Abstract The condensation of thiotryptophol with β-ketoesters and successive hydrolysis of the intermediates afforded the title compounds which represent a novel ring system. The reaction of thiotryptophol with ethyl propiolate in the presence of sodium methoxide gave the unstable 1, 3, 4, 9-tetrahydrothiopyrano [3, 4-b] indole-1-acetic acid. One of the described products is the sulfur isoster of the potent antiinflammatory agent, prodolic acid. The sulfur ...