Wittig reaction with N-protected 3-(triphenylphosphonio)alaninates: Synthesis of optically active (E)-(2-arylvinyl)glycine derivatives

Article abstract of DOI:10.1248/cpb.41.252

(R)-[2-Carboxy-2-[(methoxycarbonyl)amino]ethyl]triphenylphosphonium chloride (1) was converted by treatment with anion exchange resin (HCO₃^-) into the inner salt 13h, which gave a better yield (43%) than 1 in the Wittig reaction with benzaldehyde to afford the [S-(E)]-(2-phenylvinyl)glycine derivative 24. The inner salt 13i bearing an N-benzyioxycarbonyl group was prepared by hydrogenolysis of (R)-[3-benzyloxy-2-[(benzyloxycarbonyl)amino]-3-oxopropyl]triphenylpho sphonium chloride (11e) over palladium on carbon, followed by dehydrochlorination. Hydrogenolysis of 11e over Pearlman's catalyst afforded the unprotected phosphonium chloride 12 (X = Cl). N-tert-Butoxycarbonylation of 12 followed by dehydrochlorination afforded 13j, which was more efficiently prepared through hydrogenolysis of (R)-[3-benzyloxy-2-[(tert-butoxycarbonyl)amino]-3-oxopropyl]triphenylp hosphonium chloride (11f). The usefulness of 13h-j as building blocks for the synthesis of configurationally labile (2-arylvinyl)glycine derivatives was exemplihed by the Wittig reactions with piperonal, which exclusively afforded the (E)-isomers 18h-j with high optical purity in 28-39% yield.

Full text of DOI:10.1248/cpb.41.252

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