Stereocontrolled synthesis of quaternary beta,gamma-unsaturated amino acids: chain extension of D- and L-alpha-(2-tributylstannyl)vinyl amino acids

A pair of diastereomeric (4S,5S)- and (4S,SR)-4-methoxycarbonyl-5-phenylsel enomethyl-2-phenyl oxazolines, derived from L-vinylglycine, serve as precur sors to protected, quaternary, L- and D-alpha-(2-tributylstannyl)vinyl amin o acids, respectively, in three steps {(i) alkylative side chain installati on, (ii) eliminative ring-opening and (iii) vinyl selenide to vinyl stannan e interconversion}. The title compounds may be protodestannylated to the co rresponding free, quaternary L- and D-vinyl amino acids. Alternatively, the 2-stannylvinyl alpha -branch (or the derivative 2-iodovinyl branch) may be exploited to access novel quaternary, L- and D-beta,gamma -unsaturated ami no acids via a range of transition metal-mediated cross-coupling reactions. (C) 2001 Elsevier Science Ltd. All rights reserved.