Difluoro Carbenes: From Genuine Gold Complexes to Unprecedented Metallacyclic Reactivity.

Difluorocarbene is a very powerful synthon in organic chemistry, but its reactivity is very challenging to tame. While a few recent studies have pinpointed the potential of transition metals such as Pd and Cu to stabilize and harness difluorocarbene, known examples are confined to relatively classical transformations. Here we report gold(I) difluorocarbenes persisting for hours at 0 °C thanks to ligand-enhanced backdonation. These complexes exhibit unforeseen reactivity with alkenes and 1,3-dienes. The key intermediates, gold(III) metallacycles, have been spectroscopically and crystallographically characterized. Choosing the ligand at gold and operating conditions (thermal or photochemical) enable to direct C─C coupling to the desired product. This novel gold-mediated two-electron redox pathway was leveraged to prepare difluorocyclopentenes, overcoming the intrinsic challenge of [1+4] cycloaddition between carbenes and 1,3-dienes.