Efficient Access to Skipped Dienes and Trienes by Cobalt-Catalyzed Reductive Coupling of Alkynes and Allenyl Carbonates

Skipped dienes is one of the most prevalent motifs in vast array of natural products, medicinal compounds, and fatty acids. Herein, we disclose a straightforward one-step reductive protocol under Co/PC for the synthesis of diverse 1,4-dienes with excellent regio- and stereoselectivity. The protocol utilize allenyl carbonate as 1,3-butadiene surrogate and providing a synthetic tool to access skipped diene in one step with alkyne under dual-catalytic approach. Further, large variety of alkynes including terminal alkynes, propargylic alcohols and internal alkynes were employed. The homologation of natural terpenols into synthetic terpenols by iterative allylation of four-carbon allyl units resulted in bio-mimetic synthetic terpenes derived from propargylic alcohols. Under this approach the programmed skipped diene can be accessed with predictable stereochemistry and might be a useful synthetic method for targeted synthe-sis. The experimental studies, control experiments and detailed DFT studies revealed that the 1,3-diene generated in situ from allenyl carbonate, diisopropyl ammonium act as proton source, Co(II)-π-allyl species involved in the catalytic cycle and the mechanism proceed through Co(II)−Co(I)−Co(III) pathway.