Diverse reactivity of isatin-based N,N′-cyclic azomethine imine dipoles with arynes: synthesis of 1′-methyl-2′-oxospiro [indene-1,3′-indolines] and 3-aryl-3-pyrazol-2-oxindoles†
The reaction of aryne with isatin-based N,N′-cyclic azomethine imine 1,3-dipole afforded 3,3-disubstituted oxindole bearing a pyrrolidine ring and a quaternary stereocenter in very good yield. In contrast, methyl substitution on the pyrrolidine ring of 1,3-dipole directed [3+2] cycloaddition with aryne gave a mixture of column separable diastereomers of the cycloadduct with moderate diastereoselectivity in excellent yield. A plausible reaction mechanism is provided. The experimental results were supported by DFT calculations. Furthermore, the synthesized 3,3-disubstituted oxindole was synthetically transformed to a 1,3-diyne derivative.