Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine-quinolizinium conjugates

Phil M Pithan; Sören Steup; Heiko Ihmels

doi:10.3762/bjoc.16.82

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine-quinolizinium conjugates

Beilstein J Org Chem. 2020 May 5:16:904-916. doi: 10.3762/bjoc.16.82. eCollection 2020.

Authors

Phil M Pithan¹, Sören Steup¹, Heiko Ihmels¹

Affiliation

¹ Department of Chemistry and Biology, University of Siegen and Center of Micro- and Nanochemistry and Engineering (Cμ), Adolf-Reichwein-Str. 2, 57068 Siegen, Germany.

Abstract

Two new spiroindolinonaphthoxazine derivatives with an electron-accepting styrylquinolizinium or styrylcoralyne unit, respectively, were synthesized, and the influence of such an arylvinyl substituent on the chemical and photochemical properties of the compounds was investigated. Specifically, these spirooxazines turned out to be resistant towards the photoinduced merocyanine formation, and the irradiation with light mainly led to photodegradation of the substrates. However, it was shown by colorimetric and fluorimetric screening assays as well as by detailed NMR spectroscopic and mass spectrometric studies that the addition of particular metal ions (Cu²⁺, Fe³⁺, and to a certain extent Hg²⁺) initially induced a ring-opening reaction that was irreversibly followed by a fast ring closure-deprotonation-oxidation sequence to give styryl-substituted naphthoxazole derivatives as the products quantitatively. For the quinolizinium-substituted spirooxazine derivative, the formation of the respective oxidation product caused the development of a broad absorption band between 425 nm and 500 nm and a new emission band at λ_fl = 628 nm, so that it may be employed as a selective chemosensor or chemodosimeter for the colorimetric and fluorimetric detection of Cu²⁺ and Fe³⁺.

Keywords: oxazole; oxidation; quinolizinium; spirooxazines; styryl dyes.

Grants and funding

PMP thanks the Fond der Chemischen Industrie for a PhD fellowship. Financial support by the Deutsche Forschungsgemeinschaft and the University of Siegen is gratefully acknowledged.