Photosensitized regeneration of carbonyl compounds from oximes

Organic Letters

Volumn 4, Issue 14, 2002, Pages 2325-2328

  De Lijser, H J Peter ^a   Fardoun, Fadia H ^a   Sawyer, Jody R ^a   Quant, Michelle ^a  

^a CALIFORNIA STATE UNIVERSITY   (United States)

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ARTICLE;

EID: 0042308849     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol025978a     Document Type: Article

References (29)

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12. In a typical experiment, a solution (5 mL) of the oxime (25 mM) and chloranil (CA; 50 mM) in acetonitrile was photolyzed at 350 nm through Pyrex using a Rayonet reactor (16 lamps) for a maximum of 8 h. The progress of the reaction was followed by capillary column gas chromatography with flame ionization detector (GC/FID) or with mass selective detector (GC/MS). The products were identified by means of their mass spectra and by comparison of the retention times with authentic standards on two different columns. The yields were determined by calibrated GC/ FID.
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25. The proposed first step also implies an important role for the sensitizer as it acts as the base to generate the iminoxyl radical. Preliminary studies on the effect of the photosensitizer on the PET reactions of oximes indicate that photolysis of a solution containing 10 and 1,2,4,5-tetracyanobenzene (TCB) using biphenyl as the co-donor resulted in a low conversion and yield, despite the favorable energetics. This is attributed to the fact that TCB is expected to react via its singlet state and as a result back-electron transfer will be faster than for triplet sensitizers and will lower the yield of the reaction. Furthermore, in the absence of a good base (such as a quinone radical anion), the deprotonation step is slow leading to lower yields.
26. Several mechanisms can be proposed; however, on the basis of these and other experiments, we believe that the two mechanisms discussed here are among the more viable.
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29. Further studies on different oximes indicate that there is a more important role for oxygen than is obvious from these earlier experiments. We will report on these and other mechanistic studies in a future publication.