Conjugated dienes and polyenes are typically synthesized by sequential introduction of C═C bonds. Here, we report a practical and scalable, catalytic dienylation that is highly regio- and stereoselective for both C═C bonds. The reaction is enabled by a stereoselective palladium-catalyzed cross-coupling that is preceded by a regioselective base-induced ring opening of readily available sulfolenes. The dienylation reaction is particularly useful for the synthesis of synthetically challenging dienes containing cis double bonds. We also show that the reaction can serve as a synthetic platform for the construction of conjugated polyenes.

Conjugated dienes and polyenes are central structural motifs of natural products, and key synthetic intermediates in organic synthesis and materials science. We describe herein a palladium-catalyzed dienylation of aryl, heteroaryl, and vinyl triflates, nonaflates and iodides that were previously identified as recalcitrant substrates for the sulfolene-mediated catalytic dienylation. The method has now been successfully expanded to CO and C-I dienylation, demonstrating broad scope with respect to sulfonates, iodides and sulfolenes. The reactions proceed with high regio-and stereoselectivity, and efficiency that are strongly influenced by basic additives, whose influence on the reaction performance was systematically studied.

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To date, no CCC‐NHC pincer complexes of Re have been reported in the literature. The first CCC‐NHC pincer complex of Re is reported. It was fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy, elemental analysis, and X‐ray crystallographic methods to determine the molecular structure. It was synthesized via transmetallation from an isolated Zr precursor and was found to be air stable. The catalytic activity of the CCC‐NHC Re(I) pincer complex was demonstrated for the borrowing hydrogen coupling reaction between benzylic ketones and primary alcohols to generate a new C–C bond in an environmentally friendly catalysis requiring no activating groups for the alcohol functionality. This borrowing hydrogen coupling reaction produced a stoichiometric amount of water as the only by‐product and did not require the conversion of the primary alcohol to a leaving group. A broad range of substrates was examined, and isolated yields from 53% to 92% were obtained. A catalytic cycle for the CCC‐NHC Re(I) pincer complex catalyzed borrowing hydrogen coupling reaction is proposed.