CYCLOADDITIONS .23. THE THERMAL REACTIVITY OF S-(1-NAPHTHYL) AND S-(9-ANTHRYL)2-METHYL-2,3-BUTADIENETHIOATES

Heating of the S-(1-naphthyl)esters of 2-methyl-2,3-butadiene thioacid and of 2-methyl-4,4-dipheny1-2,3-butadiene thioacid (3a resp. 3b) furnishes mixtures of the Diels-Alder products 5a, b and the cyclobutenone 7 and the naphthol derivative 8, resp. The corresponding S-(9-anthryl) esters 4a, b are not isolable; under the conditions of their synthesis (allenecarboxylic acids la u. b, 9-thioanthrol 2b, DCC and DMAP) they isomerise spontaneously to the Diels-Alder products 9.