889665-09-2Relevant articles and documents
Photochemical cleavage and release of para-substituted phenols from α-keto amides
Ma, Chicheng,Chen, Yugang,Steinmetz, Mark G.
, p. 4206 - 4215 (2007/10/03)
In aqueous media α-keto amides 4-YC6H4OCH 2COCON(R)CH(R′)CH3 (5a, R = Et, R′ = H; 5b, R = iPr, R′ = Me) with para-substituted phenolic substituents (Y = CN, CF3, H) undergo photocleavage and release of 4-YC 6H4OH with formation of 5-methyleneoxazolidin-4-ones 7a,b. For both 5a,b quantum yields range from 0.2 to 0.3. The proposed mechanism involves transfer of hydrogen from an N-alkyl group to the keto oxygen to produce zwitterionic intermediates 8a-c that eliminate the para-substituted phenolate leaving groups. The resultant imminium ions H2C=C(OH) CON+(R)=C(R′)CH3 9a,b cyclize intramolecularly to give 7a,b. The quantum yields for photoelimination decrease in CH3CN, CH2Cl2, or C6H6 due to competing cyclization of 5a,b to give oxazolidin-4-one products which retain the leaving group 4-YC6H4O- (Y = H, CN). A greater tendency to undergo cyclization in nonaqueous media is observed for the N,N-diethyl amides 5a than the N,N-diisopropyl amides 5b. With para electron releasing groups Y = CH3 and OCH3 quantum yields for photoelimination significantly decrease and 1,3-photorearrangment of the phenolic group is observed. The 1,3-rearrangement involves excited state ArO-C bond homolysis to give para-substituted phenoxyl radicals, which can be observed directly in laser flash photolysis experiments.
