Aromatic C–H insertion of β-phenoxyalkylidenecarbenes generated by reaction of alkynyl(p-phenylene)bisiodonium ditrifluoromethanesulfonates (ditriflates) with phenoxide anions

Abstract

Reaction of alkynyl(p-phenylene)bisiodonium ditriflates with sodium phenoxide in methanol provides 2-substituted benzofurans in 49–62% yields. This result indicates that β-phenoxyalkylidenecarbenes are generated by the reaction with phenoxide anion and undergo novel intramolecular aromatic C–H insertion to afford benzofurans. 2-Phenoxy-2-phenylethenylidene generated analogously in situ underwent competing processes of aromatic C–H insertion and 1,2-phenyl migration. The corresponding reactions with 4-substituted phenoxide ions also afforded 5-substituted benzofurans and, as the minor products, 2-aryloxy-1-iodoalk-1-enes which were probably derived from the intermediate vinyliodonium salts. Reactions of alkynyl(p-phenylene)bisiodonium ditriflates with sodium [²H₅]phenoxide (98% ²H) in methanol gave deuterated 2-alkylbenzofurans in 35–40% yields and the hydrogen at the 3-position of the benzofurans was deuterated completely. This result strongly supports selective aromatic C–H insertion of the in situ generated β-phenoxyalkylidenecarbenes.