Bifunctional Squaramide-Catalyzed Asymmetric Michael/Cyclization Reactions of 3-Hydroxychromenones with Isatylidenemalononitriles

A squaramide-catalyzed asymmetric Michael/cyclization tandem reaction between 3-hydroxychromenones and isatylidenemalononitriles was developed. Using this strategy, a wide scope of spiro[indoline-3,4′-pyrano[3,2-b]chromene] derivatives, which combined chromone, pyran, indolone in one molecule, could be obtained in moderate to excellent yields (up to 94 %) with moderate enantioselectivities (up to 95 % ee). In addition, the scaled-up experiment also confirmed the synthetic practicality of this synthetic strategy.