C-C coupling reaction of 1,5-dibromo-2,6-dihydroxynaphthalene with alakli 2-naphthoxide. Opposite effects of counterion coordination and hydrogen bonding on stereoselectivity in the formation of cis- and trans-1,1':5',1''-ternaphthyls

Article abstract of DOI:10.1016/0040-4020(96)00619-9

The title reaction yields cis- and trans-2,2',6',2''-tetrahydroxy-1,1':5',1''-ternaphthyls as the main products. In contrast to non-selective distribution of the stereoisomers in the thermodynamic equilibrium, very high selectivity can be attained under conditions of kinetic control. The observed values of cis-/trans- ratios range between the extremes 94:6 and 6:94, depending on the solvent and counterion employed. The coordination of the metal counterion plays a key role in the reaction performed in toluene, supporting formation of the cis-stereoisomer. When the coordination ability of the counterion is suppressed by 18-crown-6, intramolecular hydrogen bonding of the departing bromide group prevails in the stereocontrol, providing support for the trans-stereoisomer formation.