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.