2158-24-9Relevant articles and documents
Photochemistry and spectroscopy of three α-oxo oxime ethers: 4-(methoxyimino)-2,2,3,3-tetramethylcyclobutanone, 3,3,5-trimethyl-4(5H)-isoxazolone and 6-(benzyloxyimino)-2,2,5,5-tetramethylcyclohexanone
Stunnenberg, Frank,Cerfontain, Hans,Geenevasen, Jan A. J.,Hielkema, Wim
, p. 31 - 40 (2007/10/02)
Following our previous reports on the spectroscopy and photochemistry of methyl and ethyl ethers of simple acyclic and non-strained cyclic α-oxo oximes, we have now studied 4-(methoxyimino)-2,2,3,3-tetramethylcyclobutanone (1), of which the ring is severely strained, 3,5,5-trimethyl-4(5H)-isoxazolone (8), of which the (Z)-oxime function is constrained in a five membered ring, and 6-(benzyloxyimino)-2,2,5,5-tetramethylcyclohexanone (10), which is a benzyl ether. Upon irradiation of (E)-1 with λ 254 nm, the main process is photodissociation, leading to the same type of products as obtained with the six-membered ring homologue 3, but in a ddition to 2,2,3,3-tetramethyl-4-oxobutanenitrile (13) and 2,2,3,3-tetramethylcyclopropanone O-methyloxime (21).The triplet-sensitized irradiation of (E)-1, in contrast to that of the higher homologues, leads, in addition to E-Z isomerization, to photodissociation, yielding the same photoproducts as obtained after direct irradiation with 254 nm. The isoxazolone 8 is photostable against radiation of 350 and 300 nm.Irradiation of 8 with λ 254 nm leads to population of the excited singlet ??* state and subsequent photodecomposition as a result of initial N-O homolysis, the observed products being carbon monoxide, acetonitrile, acetone and small amounts of ethanol.The occurrence of the photodecomposition is in agreement with the theoretical prediction that the excited singlet ??* (Z)-α-oxo oxime ethers would give N-O homolysis, provided that the other route of deactivation via Z-E isomerization, which has a much lower energy barrier on the potential energy surface, cannot take place. The photochemistry of the benzyl ether (Z)-10, of which the intercarbonyl-iminyl dihedral angle is approx. 45 deg and the ? systems of the phenyl and the C = N - O moieties are perpendicular to one an other, with λ 350, 300 and 254 nm is different from that of the corresponding methyl ether 3 in two ways.Firstly, on using λ 350 and 300 nm decomposition was observed which is, however, slow relative to the Z-E isomerization and, secondly, the photodecomposition products are of a different nature, since the assigned primary and secondary products from 10 are benzaldehyde and 6-(benzoylamino)-2,2,5,5-tetramethylcyclohexanone (32), respectively. Mechanisms have been presented to explain the formation of the photoproducts obtained from 1, 8 and 10.
