Alkoxide induced rearrangement of alkyl bromomethylphosphonamidates: steric influences on the direction of ring opening of the azaphosphiridine oxide intermediate

Abstract

Methyl P-bromomethyl-N-tert-butylphosphonamidate 10 (R = Me) rearranges with methoxide, giving dimethyl tert-butylaminomethylphosphonate 12 (R = R′ = Me) and dimethyl N-tert-butyl-N-methylphosphoramidate 13 (R = R′ = Me) in comparable amounts. These products are derived from the (postulated) azaphosphiridine oxide intermediate 11 (R = Me) by nucleophilic attack at phosphorus and cleavage of the P–N or P–C bond. Increased bulk in the alkyl group of the alkoxy ligand (R = methyl < cyclohexyl < tert-butyl < menthyl) or the alkoxide nucleophile (methoxide < tert-butoxide) increases P–N bond cleavage at the expense of P–C cleavage.