Regiospecific Lithiation of Phenoxazine Ortho to the Oxygen Atom. Synthesis of 4-Mono- and 4,6-Disubstituted Phenoxazine Derivatives

Article abstract of DOI:10.1021/jo00270a027

Under appropriate conditions, phenoxazine bearing a sterically demanding, bulky N-substituent (e.g., α-methylbenzyl or tert-butyldimethylsilyl) undergoes lithiation at C-4 or at C-4 and C-6 with n-butyllithium in THF solution.The lithiated species react with a variety of electrophilic reagents and upon subsequent N-deprotection provide access to 4-mono- or 4,6-disubstituted phenoxazines.This process is of particular synthetic utility (36-54percent yields) when the N-substituent is tert-butyldimethylsilyl.