New isoindigoide dyes from heterocyclic 2,3-diones - Synthesis and thermal rearrangement

Article abstract of DOI:10.1016/0040-4020(96)00173-1

The heterocyclic 2,3-diones 1 and 11 together with Lawesson reagent (LR) afford novel isoindigoide dyes 4 and 12, respectively. 4a can thermally be isomerized into the pyrano[4,3-c]pyrane 6, accompanied by a significant hypsochronic shift which was corroborated by quantum chemical calculations. The phosphoranylidene derivative 13 was obtained via Wittig reaction of 1. All structural assignments were based on X-ray studies of 4a and 13.