RADICAL ANNULATIONS WITH NITRILES - NOVEL CASCADE REACTIONS OF CYANO-SUBSTITUTED ALKYL AND SULFANYL RADICALS WITH ISONITRILES

New radical annulation reactions are described involving addition of c yano-substituted alkyl and sulfanyl radicals to aromatic isonitriles. The tandem cyclisation of the resulting imidoyl radicals onto the cyan o group affords cyclopenta- and thienoquinoxalines, respectively. The intervention of the isonitriles in the aromatisation process of the cy ctohexadienyl radicals is discussed as well as the regiochemistry of t he cyclisation of the iminyl radicals obtained by addition of the imid oyls to the nitrile moiety. The hypothesis of an exclusive 6-membered ring closure onto the aromatic ring is also supported by the results o f semiempirical AM1 calculations. (C) 1998 Elsevier Science Ltd. All r ights reserved.