Reductive coupling of allenyl/allyl carbonate with alkyne under dual cobalt-photoredox catalysis

Skipped dienes are among the most prevalent motifs in a 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 employs allenyl or allyl carbonate as π-allyl source, allowing for the direct synthesis of skipped diene with a broad range of alkynes including terminal alkynes, propargylic alcohols, and internal alkynes. The method also demonstrated the biomimetic homologation of natural terpenols into synthetic counterparts via iterative allylation of three-carbon allyl units, employing propargylic alcohol as a readily available alkyne source. Experimental studies, control experiments, and DFT calculations suggest the dual catalytic process generates 1,3-diene from allenyl carbonate, followed by proton and electron transfer leading to Co(II)-π-allyl species prior to the alkyne coupling. The catalytic cycle transitions through Co(II), Co(I), and Co(III). Skipped dienes are among the most prevalent motifs in vast array of natural products, medicinal compounds, and fatty acids. Here, the authors disclose a straightforward one-step reductive protocol under Co/PC for the synthesis of diverse 1,4-dienes with excellent regio- and stereoselectivity.