Selectivity in Garratt–Braverman Cyclization of Aryl-/Heteroaryl-Substituted Unsymmetrical Bis-Propargyl Systems: Formal Synthesis of 7′-Desmethylkealiiquinone

Abstract

Unsymmetrical bis-propargyl ethers and sulfonamides containing various combinations of aryl/heteroaryl substituents at the acetylene termini were synthesized, and their reactivity under basic conditions was studied. Moderate to high (chemo)selectivity was observed, which followed a trend opposite to that reported earlier for the corresponding sufones. The major products obtained in most cases (except with indole) were formed via participation of the heteroaryl ring or the less electron rich aryl ring. The selectivity observed in imidazole-based systems was exploited to complete a formal total synthesis of 7'-desmethylkealiiquinone, an analogue of the marine alkaloid kealiiquinone.