Ruthenium-Catalyzed Dimerization of 1,1-Diphenylpropargyl Alcohol to a Hydroxybenzocyclobutene and Related Reactions

Propargyl alcohol is a useful synthon in synthetic organic chemistry. We found that the ruthenium(II) complex [Cp*RuCl(diene)] (Cp* = η-C5Me5; diene = isoprene or 1,5-cyclooctadiene (cod)) catalyzes dimerization of 1,1-diphenylprop-2-yn-1-ol (1,1-diphenylpropargyl alcohol, 1a) at room temperature to afford an alkylidenebenzocyclobutenyl alcohol 2a quantitatively. Meanwhile, a stoichiometric reaction of the related hydrido complex [Cp*RuH(cod)] with 1a at 50 ◦C led to isolation of a ruthenocene derivative 4 bearing a cyclopentadienyl ring generated by dehydrogenative trimerization of 1a. Detailed structures of 2a and 4 were determined by X-ray crystallography. The reaction mechanisms for the formation of 2a and 4 were proposed.