Photooxygenations of sydnones and azomethine imines

Abstract

Sensitized photooxygenations of a few sydnones and azomethine imines have been studied. The photooxygenation of 3,4-diphenylsydnone (lb), for example, gave a 25% yield of a,d-dibenzoylphenylhydrazine (16b) as the only isolable product, whereas the photooxygenation of 4-phenyl-3-p-tolylsydnone (lc) resulted in the formation of a mixture of products containing ,/3-dibenzoyl-p-tolylhydrazine (16c, 8%) and 4,5-diphenyl-2-p-tolyl-1,2,3-triazole (8c, 8%). Under analogous conditions, 3-phenyl-4-p-tolylsydnone (Id) gave a mixture of products consisting of , -di-p-toluylphenylhydrazine (16d, 10%) and 2-phenyl-4,5-di-p-tolyl-l,2,3-triazole (8d, 1%). Irradiation of Id in either benzene or methanol and in the absence of any oxygen gave the triazole 8d as the only isolable product. Similarly, the photooxygenation of 3-methyl-4-phenylsydnone (le) in methanol gave a mixture of benzoic acid (12b, 10%) and ,ß-dibenzoylmethylhydrazine (16e, 5%), whereas irradiation of le in benzene gave a 10% yield of 4-methyl-2-phenyl-A2-l,3,4-oxadiazolin-5-one (5e). The photooxygenation of an azomethine imine, namely, C-biphenylene-7Va-(4-chlorophenyl)-iV8-cyanoazomethine imine (19), gave a 78% yield of 9-fluorenone (21). Reasonable mechanisms have been suggested for the formation of the various products in these reactions.

Oxadiazoles

“…In the presence of Rose Bengal as a sensitizer, singlet oxygen adds to a sydnone as a dipolarophile. The identification of benzoic acid and dibenzoylphenylhydrazine among the reaction products has been rationalized on the basis of two simultaneous reaction pathways (Scheme 13.25) [77]. Several sydnones develop a color when irradiated by UV light; for instance, a blue color has been observed by irradiation of the 3-(3-pyridyl)sydnone.…”

Increasing the index of covalent oxygen bonding at nitrogen attached to carbon

“…Thermolysis of 3-azidopyridazine 2-oxide (151) in refluxing toluene gave (3-cyanoacrolein (153) and 1-hydroxy-5-cyanopyrazole (154; eq 1 18, 119).138-139 in a similar manner azide 151 (R = OCH3) gave c/s-^-cyanoacrylate but azide 151 (R = Cl, gave maleonitrile, apparently by an elimination of nitrosyl The contraction of a nitrosimine (152) into a carbonyl compound (153) is an example of a recently developed reaction.140 Each of nine nitroso ketimines 156, from an imine (155) and nitrosyl chloride at -10 °C (eq 120) readily fragmented into a RR'C=NH 7^-RR C=NN0 " RR C=N=N0 --- 155 156 157 analogy with nitrosamines, R2NNO R2N+=NO", supported contributions from 1,3-and 1,4-zwitterionic structures 157 and 158.…”

“…Stable adducts with increased nitrogen-oxygen bonding are unknown for 1,3-dipoles; a nitrile imine, diazoalkane, azide, nitrous oxide, azomethine imine, azimine, azoxy compound, carbonyl imine, and nitrosimine.73,95 An inability for N,C-diphenylnitrilimine (C8H5C+=NN"C8H5) to give a sensitized reaction with singlet oxygen was recently observed. 153 A formation of benzoic acid was accounted for by invoking a sensitized 1,3-dipolar photooxygenation of 3,4-diphenylsydnone followed by an elimination of carbon dioxide, rearrangement of A/-nitrosobenzanilide (section IV.A) and hydrolysis of a diazotate ester (eq 141);153 however, an alternative route…”

Photooxygenations of nitrogen heterocycles

“…Sensitized photooxygenations of a few bicyclic aziridines have been studied recently. 15 The photooxygenation of 1-cyclohexyl-6-(cyclohexylimino-)-1a-phenylindano[1,2-d]aziridine (9) is reported to give a 51% yield of 2-cyclohexyl-3-hydroxy-3phenylphthallmidine (14), and the formation of this product has been rationalized in terms of the intermediates 10,11,12, and 13 as shown in Scheme II. It is pertinent to observe that Padwa and Vega16 had suggested earlier that the photolysis of 9 in presence of oxygen gives rise to a 10% yield of 13. It is likely that singlet oxygen is generated in this system through the reaction of the triplet state of either 9 or 10 with ground-state (triplet) oxygen.…”