Reactivity of Carbonyl Oxides. Characteristic Nucleophilic Oxygen Atom Transfer from R2COO beside Electrophilic and Radical Reactions

Article abstract of DOI:10.1021/ja00403a034

According to a MINDO/3 calculation, carbonyl oxide H2COO has a large contribution of zwitterionic structure 1a, which is not altered by phenyl substituent.The dye-sensitized photooxidation of diazomethanes in CH2Cl2 - MeOH afforded ca. 30percent yield of α-methoxy hydroperoxides as product from 1a and MeOH.Relative reactivities of various types of substrates toward the carbonyl oxide from diazofluorene and ¹O₂ have been determined.While benzene gave phenol in a low yield, substituted benzenes such as toluene or anisole yielded products by hydrogen atom abstraction on the side chain as a major reaction.Olefins gave a rather minor amount of epoxides; the predominant reaction was C-C cleavage or allylic hydrogen abstraction.The realtive reactivity with carbonyl oxide is in the order Ph2SO >> Ph2S > C = C > benzene, where C = C means α-methylstyrene.This order is in sharp contrast to the case of peroxy acid, Ph2S >> Ph2SO >> C = C, or to the order with acylperoxy radical, C = C >> Ph2S, Ph2SO.The above order with carbonyl oxide indicates a nucleophilic oxygen atom transfer as a characteristic reaction; this was clearly shown by the positive ρ value of +0.26 for substituted diphenyl sulfoxides.The reactivities of various substrates revealed that another characteristic reaction is hydrogen atom abstraction as a radical, and carbonyl oxides could be regarded as a rather poor electrophilic O-transfer agent.These features may be understood by representing carbonyl oxides as a resonance hybrid of R2C=O⁺-O^- (1a) and R2C^*-O-O^* (1c).