Palladium-Catalyzed Tail-to-Tail Reductive Dimerization of Terminal Alkynes to 2,3-Dibranched Butadienes

The palladium-catalyzed tail-to-tail reductive dimerization of terminal alkynes is described for the first time. Aromatic terminal alkynes bearing diverse and sensitive functional groups as well as aliphatic terminal alkynes are efficiently transformed to 2,3-dibranched butadienes. The key to achieve a selective tail-to-tail reductive dimerization reaction is to control appropriately the acidity of the reaction solution, which is accomplished by a combined use of pivalic acid and para-toluenesulfonic acid. The tail-to-tail reductive dimerization reaction is proposed to proceed via a cationic alkenyl palladium intermediate under acidic conditions.

Automated summary

A palladium-catalyzed tail-to-tail reductive dimerization reaction of terminal alkynes is reported for the first time, leading to the efficient transformation of aromatic and aliphatic alkynes into 2,3-dibranched butadienes. The control of reaction solution acidity, achieved by a combination of pivalic acid and para-toluenesulfonic acid, is crucial for the selective tail-to-tail reductive dimerization reaction, which is proposed to proceed via a cationic alkenyl palladium intermediate under acidic conditions.