Transition metal- and oxidant-free [3 + 2] cyclization of azomethine imines utilizing vinylene carbonate as dual synthons

A transition metal- and oxidant-free C–C/C–N annulation of azomethine imines with vinylene carbonate as dual synthons under simple reaction conditions is described herein. Depending on the structure of azinium- N -imines, vinylene carbonate could serve as an ethynol and acetylene surrogate, which results in the formation of pyrazolo[1,5- a ]pyridine derivatives and pyrazolo[1,5- a ]pyridin-2-ol derivatives through [3 + 2] cyclization. Importantly, this mild system tolerates a diverse array of heterocyclic N -imines such as quinolinium and isoquinolinium salts with good functional group compatibility.