Convergent Synthesis of 1,4-Dicarbonyl Z -Alkenes through Three-Component Coupling of Alkynes, α-Diazo Sulfonium Triflate, and Water.

We report a general protocol for the convergent synthesis of 1,4-dicarbonyl Z -alkenes form alkynes using α-diazo sulfonium triflate and water. The C═O, C═C, and C-H bonds are formed under mild conditions with a wide range of functional groups tolerated. The reaction exhibits excellent Z -selectivity and complete regioselectivity. The resulting 1,4-dicarbonyl Z -alkenes can smoothly undergo follow-up conversion to a variety of heteroaromatic scaffolds. Moreover, the reaction also provides a facile access to the corresponding deuterated Z -alkenes and deuterated heteroarenes with a high level of deuterium incorporation (90-97% D-inc.) by directly using D 2 O, thus rendering the method highly valuable. The comprehensive mechanistic studies indicate that a free carbyne radical intermediate is formed via the photocatalytic single electron transfer process, and KH 2 PO 4 plays a crucial role in significant improvements on yield and selectivity based on density-functional theory calculations, providing a new direction for radical coupling reactions of diazo compounds.