Upon irradiation at wavelengths above 390 nm in the presence of 2,3-dimethylbut-2-ene, both the newly synthesized pyranoquinolinedione 8 and thiinobenzopyrandione 9 selectively afford one of two possible photocycloadducts, 23 and 24, respectively.
Reaction of nitrosalicylaldehydes (1) with carbethoxymethylenetriphenylphosphorane in Et(2)NPh, in Ph(2)O, and in the absence of solvent (neat) at 210-215 degrees C was investigated. Reaction of 3-nitrosalicylaldehyde (1d) in Et(2)NPh afforded the benzoxazole (6) and the aminocoumarin (3e) along with the expected coumarin (3d). It was clarified that the origin of carbon-unit introduced for the formation of the benzoxazole ring came from the alkyl group of solvent.
Harayama Takashi, Nakatsuka Kazumitsu, Nishioka Hiromi, Murakami Kyoko, O+, Heterocycles, 38 (1994) N 12, S 2729-2738