Chromium trioxide reaction with alkenes

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

The reaction of steroid alkenes with sodium azide and chromium trioxide afforded tram-azi-dohydrins, often accompanied by a-oxo azides. A mechanism in which chromyl azide is involved is probably operating. Complete regioselectivity as well as simple and induced diastereoselectivity are generally observed, as determined by II-NMR analysis9. 

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