2.5- dihydrothiophene-1,1 -dioxides quinodimethanes from

Cheletropic elimination of sulfur dioxide from benzo(c)-l,3-dihydrothiophene dioxide (8) was used as a route to c-quinodimethanes [550]. 

The thiophene ring system can be utilized as a synthetic scaffold for the preparation of nonthiophene materials as the sulfur moiety can be removed by reduction (desulfurization) or extrusion (loss of SO2). The extrusion of sulfur dioxide from 3-sulfolenes (2,5-dihydrothiophene 1,1-dioxides) give dienes (butadienes or o-quinodimethanes) that can be utilized to prepare six-membered rings by cycloaddition chemistry. For example, thermolysis of 3-sulfolene 120 provided tricyclic pyrazole 122 via an intramolecular cycloaddition of the o-quinodimethane 121 that results by extrusion of sulfur dioxide <00JOC5760>. Syntheses of 3-sulfolenes 123 and 124 <00S507> have recently been reported. 

Three main strategies have been employed for the prodnction of heterocyclic orffto-quinodimethanes a 1,4-elimination, the chelotropic loss of snlfur dioxide from a 2,5-dihydrothiophene S. iS -dioxide and the electrocyclic ring opening of a cyclobnteno-heterocycle each of these is illustrated diagramatically below. 

---