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Photolysis of nitrites Barton reaction

The further transformation of hydroxy oximes to the nitrone has been observed with llj5-hydroxy-l 8-oximes after thermal treatment or by [Pg.254]

19-Oximino steroids have been prepared starting from 2 -nitrites  [Pg.254]

The yield of 18-oximino compounds from 20jS-nitrites varies from 15 to 36% whereas with a 20oc-nitrite a 60-65% yield is reported. This difference has been ascribed to steric hindrance in the transition state for hydrogen abstraction in the case of the 20j3 derivative. Similar differences [Pg.254]

The nitrites aie most conveniently prepared from the corresponding alcohols by treatment with nitrosyl chloride in pyridine. The crude nitrites can be precipitated by addition of water and recrystallized from appropriate solvents. However nitrites prepared from carbinols in which the adjacent carbon is substituted by halogen, free or esterified hydroxyl or a carbonyl function are very readily hydrolyzed and must be recrystallized with great care. In general the photolysis gives higher yields if purified and dried nitrites are used which do not contain acids or pyridine, although occasionally the addition of small amounts of pyridine is recommended in order to prevent hydrolysis of the nitrite. Traces of acids do in fact catalyze the thermal decomposition of secondary nitrites to equimolar amounts of alcohol and ketone.  [Pg.255]

The irradiations are in general performed under purified, oxygen-free nitrogen in a cylindrical irradiation apparatus with a water-cooled central sleeve into which the lamp is introduced and efficient cooling is used to keep the temperature between 10° and 0° C. Temperatures in the range of 0° to 80° do not influence the photolysis step as demonstrated in the case of a 6j -nitrite, but increase the rate of rearrangement of the nitroso derivative to the oxime. [Pg.255]


II. Functionalization of the Angular Methyl Groups / 237 General principles of substitution / 237 Lead tetraacetate oxidations / 240 Hypohalite reactions / 246 Photolysis of nitrites (Barton reaction) / 253 A-Chloroamine reactions (Hoffmann-Lofller reaction) / 257 Ketone irradiations / 260 Summary / 264... [Pg.244]


See other pages where Photolysis of nitrites Barton reaction is mentioned: [Pg.253]    [Pg.374]   


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