Regioselectivity in C-H activation: reagent control in cyclometallation of 2-(1-naphthyl)-pyridine

2-(1-Naphthyl)-pyridine (1) possesses sp(2) C-H bonds in both the gamma- and delta-positions and is therefore a suitable substrate for studying the cyclometallation selectivity with different reagents and conditions. Such selectivity studies are reported. Based on deuterium-exchange experiments it is concluded that cycloruthenation with RuCl2(p-cymene) dimer is reversible with kinetic and thermodynamic preference for gamma-substitution. Electrophilic cycloborylation, on the other hand, shows unusual delta-substitution. The previously published cyclopalladation and cycloauration of the substrate was studied in detail and was shown to be irreversible; they proceed under kinetic control and give gamma- and delta-substitution for palladium and gold, respectively.