Enantioselective Synthesis of trans-Dihydrobenzofurans via Primary Amine-Thiourea Organocatalyzed Intramolecular Michael Addition

A primary amin Et-thiourea organocatalyzed intramolecular Michael addition access was developed for the synthesis of trans-dihydrobenzofurans. Under the catalysis of an (R,R)-1,2-diphenylethylamine derived primary amine-thiourea bearing a glucosyl scaffold, the corresponding trans-dihydrobenzofurans were obtained in high yields with excellent level of enantioselectivities (94 to >99% ee). Moreover, an in situ isomerization occurring at high temperature gave good to excellent trans/cis ratios as well (trans/cis: 84/16-96/4).