PhPCN: A stable reagent for carbon-atom transfer.

Precise modification of a chemical site in a molecule at the single-atom level is one of the most elegant yet difficult transformations in chemistry. A reagent specifically designed for chemoselective introduction of monoatomic carbon is a particularly formidable challenge. Here, we report a straightforward, azide-free synthesis of a crystalline and isolable diazophosphorus ylide, PhPCN, a stable compound with a carbon atom bonded to two chemically labile groups, triphenylphosphine (PPh) and dinitrogen (N). Without any additives, the diazophosphorus ylide serves as a highly selective transfer reagent for fragments, including PhPC, to deliver phosphorus ylide-terminated heterocumulenes and CN to produce multisubstituted pyrazoles. Ultimately, even exclusive carbon-atom transfer is possible. In reactions with aldehydes and acyclic and cyclic ketones (RC=O), the carbon-atom substitution forms a vinylidene (RC=C:) en route to alkynes or butatrienes.