Enantioselective synthesis of 7H-pyrano[2,3-d]thiazoles via squaramide-catalyzed [2+4] annulation of malononitrile and 5-ylidenethiazol-4-ones
摘要:
An efficient catalytic asymmetric synthesis of 7H-pyrano[2,3-d]thiazoles has been developed on the basis of the organocatalyzed [4+2] annulation of malononitrile and 5-ylidenethiazol-4-ones. Under the catalysis of a bifunctional squaramide derived from L-tert-leucine, the reaction of malononitrile and a wide range of 5-ylidenethiazol-4-ones ran smoothly to afford the corresponding structurally diverse 7H-pyrano[2,3-d]thiazole derivatives in good yields (70-94%) and with moderate to excellent enantioselectivities (43->99% ee). (C) 2016 Elsevier Ltd. All rights reserved.