Spectroscopic, computational and mechanistic studies on regio- and stereoselectivity of the 1,3-dipolar cycloaddition reaction in the synthesis of dispiro[indoline-3,2′-pyrrolidine-3′,3"-indolines] festooned with pyrene moiety

An efficient and catalyst-free multicomponent sequence for synthesizing fused new polyheterocyclic pyrene-grafted dispiro-pyrrolidine oxindolines through 1,3-dipolar cycloaddition reaction mediated by non-stabilized azomethine ylides is reported herein. The regio- and stereochemistry of the cycloadducts were determined on the basis of one-dimensional (1D) and two-dimensional (2D) homonuclear and heteronuclear correlation NMR spectroscopy. The mechanism of the cycloaddition reaction, as well as regioselectivity were discussed by evaluating global and local electrophilicity and nucleophilicity descriptors at B3LYP/6-31G level of theory. The findings suggested that the polarity and charge transfer flow between azomethine ylides (dipole) and 5-chloro-3-(2-oxo-2-(pyren-1-yl)ethylidene)indolin-2-ones (dipolarophiles) was consistent with the global reactivity descriptors and substitutional pattern. These outcomes based on local descriptors Parr functions proposed by Domingo were found to be quite promising indices for the study of organic reactivity and to explain the regioselectivity of cycloaddition processes.