Synthesis of highly enantio-enriched alpha-amino acids by carboxylation ofN-(alpha-lithioalkyl)oxazolidinones

N-(alpha-Stannylalkyl)oxazolidinones can be obtained as a mixture of diaste reomers in three steps from aldehydes with yields dependent on the R group of R-CHO. They can be transformed by a tin-lithium exchange to N-(alpha-lit hioalkyl)ox-azolidinones which equilibrate rapidly to one diastereomer. The se compounds give rise, after carboxylation, to the diastereopure N-(alpha- carboxyalkyl)oxazolidinones. Transformation of the oxazolidinone moiety to a free amino group is accomplished by a Birch-type reduction. Using this me thod, L-methionine, L-alanine, L-leucine and L-homocysteine were obtained i n good yields and ee = 92% to 95%. The short time required for the whole se quence makes this method ideal for synthesising 1-[C-11]amino acids.