Catalytic Boracarboxylation of Alkynes with Diborane and Carbon Dioxide by an N‑Heterocyclic Carbene Copper Catalyst

By the use of an N-heterocyclic carbene copper­(I) complex
as a
catalyst, the boracarboxylation of various alkynes (e.g., diaryl alkynes,
aryl/alkyl alkynes, and phenylacetylene) with a diborane compound
and carbon dioxide has been achieved for the first time, affording
the α,β-unsaturated β-boralactone derivatives regio-
and stereoselectively via a borylcupration/carboxylation cascade.
Some important reaction intermediates were isolated and structurally
characterized to clarify the reaction mechanism.