Reaction of an α-Methylpyrrole with Thionyl Chloride. an Unusual Synthesis of Pyrrole α-Thiocarboxamides.

Abstract A number of recent reports has described the thionyl chloride mediated oxidation of methylene groups activated by adjacent πaccepting functions. The reaction can follow several pathways according to the structure of the substrate and the amount of thionyl chloride used1. In the presence of excess thionyl chloride and a catalytic amount of a tertiary amine a Pummerer-type rearrangement2a leads to α - chlorosulphenyl chloride derivatives of carboxylic acids2,3 and ketones1,4. Similarly, 2-methylbenzoxazole and 2-methylbenzothiazole are oxidised to their α-chlorosulphenyl chloride derivatives4b.