Hydroarylation of Alkynes with Phenols in the Presence of Gallium Complexes of a Labile N-Ligand: Synthesis of Chromenes

In the presence of (dpp-bian)Ga-Ga(dpp-bian) (1) and [dpp-bian(Ph)C=C(H)]Ga-Ga[(H)C=C(Ph)dpp-bian] (2) {dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene}, phenylacetylene reacts with 1-naphthol to give 2-(1-phenylvinyl)naphthalen-1-ol (3). In solution in the presence of complexes 1 or 2, compound 3 undergoes further dimerization to give 2-[4-methyl-2,4-diphenyl-3,4-dihydro-2H-benzo[h]chromen-2-yl]naphthalen-1-ol (C36H28O2), whose diastereomers 4 and 5 were isolated in crystalline form. Diastereomer 4 is the kinetically favored product, which, however, undergoes conversion into diastereomer 5 in solution at elevated temperature. The structures of 4 and 5 were determined by single-crystal X-ray analysis. The catalytic activity of complexes 1 and 2 in the hydroarylation reactions of phenylacetylene and some other alkynes with different arenes has been investigated. By the reaction of phenylacetylene with 3,5-di-tert-butylphenol, 5,7-di-tert-butyl-4-methyl-2,4-diphenyl-4H-chromene (7) has been prepared for the first time.