Dual Gold(I)‐catalyzed Cyclization of Dialkynyl Pyridinium Salts

Novel dialkynyl pyridines were synthesized and protected as alkyl salts for dual gold(I)‐catalyzed cycloisomerization. Different alkyl groups and counter ions were screened for the salts, with benzyl and hexafluorophosphate providing the best results. The cyclization led to NMR yields of >95 % being obtained for a number of substrates. Step‐wise hydrogenation of products could be performed in one‐pot by Pd/C, with selective reduction of the double bonds, followed by deprotection of the benzyl group. Gold the key to dialkynyl pyridines? A selection of novel dialkynyl pyridines was synthesized and cyclized into dihydropentalenopyridinium salts with NMR‐yields of 95 % and higher were obtained. The substitution pattern of the pyridine ring influenced the stability of the resulting salts. Step‐wise hydrogenation of products could be performed in one‐pot by Pd/C, with selective reduction of the double bonds, followed by deprotection of the benzyl group.