Copper-catalyzed [3 + 2] annulation of ethynyl epoxides with malononitrile to access highly substituted dihydrofurans with an all-carbon quaternary stereocenter

An unprecedented copper-catalyzed [3 + 2] annulation with ethynyl epoxides and malononitrile has been described. This reaction provided a direct approach to the access of highly substituted dihydrofurans with an all-carbon quaternary stereocenter bearing a terminal alkynyl group in moderate to good yields, exhibiting excellent atom economy and scalability. The products enabled facile transformations into pyrimidinone and dihydrofuran-fused triazole derivatives.