3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 7. Protonation and O-alkylation of simple 1H-pyrrol-3(2H)-ones: crystal and molecular structure of 3-hydroxy-1-t-butyl-1,2-dihydropyrrolium picrate

Abstract

O-Protonation of 1H-pyrrol-3(2H)-ones gives cations which are stable indefinitely in solution, and can be isolated as picrate salts. An X-ray crystal structure of the 1-t-butyl derivative confirms charge delocalisation in these cations, which can be regarded as the Wheland intermediates for protonation of 3-hydroxypyrrols. Deuterium exchange at the 2- and 4-position under acidic conditions takes place via the hydroxypyrrole and pyrrolone tautomers, respectively, of the free base. 2,2-Disubstituted 1H-pyrrol-3(2H)-ones are found to give O-alkylated salts on treatment with Meerwein's reagent.