Type-two intramolecular Diels-Alder reactions of pyrazolo-o-quinodimethanes

Two isomeric series of homologous N-(acryloyloxy)alkylated pyrazolo-3-sulfo lenes 10a-c and 18a-c have been efficiently synthesized from a common start ing material, 4,6-dihydro-1H-thieno[3,4-c]-pyrazole (5). Thermolysis of the se fused 3-sulfolenes provides the corresponding o-quinodimethanes which si multaneously undergo "type-two" intramolecular Diels-Alder reactions to for m two- and three-atom-bridged tricyclic pyrazoles which are otherwise diffi cult to prepare. It was also demostrated that, depending on the N-substitut ion position of the pyrazolo-fused 3-sulfolenes, the temperature required f or the thermal extrusion of SO2 and the regioselectivity of the T2-IMDA rea ctions were influenced substantially.