title: Type-Two intramolecular diels-alder reactions of pyrazolo-o-quinodimethanes
abstract: Two isomeric series of homologous N-(acryloyloxy)alkylated pyrazolo-3-sulfolenes 10a-c and 18a-c have been efficiently synthesized from a common starting material, 4,6-dihydro-1H-thieno[3, 4-c]pyrazole (5). Thermolysis of these fused 3-sulfolenes provides the corresponding o-quinodimethanes which simultaneously undergo "type-two" intramolecular Diels-Alder reactions to form two- and three-atom-bridged tricyclic pyrazoles which are otherwise difficult to prepare. It was also demostrated that, depending on the N-substitution position of the pyrazolo-fused 3-sulfolenes, the temperature required for the thermal extrusion of SO(2) and the regioselectivity of the T2-IMDA reactions were influenced substantially.
authors.affiliation: Institute of Chemistry, Academia Sinica, Taipei, Taiwan 115, Republic of China.
authors.initials: Ts
authors.lastname: Chou
authors.initials: HC
authors.lastname: Chen
authors.initials: WC
authors.lastname: Yang
authors.initials: WS
authors.lastname: Li
authors.initials: I
authors.lastname: Chao
authors.initials: SJ
authors.lastname: Lee