Towards Functionalized Silicon-Containing alpha-Amino Acids:Asymmetric Syntheses of Sila Analogs of Homoserine and Homomethionine

摘要

The homoserine and homomethionine sila analogs,( R )-HOSi(Me_2)CH_2CH(NH_2)CO_2H ((R )-21) and (R)-MeSCH_2Si(Me_2)CH_2(NH_2)CO_2H ((R)-24).respectively,were each synthesized in nine steps and in 30 and 23% overall yield,respectively,from commercially available ClSiMe_2CH_2Cl.The key step of both syntheses was the asymmetric alpha-bromination of an Evans amide to introduce the stereogenic center of the amino acids with defined absolute configuration.While the preparation of the homomethionine analog (R)~24 followed the expected pathway,the sila analog of homoserine.(R)-21,was unexpectedly formed during the catalytic hydrogenation of an N_3CH_2-substituted silane derivative.