Intramolecular cyclization of 2-(o-carboran-1-yl) methylthio-3-cyanopyridines in basic conditions

Substituted 2-(o-carboran-1-yl)methylthio-3-cyanopyridines and -pyrimidines undergo Thorpe-Ziegler cyclization under the influence of KOH in DMF to give the corresponding thienopyridines and thienopyrimidines. The reaction is complicated by a side reaction in which the closo-carborane nucleus is converted to a nido-system. The yield of thienopyridines containing a closo-carborane unit is increased by introduction of an acceptor substituent in the pyridine ring. Destruction of the closo-carborane nucleus is not observed with the pyrimidine derivatives. The structures of the series of new carborane-containing thienopyridines and pyrimidines was confirmed by spectroscopic methods. ©1998 Plenum Publishing Corporation.