A. Goswami, Kazuhiko Ohtaki, Kouki Kase
Jan 4, 2008
Citations
0
Influential Citations
50
Citations
Journal
Advanced Synthesis & Catalysis
Abstract
A variety of substituted 2,2'-bipyridines were synthesized by a 1,2-bis(diphenylphosphino)-ethane (dppe)/cobalt chloride hexahydrate (CoCl 2 .6 H 2 O)/zinc-catalyzed [2+2+2] cycloaddition reaction of diynes and nitriles, with all reactions exhibiting exclusive regioselectivity. Thus, symmetrical and unsymmetrical 1,6-diynes and 2-cyanopyridine reacted in the presence of 5 mol % of dppe, 5 mol % of CoCl 2 ·6H 2 O and 10 mol % of zinc powder to provide the corresponding 2,2'-bipyridines. Under identical reaction conditions, 1-(2-pyridyl)-1,6-diynes and nitriles reacted smoothly with exclusive regioselectivity to produce 2,2'-bipyridines in good yield. 2,2'-Bipyridines were also obtained by the double [2+2+ 2] cycloaddition reaction of 1,6,8,13-tetraynes with nitriles. Similarly, 2,2':6',2"-terpyridines were synthesized from 1-(2-pyridyl)-1,6-diyne and 2-cyanopyridine. The regiochemistry observed can be explained by considering the electronic nature of cobaltacyclopentadiene intermediates and nitriles. A survey of the exclusive regiochemical trend gives reasonable credence to the synthetic potential of the present method.