72350-06-2Relevant articles and documents
Photochemistry of 3-Alkylated and 3-Phenylated Oxepin-2(3H)-one Derivatives
Hoshi, Nobuto,Sato, Kazuhiro,Uda, Hisashi,Hagiwara, Hisahiro
, p. 3501 - 3596 (2007/10/02)
The direct and triplet-sensitized photochemistry of the 3,3-dimethyl- (1), 3-isopropyl- (9), 3-methyl-3-phenyl- (15a), and 3-phenyl- (15b) oxepin-2(3H)-one derivatives has been studied.All derivatives underwent, upon direct irradiation, competitively decarbonylation and cyclisation to give the conjugated dienal derivatives (7), (8), (11), (16), (17), and (36) and the 2-oxabicyclohept-6-en-3-one derivatives (2), (12), (13), (18), and (19).The triplet-sensitization of the 3-alkylated oxepinones (1) and (9) by methyl 2-naphthyl ketone gave rise exclusively to the cyclisation products (2), (12), and (13).In the case of (9), it was shown that heating a solution of (9) at 82 deg C produced and equilibrating mixture (ca. 3.6 : 1) of (9) and the fully conjugated 2(7H)-isomer (10), and irradiation at this temperature with >300 nm light led selectively to the isomeric cyclobuteno-lactone derivative (14), the cyclisation product of (10).In contrast, it was found that the triplet-sensitized photolysis of the 3-phenylated oxepinones (15) in neutral media proceeded through a completely different reaction pathway, phenyl-shifting rearrangements, giving rise to the 7-phenyl-2-oxabicyclohept-4-en-3-one derivatives (20) and (21) as together the major product, 5-phenyloxepin-2(5H)-one derivatives (22), 4-methyl-1-phenyl-2-oxabicyclohept-6-en-3-one (23), and 2-phenyl-3-oxabicyclohept-6-en-4-one (37).No photocyclisation of (15) could be detected.When the sensitized photoreaction of (15) was conducted in acidic methylene dichloride, only the 5-styrylfuran-2(5H)-one derivatives (44) and (45) were obtained.Any of the photoproducts from the reaction in neutral media could not be detected.Products were identified on the basis of spectral data and chemical transformations or alternative syntheses.From the results, the 1,5-phenyl shifted compounds, the 7-phenyloxepin-2(7H)-one derivatives (40), have been proposed as the initial sensitized photoproducts of (15) and proved definitely by the synthesis and reactions of (40), and finally by the actual isolation of (40a) from the photoreaction of (15a) in acetone at -78 deg C.Thus, it has been clarified that, from (40), the di-?-methane rearrangement leads to (20) and (21), the photocyclisation leads to (37), the thermal 1,5-hydrogen shift and the subsequent photocyclisation leads to (23), and the acid-promoted translactonisation leads to (45), and that the products (22) arise from (20) and/or (21) by reverse di-?-methane rearrangement.
