Synthesis of Acetylenes from Carboxylic Acid Derivatives Via β-Keto Sulfones

Mono- and disubstituted acetylenes 5 are synthesized from carboxylic acid derivatives via the readily accessible β-keto sulfones 3. Reaction of esters, acid chlorides, and nitriles with lithiated derivatives of alkyl aryl sulfones affords the β-keto sulfones 3, which are converted to the enol phosphates 4 via the sodium or potassium enolates (Y=OEt, NMe2) or with catalysis by 4-dimethylaminopyridine (Y=OPh). Reductive elimination of the enol phosphates 4 with sodium in liquid ammonia or sodium amalgam in tetrahydrofuran leads to the alkynes 5. This use of β-keto sulfones is also applied to the synthesis of cyclododecyne from cyclododecanone.