Synthesis of allylsilane-containing amino acids via the Claisen rearrangement

The Claisen rearrangement of N-BOC-glycinate esters 1a–1d led to the formation of α-allylsilane-functionalized amino acids 2–3 in good yield (up to 80%). The diastereoselectivity of the reaction varied from 2:1 to 29:1 (syn:anti) for 1a depending on reaction conditions. In the case of the Ireland–Claisen variant, the relationship between size of the alkyl groups on the enolate trap (Me2R′SiCl, R=Me, t-Bu, Ph) and diastereoselectivity was investigated, showing that chlorotrimethylsilane gave the best results. The size of the alkyl groups on the allylsilane do not exert a significant effect on the diastereoselectivity or yield (Me2RSi, R=Me, t-Bu, Ph, i-Pr).