Asymmetric Synthesis of 3,4-Diaminochroman-2-ones Promoted by Guanidine and Bisguanidium Salt

A highly enantioselective synthesis of 3,4-diaminochroman-2-ones has been realized via the domino reaction of o-hydroxy aromatic aldimines and azlactones. Notably, a cis-product was obtained as the major product by the use of guanidine 2a whereas a trans-product was the major product with bisguanidium salt 3•HBArF4. In two cases, various substituted 3,4-dihydrocoumarins were obtained with high yields (up to 99%) as well as excellent enantioselectivities (up to 99% ee) and diastereoselectivities (up to >99:1 cis:trans and 98:2 trans:cis, respectively) under mild reaction conditions.