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. Gallium complexes with the functionally labile (redox‐active) bis‐amido ligand dpp‐bian serve well as catalysts for the hydroarylation of phenylacetylene. The product of the reaction between phenylacetylene and naphthalen‐1‐ol undergoes further a catalytic transformation to give chiral chromenes.