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On lithiation, N -benzyl ureas varying N ‘-aryl substituents undergo a migration of the aryl ring to the α carbon of the N -benzyl group. With chiral, enantiomerically pure N -α-methylbenzyl ureas, the rearrangement is stereospecific and creates a new, fully substituted stereogenic center α to N. Removal of the urea function by N-nitrosation and hydrolysis allows the synthesis of chiral tertiary carbinamines in high enantiomeric purity.
Clayden et al. (Thu,) studied this question.