Asymmetric Sequential Michael Addition and Cyclization Reactions of 2-(2-Nitrovinyl)phenols Catalyzed by Bifunctional Amino-Squaramides

In this work, we describe the Michael addition-cyclization reaction of 2-(2-nitrovinyl)phenol with two different reactive Michael donors, which lead to chiral benzopyran derivatives. Specifically, bifunctional amino-squaramides with one or two chiral units in the side chains were evaluated as catalysts in these transformations. Furthermore, the utility of selected green solvents as reaction media for these processes was also tested. The best result was achieved with methyl-cyclopentanone-2-carboxylate as the Michael donor in ethyl (-)-L-lactate with quinine-based amino-squaramide as catalyst (yield 72%, dr >99:1, ee 99%).

Automated summary

This study involved the Michael addition-cyclization reaction of 2-(2-nitrovinyl)phenol with two different reactive Michael donors to produce chiral benzopyran derivatives. Bifunctional amino-squaramides containing one or two chiral units were evaluated as catalysts, and the use of green solvents as reaction media was investigated. The best result was achieved using methyl-cyclopentanone-2-carboxylate as the Michael donor in ethyl (-)-L-lactate with a quinine-based amino-squaramide catalyst.