SYNTHESIS OF 1-FORMYLAZULENE DERIVATIVES AND ABSORPTION-SPECTRA OF NEW AZOMETHINE DYES CONTAINING AN AZULENE RING

Ethyl 1-formyl-2-hydroxyazulene-3-carboxylate (2a) was readily obtaine d in high yield from ethyl 2-hydroxyazulene-1-carboxylate (1a) using t he Vilsmeier reagent. Ethyl 5-isopropyl- and isopropyl-1-formyl-2-hydr oxy-azulene-3-carboxylate (2b and 2c) were isolated and their structur e confirmed by H-1 NMR spectra. Additionally, bromination and nitratio n of 2a was carried out to introduce a functional group into the seven -membered ring, to give 6-substituted 1-formylazulene derivatives. Abs orption spectra of azomethine dyes derived from these 1-formylazulene derivatives were significantly influenced by substituents. PPP-MO (Par iser-Parr-Pople Molecular Orbital) calculations indicated that the ori gin of these absorption bands was an intramolecular charge-transfer fr om the azomethine component to the azulene ring.