Reactions of triphenylbismuthonium 2-oxoalkylides† with 1,2-dicarbonyl compounds

Abstract

Triphenylbismuthonium 2-oxoalkylides 2, generated in situ from bismuthonium salts 1 and a base in THF at low temperature, react with α-keto esters 3 and α-diketones 6 to give oxiranes 4 or 7 and/or O-aroyl enolates of unsymmetrical β-diketones 8, depending on the structures of substrates. Similar treatment of 2 with o-quinones 10 results in the ring expansion to 2-acyl-3-hydroxytropones 11. The enolates 8 and tropones 11 are most likely to be formed via the 1,2-carbon-to-oxygen and carbon-to-carbon migrations of the acyl group, respectively, both under simultaneous elimination of the triphenylbismuthonio group as bismuthine 5. Tropone 11c readily condenses with hydrazine hydrate to give a functionalized pyrazole 18.