Subject allylic oxidation

Allyl groups are subject to oxidative deprotection with Chromiapillared Montmorillonite Clay, -BuOOH, CH2CI2, isooctane, 85% yield. Allylamines are cleaved in 84—90% yield, and allyl phenyl ethers are cleaved in 80% yield. 

It has been shown recently that the 1 1 complexes between Hg(II) and a number of olefins are themselves subject to allylic oxidation by Hg(Il) at 80 °C. Typical stoichiometry is... 

Tropones are obtained in good over-all yields when the dihalocarbene adducts of A2- and A3-norcarenes are first allylically oxidized and the resulting ketones subsequently subjected to a dehydrohalogenation sequence [136]. 

The oxidation of propene to acrolein has received much attention for several reasons. Firstly, the process is of industrial importance in itself, and it is also a suitable model reaction for the even more important, but at the same time more complicated, ammoxidation. Secondly, propene oxidation is, in many aspects, representative of that of a class of olefins which possesses allylic methyl groups. Last, but not least, the allylic oxidation is a very successful example of selective catalysis, for which several effective metal oxide systems have been discovered. The subject has therefore attracted much interest from the fundamental point of view. 

Selenium dioxide, Se02, is a widely used reagent for the allylic oxidation of alkenes and ketones. The subject has been extensively covered by recent review articles56,291 293 and only a short summary will be given in this chapter. 

Reissig showed that when a variety of 3-alkoxy-2,5-dihydrofurans were subjected to manganese(lll)-catalyzed allylic oxidation, /3-alkoxylbutenolides were obtained as can be seen in Equation (184). The total synthesis of ( )-annularin H was achieved employing this procedure as a pivotal step <2007SL1294>. 

Attempts have been made to exploit the possibility of direct allylic oxidation of codeine with chromic acid,(253) Mn02,(254) and SeOz plus t-butyl hydroperoxide(255) to the corresponding 14-OH derivative, but each approach gave a low yield. Schwartz and Wallace 255 achieved a six-step transformation of codeine to a noroxycodone (52%) and noroxymorphone (43%) according to Scheme 2.20. Oxidation of the carbamate of norcodeine gave 166 (R = H), which was converted to the dienol acetate, 167. Subjection of this to... 

The first total syntesis of cristatic acid, a potent antibiotic against Gram-positive bacteria, was reported by A. Furstner et al." " The prenylated aromatic substrate (trisubstituted gem-dimethyl alkene) was subjected to a Se02-catalyzed allylic oxidation to obtain stereospecifically the ( )-allylic alcohol. 

The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction which occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds and the adjacent allylic functions are the sites of this chemical activity. Oil oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (18 3) with three double bonds is more susceptible to oxidation than linoleic (18 2) with only two double bonds, which is ten or more times as susceptible as oleic (18 1) with only one double bond. Oxidative deterioration results in the formation of hydroperoxides, which decompose into carbonyls, and dimerized and polymerized gums. It is accelerated by a rise in temperature, oxygen pressure, prior oxidation, metal ions, lipoxygenases, hematin compounds, loss of natural antioxidant, absence of metal deactivators, time and ultraviolet or visible light. Extensive oxidation will eventually destroy the beneficial components contained in many fats and oils, such as the carotenoids (vitamin A), the essential fatty acids (linoleic and linolenic), and the tocopherols (vitamin E). 

Olefins are subject to oxidation both at the double bond and at the allylic position. The CrOs-pyridine reagent in methylene chloride appears to be the most satisfactory reagent for allylic oxidation among the Cr(VI) reagents.Several pieces of mechanistic information indicate that allylic radicals or cations are intermediates in these oxidations. Thus, in cyclohexene is distributed in the product cyclohexenone in a manner indicating that a symmetrical allylic intermediate is... 

N-6-Demethylated ergolines were first allylated, then oxidised to 6-allyl oxides which were subjected to rearrangement to N-6-allyloxy derivatives—Figure 8 (Nordmann and Gull, 1986). Nordmann and Loosli (1985) prepared N-6-carboxamidines from 6-cyano-6-norergolines. 

Linoleic and linolenic acids in fruits and vegetables are subjected to oxidative degradation by lipoxygenase alone or in combination with a hydroperoxide lyase, as outlined in sections 3.7.2.2 and 3.7.2.3. The oxidative cleavage yields oxo acids, aldehydes and allyl alcohols. Among the aldehydes formed, hexanal, (E)-2-hexenal, (Z)-3-hexenal and/or (E)-2-nonenal, (Z)-3-nonenal, (E,Z)-2,6-nonadienal and (Z,Z)-3,6-nonadienal are important for aroma. 

A method for the preparation of amides from aldehydes by oxidation of the corresponding cyanohydrin is described this reaction is subject to the same selectivity as the previously reported method of conversion of aldehydes into esters the aldehyde must be aromatic or ajS-unsaturated to permit allylic oxidation of the cyanohydrin to the a-oxonitiile, which reacts with amines in situ to give the derived amides. 

Both the syntheses in Schemes 11.8 and 11.9 use a two-step oxidation sequence to effect the required oxidation of the allylic methyl group. The first step is a singlet oxygen oxidation to a mixture of hydroperoxides with oxygen bound mainly at carbon atom 2. The mixture is reduced to the corresponding alcohols which were then subjected to oxidation with Cr(VI). The overall yield of this transformation is rather low. 

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