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

Reaction of alkynyl(p-phenylene)bisiodonium ditriflates with sodium phenoxide in methanol provides 2-substituted benzofurans in 49-62% yields, This result indicates that beta-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 [H-2(5)]phenoxide (98% H-2) 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 beta-phenoxyalkylidenecarbenes.