Variation in site of lithiation with ring substituent of N′-aryl-N,N-dimethylureas: Application in synthesis

Abstract

Lithiation of various N′-aryl-AW-dimethylureas takes different courses dependingon the substituent in the aryl ring. N′-(4-Chlorophenyl)-, N′-(4-fluorophenyl)- and Ar′-(4-trifluoromethylphenyl)-Ar,Ar-dimethylureas are doubly lithiated, on nitrogen and on the carbon at position 2, with //-butyllithium or