- Reduction of organic halides with lanthanum metal: A novel generation method of alkyl radicals
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Results of the reaction of alkyl halides with lanthanum metal have been shown. The reduction of alkyl iodide with 1/3 equiv of lanthanum metal efficiently proceeded to give the corresponding reductive dimerized products along with the formation of reduction and dehydroiodination products. In the case of alkyl bromides and chlorides, the reaction did not proceed under the same reaction conditions as that of alkyl iodides; however, the reaction was dramatically promoted by the addition of a catalytic amount of iodine. A reaction pathway including alkyl radicals was suggested.
- Nishino, Toshiki,Watanabe, Toshihisa,Okada, Mitsuo,Nishiyama, Yutaka,Sonoda, Noboru
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p. 966 - 969
(2007/10/03)
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- Exploitation of aldoxime esters as radical precursors in preparative and EPR spectroscopic roles
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Photolyses of aldoxime esters, containing a considerable range of alkyl groups, lead to cleavage of their N-O bonds and formation of aryliminyl and alkyl radicals. The process was found to be favoured by 4-methoxyacetophenone as a photosensitiser and by methoxy substituents in the aryl rings. 4-Nitro- and pentafluoro-substitutions of the aryl rings were, on the other hand, deleterious. The intermediate iminyl radicals, together with primary, secondary and tertiary alkyl radicals were characterised by 9 GHz EPR spectroscopy. Cyclopropyl, CF3, and CCl3 radicals were probably also formed, but were too reactive for direct EPR spectroscopic detection. Photosensitised reaction of benzophenone oxime O-nonanoyl ester produced the diphenylmethaniminoxyl, as well as the expected n-octyl and iminyl radicals. This indicated that O-C bond scission accompanied O-N scission for this ketoxime ester. At higher temperatures the C-centred radicals added to the starting oxime esters to produce alkoxyaminyl radicals that were also spectroscopically detected in some cases. No evidence for abstraction of the iminyl hydrogen by tertbutoxyl radicals was obtained. Instead, the t-BuO radicals added to the C=N double bonds of the oxime esters. Similarly, chlorine abstraction from alkylbenzohydroximoyl chlorides by trimethyltin radicals did not take place. Preparative scale experiments with oxime esters containing suitably unsaturated alkyl groups showed that good yields of cyclised products could be obtained in the presence of the photosensitiser. This process constitutes a general method by which carboxylic acids or acid chlorides can be converted into alkyl radicals and hence to cyclised derivatives.
- McCarroll, Andrew J.,Walton, John C.
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p. 2399 - 2409
(2007/10/03)
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- Enhanced radical delivery from aldoxime esters for EPR and ring closure applications
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Arylmethaniminyl and alkyl radicals were generated from di- and tri- methoxyphenyl aldoxime esters, by photolysis in the presence of 4- methoxyacetophenone, and were detected by EPR spectroscopy: good yields of cyclised products were isolated from suitably unsaturated alkyl substituents.
- McCarroll, Andrew J.,Walton, John C.
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p. 351 - 352
(2007/10/03)
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