An expedient and practical route for realizing a novel, substrate-controlled diastereoselective switch strategy has been successfully developed. The [4 + 1] annulation of thioamides with sulfur ylides proceeded smoothly via a Michael addition triggered sequential process, and trans-dihydrothieno [3,4-c] coumarins were obtained because of steric hindrance effects between the benzoyl group and the unit of 2Hchromen-2-one as shown in the Newman projection. Nucleophilic substitution was observed as the key step when the sulfur ylides were replaced with acetophenones in the [4 + 1] annulation, and a double p,p-stacking donor-acceptor interaction stabilized the transition state that led to the cis-dihydrothieno [3,4-c]coumarins. In addition, a facile chemoselective reaction was also investigated, providing a series of thieno [3,4-c]coumarins.

A one-pot synthesis of substituted (dihydro)thieno[2,3-c]chromene derivatives was developed through a Lewis base catalyzed domino Michael addition/intramolecular cyclization reaction between 3-nitro-2H-chromenes and thioamides. The desired (dihydro)thieno[2,3-c]chromene derivatives were prepared with a large substrate scope (22 examples) and excellent diastereoselectivity in moderate to excellent yields.