Highly enantioselective syntheses of α-hydroxyacids using N-benzyl-4,4,7α-trimethyl--octahydro-1, 3-benzoxazine as a chiral adjuvant

Addition of Grignard and organolithium reagents to as well as hydride reduction of 2α-benzoyl-N-benzyl-4,4,7α-trimethyl- trans -octahydro-1 ,3-benzoxazine (2, Y = C6H5CO) and addition of phenylmagnesium bromide to the corresponding 2-acetyl analog (11) proceed in highly diastereoselective fashion to produce virtually exclusively the diastereomer predicted on the basis of Cram's chelate rule if chelation involves the ring oxygen atom. Mild acid hydrolysis of the adducts followed by selective oxidation produces highly enantiomerically pure ρa-hydroxyacids with clean recovery of the chiral adjuvant.