Dealkenylative Alkynylation Using Catalytic Fe and Vitamin C.

In this paper, we report the synthesis of alkyl-tethered alkynes through ozone-mediated and Fe-catalyzed dealkenylative alkynylation of unactivated alkenes in the presence of alkynyl sulfones. This one-pot reaction, which employs a combination of a catalytic Fe salt and l-ascorbic acid, proceeds under mild conditions with good efficiency, high stereoselectivity, and broad functional group compatibility. In contrast to our previous Fe-mediated reductive fragmentation of α-methoxyhydroperoxides, the Fe-catalyzed process was devised through a thorough kinetic analysis of the multiple competing radical (redox) pathways. We highlight the potential of this dealkenylative alkynylation through multiple post-synthetic transformations and late-stage diversifications of complex molecules, including natural products and pharmaceuticals.