Efficient Asymmetric Synthesis of 4H-Chromene Derivatives through a Tandem Michael Addition-Cyclization Reaction Catalyzed by a Salen-Cobalt(II) Complex

The asymmetric synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene derivatives was achieved through a tandem Michael addition-cyclization reaction of easily available cyclohexane-1,3-dione and ethyl 2-cyano-3-phenylacrylates. Moderate to good yields (up to 81 %) and high enantioselectivities (up to 89 % ee) were obtained with a chiral salen-cobalt(II) complex. This process was air tolerant and easily performed, which provides an efficient method for the synthesis of chiral 4H-chromene derivatives.