T. Shimo et al., PHOTOCHEMICAL BEHAVIOR OF 4-(OMEGA-ENYL)-2-PYRONES AND 4-(OMEGA-DIENYL)-2-PYRONES, Journal of heterocyclic chemistry, 32(1), 1995, pp. 341-345
4-(omega-Enyl)-2-pyrone 3 and two types of 4-(omega-dienyl)-2-pyrones
4-6, 9 and 10 were prepared and the photochemical behavior was investi
gated. Photosensitized reaction of 3 afforded [2+2]-cycloadduct 11 sit
e-specifically. On the other hand, 4 and 5 gave geometrical isomers, r
espectively. 2-Pyrones 6, 9 and 10 possessing pendant furans gave no a
dduct. The reasons for the differences are described.