Reversible Friedel-Crafts acylations of 3-alkyl-1-(phenylsulfonyl)pyrroles: Application to the synthesis of an ant trail pheromone
Friedel-Crafts acylations of 3-alkyl-1-(phenylsulfonyl)pyrroles appear to be kinetically favored at the adjacent C-2 position but rearrangement to the C-5 position can occur after prolonged reaction times. This reversible Friedel-Crafts methodology has been employed for the synthesis of the ant trail pheromone, methyl 4-methylpyrrole-2-carboxylate.
Xiao, Dong,Schreier, Jeffrey A.,Cook, James H.,Seybold, Paul G.,Ketcha, Daniel M.
p. 1523 - 1526
(2007/10/03)
Pyrrole chemistry. XXVIII. Substitution reactions of 1-(phenylsulfonyl)pyrrole and some derivatives
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.