A Novel Facile Synthesis of 2,5-Di- and 2,3,5-Trisubstituted Pyrroles

Abstract

Heterocyclization of ketoximes with propyne or allene in superbase systems MOR/DMSO (M = K, Cs; R = H, t-Bu), which leads to 2-alkyl(aryl, hetaryl)-5-methyl- and 2,3-dialkyl-5-methylpyrroles or 2-methyl-4,5,6,7-tetrahydroindole in yields of up to 63%, has been accomplished for the first time. The reaction is mostly regioselective affording mainly or exclusively 2,5-di- and 2,3,5-trisubstituted pyrroles. The minor isomers in most cases are the corresponding 2,4-di and 2,3,4-trisubstituted pyrroles, only in the case of acetoxime the isomer ratio is ca 1 : 1. For oximes of methyl isopropyl ketone and pinacolone, the 4-methyl-isomers become predominant (78, 83%, respectively).