Benzannulation and N‐Annulation of β‐Ketoenamines for Synthesizing Aniline and Pyridine Derivatives Using DMSO as a Methine Source

Benzannulation and N-annulation of beta-ketoenamines by the in-situ generated methyl(methylene)sulfonium ion from the reaction of dimethyl sulfoxide (DMSO) and 1,2-dibromoethane (DBE) was achieved. The beta-ketoenamines underwent N-annulation to pyridine derivatives, while the N-alkylated enamines were benzannulated to afford substituted anilines. The utility of the intermediate methyl(methylene)sulfonium ion was further extended for synthesizing methylene-bridged bis-1,3-dicarbonyl compounds.