Cobalt-induced synthesis of 6-(pyridin-2-yl)purines by microwave-enhanced [2+2+2] cyclotrimerization

A novel, efficient, and atom-economic methodology for the preparation of a large series of diversely substituted (pyridin-2-yl)purines has been developed. Thus, microwave-enhanced [2+2+2] cyclotrimerization of 6-(diynyl)purines with nitriles in the presence of a stoichiometric or catalytic amount of [CpCo(CO)(2)] afforded the corresponding products in good yields. The reactions carried out with various alkyl, aryl, and heteroaryl cyanides poceeded with exclusive regioselectivity, affording 6-(pyridin-2-yl)purines. In an analogous manner, [2+2+2] cyclotrimerizations of 1,8-bis(purinyl)-1,7-octadiynes with nitriles were conducted, yielding 1,4-bis(purin-6-yl)5,6,7,8-tetrahydroisoquinolines. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).