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‐2 H ‐benzo[ h ]chromen‐2‐yl]naphthalen‐1‐ol (C 36 H 28 O 2 ), 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‐4 H ‐chromene ( 7 ) has been prepared for the first time.