Studies on the photocyclization reaction of 8‐styryl‐substituted coralyne derivatives

Abstract

The photoreactivity of four 8‐styryl‐substituted coralyne derivatives was examined by UV/VIS‐ and 1H‐NMR‐spectroscopy. Except for the dimethylamino‐substituted derivative, these cationic azoniaheterocyclic dyes undergo photocyclization that most likely proceeds through an initial E‐Z‐isomerization of the double bond. Subsequent oxidation of the intermediates under aerobic conditions gave the pyrrolo‐annelated quinolizinium derivatives as final products, thus providing a useful synthetic route to polycyclic azoniahetarene derivatives. The 6‐(4‐chlorophenyl)‐substituted pyrroloquinolizinium derivative was isolated on a preparative scale, and the investigation of its photophysical properties revealed significantly red‐shifted absorption (λabs = 465–480 nm) and emission bands (λfl = 550–562 nm) in comparison to the parent coralyne and the styryl‐substituted derivatives.

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

“…However, the irradiation of 3a at 420 nm caused a decrease of the absorption over the course of several hours, which pointed towards a gradual photodegradation of the substrate (Figure S2A, Supporting Information File 1). For 3b, the irradiation at 420 nm led to a decrease of the absorption and a bathochromic shift of the longwavelength absorption band, and after an irradiation time of 60 min, the spectrum showed distinct absorption bands with maxima at 463 nm and 325 nm (Figure S2B, Supporting Information File 1), which was in agreement with our recent finding that 8-styryl-substituted coralyne derivatives undergo a photocyclization-oxidation reaction upon irradiation under aerobic conditions to form pyrroloquinolizinium derivatives (Scheme S2, Supporting Information File 1) [70].…”