Reaktionen vinyloger Oxycarbene mit Methanol

Reactions of Vinylogous Oxycarbenes with Methanol The carbenes 16 and 30 were generated in methanol/sodium methoxide by photolyses of 2‐methylchromone tosylhydrazone ( 14 ) and 3,5‐dimethoxy‐4,4‐dimethyl‐2,5‐cyclohexadienone tosylhydrazone ( 28 ), respectively. Neither 16 nor 30 accept methanol at the carbenic site to give products of a formal O – H insertion. Carbene 16 affords 2‐methoxy‐2‐methyl‐2 H ‐1‐benzopyran ( 19 ) by way of the benzopyrylium ion 17 . The same ether was obtained from the independently prepared perchlorate of 17 . Protonation of 30 was followed by demethylation of the delocalized carboxonium ion 31 to give 5‐methoxy‐6,6‐dimethyl‐2,4‐cyclohexadienone ( 33 ) as the only product.