Diastereoselective process for preparing n-substituted amino acids and derivatives

A process for preparing an (S,S) or (R,R) diastereoisomer of the formula:

• ##STR7## or salts, esters or amides thereof, wherein R.sup.3 and R.sup.4 independently represent hydrogen, alkyl, aryl or aryl substituted with halogen, alkyl, nitro or alkoxy, and n and m independently represent integers from one to six, comprising combining a cyanide compound of the formula:
• M.sup.1 C.tbd.N (III)
• wherein M.sup.1 is hydrogen, trimethylsilyl or a metal selected from the group consisting of sodium, potassium, lithium, cesium, iron, nickel, cadmium and zinc, with an optionally added proton source, a solvent and a Lewis acid of the formula:
• M.sup.2 X.sub.4, AlCl.sub.3 or BF.sub.3 (IV)
• wherein M.sup.2 is Sn or Ti and X represents chloro, bromo, fluoro or iodo, with an optically active .alpha.-amino acid compound of formula (I):
• ##STR8## or salts, esters or amides thereof, wherein R.sup.3 and m are as defined hereinbefore, followed by addition of an acyl or acetal compound of formula (II):
• ##STR9## wherein m, n and R.sup.4 are as defined hereinbefore, R.sup.1 is hydrogen, alkyl or phenyl and R.sup.2 and R.sup.3 independently represent alkyl.