Palladium-Catalyzed C-C Bond Activation and Regioselective Alkenyla-tion between Cyclopropanol and 1,3-Diyne: One-Step Synthesis of Di-verse Conjugated Enynes

We report here the first example of the use of 1,3-dialkynes in C-C bond activation with any metal. The regio- and stereo-selective synthesis of 1,3-enynes from 1,3-diynes is demonstrated by the palladium-catalyzed C-C bond activation of cyclo-propanol. Exclusive formation of mono-alkenylated adduct was achieved by eliminating the possibility of di-functionalization with high regio- and stereo-selectivity. Indeed, this protocol worked very well with electronically and sterically diverse substrates. Several studies, including deuterium labeling experiments and intermolecular competitive experiments, were carried out to understand the mechanistic details. The atomic-level mechanism followed in the catalytic process was also validated using DFT calculations, and the rate-controlling states in the catalytic cycle were identified. Further, preliminary mechanistic investigations with radical scavengers revealed non-involvement of the radical pathway for this transformation.