Stereocontrolled synthesis of quaternary β,γ-unsaturated amino acids: Chain extension of D- and L-α-(2-tributylstannyl)vinyl amino acids

A pair of diastereomeric (4S,5S)- and (4S,5R)-4-methoxycarbonyl-5-phenylselenomethyl-2-phenyl oxazolines, derived from L-vinylglycine, serve as precursors to protected, quaternary, L- and D-α-(2-tributylstannyl)vinyl amino acids, respectively, in three steps ((i) alkylative side chain installation, (ii) eliminative ring-opening and (iii) vinyl selenide to vinyl stannane interconversion). The title compounds may be protodestannylated to the corresponding free, quaternary L- and D-vinyl amino acids. Alternatively, the 2-stannylvinyl α-branch (or the derivative 2-iodovinyl branch) may be exploited to access novel quaternary, L- and D-β,γ-unsaturated amino acids via a range of transition metal-mediated cross-coupling reactions.