Pyrrole chemistry. XXVIII. Substitution reactions of 1-(phenylsulfonyl)pyrrole and some derivatives

Abstract

The preparative value of the 1-(phenylsulfonyl) N-blocking and directing group for the synthesis of 3-acylpyrroles has been further evaluated. Acetylation and benzoylation are strongly regiospecific and give good yields. However, the regiospecificity is not general and other substitution reactions give mixtures of 2- and 3-substitution or even mostly 2-substitution. Friedel and Crafts tert-butylation gives 3-tert-butyl-1-(phenylsulfonyl)pyrrole and provides a useful route to tert-butylpyrrole, but ethylation and isopropylation give mixtures. Acylations of 2- and 3-alkyl-1-(phenylsulfonyl)pyrroles show little evidence of useful regiospecificity.