[4+2] Cycloaddition of Ketenes with N‐Benzoyldiazenes Catalyzed by N‐Heterocyclic Carbenes

Enantioselectivity switch: A catalytic enantioselective [4+2] cycloaddition reaction of alkylarylketenes with N-aryl-N′-benzoyldiazenes or N,N′-dibenzoyldiazenes to give 1,3,4-oxadiazin-6-ones 1 was developed by employing N-heterocyclic carbene (NHC) catalysts. The enantioselectivities could be switched for most reactions by changing the substituents on the NHC catalyst. TBS=tert-butyldimethylsilyl, Mes=2,4,6-trimethylphenyl.