Synthons for the Parent Vinyl Carbene Complex in the Benzannulation Reaction

Article abstract of DOI:10.1021/jo00090a024

The benzannulation reaction of Fischer carbene complexes with alkynes to produce phenols was found not be synthetically useful for the parent vinyl carbene complex 6a.The β-silylated vinyl carbene complex 6c is more stable than the parent vinyl complex 6a and can be effectively used as a synthon for 6a since during the benzannulation the silicon migrates to the phenol function preferentially over hydrogen to give the arene chromium tricarbonyl complexes of the type 19.This reaction is general for a number of alkynes that have incorporated important functionality and is more useful for terminal alkynes than for internal alkynes.The migration of the silicon is responsible for the fact that stable arene chromium tricarbonyl complexes can be isolated from these reactions and makes possible transformations that take advantage of the activating ability of the chromium tricarbonyl group.This is demonstrated in intramolecular aromatic nucleophilic additions reactions.It is also shown in a single example that the α-silylated vinyl carbene complex 10b can in principle also serve as a synthon for the parent vinyl carbene complex 6a, since the benzannulated product can be disilylated with trifluoroacetic acid.