One-Pot Synthesis of N-Fused Quinolone-4 Tetracyclic Scaffolds from 2,2-Disubstituted Indolin-3-ones

A cascade transformation of C2-quaternary indoxyls leading to an efficient assembly of complex (dihydro)indolo[1,2-a]quinolin-5-one ring systems is reported. The method involves the gram-scale preparation of 2-(2-aryl-3-oxoindolin-2-yl)-2-phenylacetonitriles which are then converted with methyl ketones to the corresponding 2-(2-oxo-2-aryl(alkyl)ethyl)-2-phenylindolin-3-ones. The latter can either be isolated with good yields (75–96%) or, in the case of o-nitroacetophenone, used in situ for further base-assisted intramolecular S_NAr cyclization resulting in indoxyl-fused quinolone-4 hybrids (up to 95%).