SYNTHONS FOR THE PARENT VINYL CARBENE COMPLEX IN THE BENZANNULATION REACTION

The benzannulation reaction of Fischer carbene complexes with alkynes to produce phenols was found not be synthetically useful for the paren t vinyl carbene complex 6a. The beta-silylated vinyl carbene complex 6 c is more stable than the parent vinyl complex 6a and can be effective ly used as a synthon for 6a since during the benzannulation the silico n migrates to the phenol function preferentially over hydrogen to give the arene chromium tricarbonyl complexes of the type 19. This reactio n is general for a number of alkynes that have incorporated important functionality and is more useful for terminal alkynes than for interna l alkynes. The migration of the silicon is responsible for the fact th at stable arene chromium tricarbonyl complexes can be isolated from th ese reactions and makes possible transformations that take advantage o f the activating ability of the chromium tricarbonyl group. This is de monstrated in intramolecular aromatic nucleophilic additions reactions . It is also shown in a single example that the alpha-silylated vinyl carbene complex 10b can in principle also serve as a synthon for the p arent vinyl carbene complex 6a, since the benzannulated product can be disilylated with trifluoroacetic acid.