Chromium Oxidations in Organic Chemistry by Professor Gianfranco Cainelli, Professor Giuliana Cardillo

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By Professor Gianfranco Cainelli, Professor Giuliana Cardillo (auth.)

Chromium oxidation, renowned and extensively explored in natural chemistry because the very starting of this technological know-how, is a subject of present curiosity for the natural chemist as evidenced via the continual improvement of recent techni­ ques and approaches pronounced within the literature. Chromium oxidation is a straightforward approach which are simply played within the laboratory and scaled up in to boot. even though nearly each oxidizable natural sensible team could suffer chromium oxidation, an important fields of appli­ cation are the oxidation of alcohols, allylic and benzylic oxidation, oxidative degradation and oxidation of a few organometallic compounds. A excessive measure of selectivity is frequently attainable through deciding on the main appropriate reagent between these numerous ones now to be had. This ebook takes account of some of the practical teams that endure oxidation and the complete literature as much as 1982. it's been written within the wish to aid the artificial natural chemist in his experimental paintings. For this objective a few tables comprising yields and references were integrated; designated descriptions of normal strategies are supposed to express the experimental stipulations and the scope of the reactions. we want to thank Dr. Mario Orena for his helpful medical and technical assistence and Prof. Bruno Camerino, who learn the whole manuscript and corrected some of the error. Bologna, February 1984 Gianfranco Cainelli Giuliana Cardillo desk of Contents I. advent . . . . . . . . . . .

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Oxidation of Carbon-Hydrogen Bonds In L1 5 -cholestenes there are two conformationally rigid sites of allylic hydrogens (C-4 and C-7). It can be expected that axial hydrogens will be preferentially abstracted because of a more favorable stereoelectronic location in the developing p-orbital and n-system. H In this particular case the axial hydrogen on C-4 lies above the plane of the molecule and the approach of the oxidant would be hindered by the angular methyl group. In contrast, the axial hydrogen at C-7 is free from such steric interference being below the plane of the molecule.

59). With an excess of chromyl chloride the bimolecular pathway dominates, leading to a "normal" Etard complex of the type formed by toluene. c. ,{3unsaturated ketones has been widely employed in the synthesis and transformation of natural products. Chromium trioxide or sodium dichromate in acetic anhydride or acetic acid appear to be useful for allylic oxidation especially in steroid chemistry although the yields are sometimes unsatisfactory. Better results have been recently obtained with tert-butyl chromate, chromium trioxide-pyridine complex, and pyridinium chlorochromate in anhydrous aprotic media.

Oxidation of Carbon-Hydrogen Bonds boiling acetic acid affords, in addition to the expected product of allylic oxidation, the y-lactone 3,3-dimethyl-2-oxy-A-norcholest-5-en-1, 7-dione [90]: ~+ 28% 16% Aliphatic and monocyclic compounds generally give poor yields owing to the lack of regioselectivity of the oxidation and concomitant cleavage of the double bond. The oxidatinn of cyclohexene with chromic acid in aqueous acetic acid, for instance, affords cyclohexenone in 37 % yield, and adipic acid as the other principal product at a 25 % yield.

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