On The Selective N-Methylation Of Boc-Protected Amino Acids

The selective N-methylation of BOC-protected valine 1a with MeI and NaH in THF (i.e, in the presence of it free carboxyl group) has been attributed to the protection of the carboxylate by chelation to Na+. An alternative mechanism, involving the Formation of the carbene intermediate generated from MeI and its Insertion Into the N-H bond, has been ruled out by isotopic labeling.