(S)-tert-Leucine [(S)-l4] is diazotized affording a mixture of the expected a-chloro and a- hydroxy acids (S)-15 and (S)-16 and the rearranged P-chloro and P-hydroxy acids (R)-12 and (S)-11. Separation produces a 51% yield of pure (S)-15 (ee 2 97.4%) which is converted via the acid chloride (S)-17 into the a-chloro amides (S)-18a and b (ee= 99.0 and 95.2%, respectively). On treatment with tBuOK, the latter is converted into the a-lactam (R)-22b ( ...
