Synthesis of optically active 2-amino-1′-benzyl-2′,5-dioxo-5H-spiro[indeno[1,2-b]pyran-4,3′-indoline]-3-carbonitriles catalyzed by a bifunctional squaramide derived from quinine

The first organocatalytic asymmetric reaction of propylene malononitrile with oxoindole and 1,3-indandione for the synthesis of chiral indeno-spiro compounds has been developed. Under bifunctional squaramide catalysis, a wide range of optically active 5H-spiro[indeno[1,2-b]pyran-4,3′-indoline] derivatives were obtained in excellent yields (up to 95%) with moderate to good enantioselectivities (up to 82%). Enantioselectivities of 90–99% were achieved through a simple recrystallization procedure for most products. These indeno-spiro compounds are promising candidates for drug discovery and biochemistry.