EFFECT OF RING STRAIN ON THE FORMATION AND PYROLYSIS OF SOME DIELS-ALDER ADDUCTS OF 2-SULFOLENE (2,3-DIHYDROTHIOPHENE 1,1-DIOXIDE) AND MALEIC-ANHYDRIDE WITH 1,3-DIENES AND PRODUCTS DERIVED THEREFROM

7-Thiabicyclo[4.3.0]non-3-ene 7,7-dioxide 3 and the 2,5-bridged analog ues 4-6 formed by Diets-Alder reaction of 2,3-dihydrothiophene 1,1-dio xide (2-sulfolene) 2 with butadiene and cyclic 1,3-dienes are found, u pon flash vacuum pyrolysis, either to lose SO2 and ethene, or to under go a retro-Diels-Alder reaction, depending an the degree of ring strai n present. The epoxides 10, 13 and 17 of these compounds decompose exc lusively by loss of SO2 and ethene to give the mono-epoxides of cyclic 1,4-dienes which undergo further reactions under the pyrolysis condit ions. The same final products can also be obtained by extrusion of CO and CO2 from the epoxides 12, 16 and 19 of the corresponding diene-mal eic anhydride adducts. In the case of the furan-maleic anhydride adduc t, its epoxide 20 fragments by a retro-Diels-Alder reaction to give 1. 4-dioxine, which, at high temperatures, is transformed into acrylaldeh yde. Pyrolysis of the aziridines 22-24, formed by photochemical reacti on of the diene-maleic anhydride adducts with ethyl azidoformate, gene rally gives complex decomposition products, although for the methylene -bridged compound 22 there is good evidence for the generation of a 1, 4-dihydropyridine via a retro-Diels-Alder reaction.