1,4‐Dehydrogenation with a Two‐Coordinate Cyclic (Alkyl)(amino)silylene

Cyclic (alkyl)(amino)silylene (CAASi) 1 has been found to successfully dehydrogenate 1,4‐dihydroaromatic compounds containing various substituents to afford the corresponding aromatic compounds. The observed high substrate generality proves 1 to be a potential 1,4‐dehydrogenation reagent for organic compounds. For the reaction with 9,10‐dimethyl‐9,10‐dihydroanthracene, silylene 1 activated not only benzylic C−H bonds but also aromatic C−H bonds to yield a silaacenaphthene derivative, which is an unprecedented reaction of silylenes. The results of the experimental and computational study of the reaction of CAASi 1 with 9,10‐dihydroanthracene and 1,4‐cyclohexadiene are consistent with the notion that 1,4‐dehydrogenation with CAASi 1 proceeds mainly through a stepwise hydrogen‐abstraction mechanism.