Treatment of ethyl and methyl phthalimidosulfanylacetate 1a and 1b with triethylamine at room temperature generates [eqn.(1)] the transient thioaldehydes, ethyl and methyl thioxoacetate 2, which have been trapped in situ with 2, 3-dimethylbuta-1, 3-diene to yield the Diels–Alder cycloadducts 8a and 8b in high yield. The cycloadducts 9, 10 and 11a and 12a of ethyl thioxoacetate 2a and anthracene, cyclohexa-1, 3-diene and cyclopentadiene, ...
