Efficient construction of diverse spiro[indoline-3,4'-pyrrolo[3,4- b ]pyridines] via [3 + 3] cycloaddition of MBH carbonates of isatins with β-enamino maleimides.

An efficient method to construct unique spiro[indoline-3,4'-pyrrolo[3,4- b ]pyridines] was successfully developed via a DABCO promoted formal [3 + 3] cycloaddition reaction of MBH carbonates of isatins with β-enamino maleimides in acetonitrile at room temperature. This reaction afforded multifunctionalized spiro[indoline-3,4'-pyrrolo[3,4- b ]pyridines] and spiro[dipyrrolo[3,4- b :3',4'- e ]pyridine-8,3'-indolines] in good yields and with lower diastereoselectivity. The relative configuration of the two diasteromers of the spiro compounds was clearly elucidated by the determination of eight single crystal structures.