Direct synthesis of N-hydroxy beta-amino acid esters from carboxylic esters and nitrones

The direct synthesis of the title amino acid derivatives from carboxylic es ters and nitrones can be achieved in fair to good yields when lithium or ma gnesium ester enolates were treated with nitrones in THF at -78 degreesC or in Et2O at -20 to 0 degreesC, respectively. The products from the reaction of t-butyl acetate with 3,4-dihydroisoquinoline N-oxide or 5,5-dimethylpyr roline 1-oxide were transformed into (1,2,3,4-tetrahydroisoquinolin-1-ylide ne)acetate or (pyrrolidin-2-ylidene)acetate derivatives in the presence of triphenylphosphine, carbon tetrachloride. and triethylamine in refluxing di chloromethane.