HFIP-Promoted Friedel-Crafts Allenylation of Imidazopyridines with Propargyl Alcohols at Room Temperature.

Herein, we report an efficient synthetic protocol for the Friedel-Crafts reaction of imidazo[1,2-]pyridines with propargyl alcohols in HFIP. Notably, this FC allenylation works without any additional solvent or catalyst and requires neither inert conditions nor heating. In this method, HFIP, besides offering hydrogen bonding with propargyl alcohol, also stabilizes the resultant carbocation, thus forming the product. This method also enables the straightforward synthesis of 1,3-enynes. The current method offers a large substrate diversity with good to excellent yields. We also demonstrated gram-scale synthesis and synthetic modifications.