes or alpha-hydroxysilanes by beta-opening. On the other hand, alpha,beta- or alpha,alpha-disilylepoxides afforded beta-silyl vinylphosphine oxides or alpha-silylated silyl enol ethers by alpha- and beta-cleavage, respectively. All compounds are interesting synthons in organic chemistry.