Cycloaddition reactions between 3-vinylthiophen and the dienophiles maleic anhydride, methyl acrylate, dimethyl acetylene-dicarboxylate, and methyl propiolate give products including methyl benzo [b] thiophen-7-carboxylate (11) and its dihydroderivative (10), the 6, 7-dicarboxylic acid (3), its dimethyl ester (7) and dihydroester (6); the naphtho [a, b] dithiophen (14), and the novel ethano bridged benzo [b] thiophen (15).
![dimethyl 4,5-dihydrobenzo[b]thiophen-6,7-dicarboxylate Structure](https://image.chemsrc.com/caspic/168/110449-92-8.png)
