79984-94-4Relevant academic research and scientific papers
Photochimie organique: photolyse de O-benzoylbenzamides secondaires et tertiaires
Gramain, Jean-Claude,Lhomme, Marie-France
, p. 141 - 146 (2007/10/02)
Intramolecular photoreduction of ketones leads to a diradical likely to undergo cleavage or cyclization to yield cyclobutanols (Norrish type II reaction).Examples of intramolecular δ- or ε-H-abstraction are known to lead to 1,5- or 1,6-diradicals, the cyclization of which gives rise to five or six-membered rings.We have prepared a series of O-benzoyl-benzamides and studied their photolysis in order to establish a pathway to phenyltetrahydroisoqoinolines.We have thus prepared N-ethyl, N-isopropyl and N-benzyl-O-benzoylbenzamides and shown that in solution these compounds have a cyclic structure (3-hydroxy-3-phenylphtalimidine) in which the ketone carbonyl is hidden.These compounds are photochemically inert.Four tertiary O-benzoylbenzamides have been prepared (N,N-diethyl, N,N-di-n-butyl, N-butyl-N-methyl, and N-benzyl-N-methyl).These compounds exhibit an n?* absorption above 300 nm.Their photolysis (λ > 300 nm) gives rise in all four cases to the 3-phenylphtalide 9 and to their dimer 10 of the 3-phenylphtalid-3-yl radical (meso and d,l) mixture.Upon irradiation below 300 nm (253.7 nm in quartz), formation of the diphtalide (dimer 10), not of the phenylphtalide 9, is observed.Finally no cyclic photoproducts derived from a 1,6-diradical are observed.In thus appears that deactivation of the excited state of tertiary O-benzolylbenzamides does not occur by intramolecular abstraction of the hydrogen α to the amide nitrogen atom, but rather by homolytic cleavage of the amide C-N bond.The radical thus formed cyclizes, giving a 3-phenylphtalid-3-yl radical which further yields, either the 3-phenylphtalide 9 by hydrogen capture, or the dimer 10 by coupling.During irradiation at 253.7 nm the optical density of the solution is very high (of the order of 1000) because of the high ε values of the starting compounds.The local concentration of 3-phenylphtalid-3-yl radicals is thus high, promoting their coupling to dimer at the expense of hydrogen capture, which would lead to the 3-phenylphtalide 9.
