INTRAMOLECULAR REACTIONS OF FISCHER CARBENE COMPLEXES WITH ALKYNES AND A MECHANISTIC STUDY OF THE INTERCEPTION OF REACTIVE INTERMEDIATES WITH ADDED ACETYLENES

The reactions of 1-(4-hexynyl)methoxymethylenepentacarbonyl complexes 11 of the group 6 metals with alkynes lead to phenol and cyclopentenedione products, both of which are the result of cyclization with one molecule of the external alkyne and the internal alkyne in the carbene complex. All four of the possible phenol products of this reaction were independently synthesized, and the product distribution among the four isomers and the cyclopentenedione was investigated as a function of solvent, concentration, and the nature of the metal. The results of these experiments suggest that the phenol 13 arises from a vinyl carbene complexed intermediate and that the phenol 16 and cyclopentenedione 12 arise from a vinyl ketene complexed intermediate. This was confirmed by a series of methanol trapping experiments and by the isolation, characterization, and study of the chemistry of the proposed vinyl ketene complex.