Tautomeric-Dependent Lactam Cycloaddition with Nitrile Oxide: Facile Synthesis of 1,2,4-Oxadiazole4,5- a indolone Derivatives

摘要

A concise, metal-free, and gram-scale strategy to convert indoline-2,3-diones to 1,2,4-oxadiazole4,5-a indolones through an improved 3 + 2 cycloaddition of α-ketone-lactam with nitrile oxides has been developed. The lactim form of the resonance structure of isatin in protic solvents is the key active dipolarophile that shows chemo- and regioselectivity under experimental and theoretical conditions. This strategy conveniently enabled the assembly of several 1,2,4-oxadiazole4,5-a indolines with a broad range of functional groups. Compounds 3a and 4b exhibit cytotoxicity in the NCI/ADR-RES, SKOV3, and OVCAR8 cell lines.