Synthesis of topologically constrained naphthalimide appended palladium(ii)-N-heterocyclic carbene complexes - insights into additive controlled product selectivity

Topologically constrained naphthalimide appended Pd-NHCs were synthesized and characterized. These structurally related complexes were catalytically compared with previously synthesized Pd-NHCs in the regioselective heteroannulation of o-haloanilines and arylethynyl-trimethylsilane. The unique effect of an additive on product selectivity has been clearly demonstrated. The scope of the reaction with respect to different TMS protected alkynes and o-haloanilines is presented. Importantly, the step-economical regioselective synthesis of N-alkyl-3-aryl-indoles from o-haloanilines and arylethynyl-trimethylsilane assisted by Pd(ii)-NHCs has been clearly demonstrated via one-pot heteroannulation, TMS deprotection and N-alkylation. In addition, synthetic utility was demonstrated with several derivatizations.