Photoaddition of 4(3H)-Quinazolinone Derivatives to Olefins : Effects of the 2-Substituent

Abstract

The photochemical behavior of 3-(3-butenyl)-4(3H)-quinazolinone (2a) and its 2-chloro(2b) and 2-trifluoromethyl derivatives (2c) was examined in methanol at a variety of wavelengths (254, 300, and 350 nm). The intramolecular 2+2 photoadducts (10 and 14) were obtained only when 2c and its higher methylene homologue (13) were irradiated. Though the 2-unsubstituted quinazolone (2a) was photostable, is 2-chloro derivative (2b) afforded the cyclized product (4) via homolytic fission of the C-Cl bond. An enhancement of the photocycloaddition reactivity of the C=N bond in the quinazolone ring by introduction of a trifluoromethyl group was also demonstrated by the formation of the intermolecular adducts from 2-trifluoromethyl-4(3H)-quinazolinone (1c) by irradiation in the presence of olefins. The reactions due to C-N bond fission of the azetidine ring in these adducts are also described. Finally, by utilizing photo-induced C-Cl bond fission as found in 2b, rutecarpine (26) was synthesized by irradiation of 2-chloro-3-[2-(indol-3-yl)ethyl]-4-(3H)-quinazolinone (25).