Carbonyl oxides oxygen reactions

Carbonyl oxides (formed by the reaction of diazo compounds with singlet oxygen) may also be used to oxidize sulphoxides74. The corresponding sulphone is formed in reasonable yields and the reaction may be carried out in the presence of the sulphide functionality. The reaction proceeds as shown in equation (21) and involves initial nucleophilic attack by the carbonyl oxide on the sulphoxide sulphur atom followed by the facile departure of the carbonyl compound yielding the required sulphone. 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

The removal of angular methyl groups is important in the transformation of steroids and related compounds. In these reactions, the methyl group is oxidized to the aldehyde before fission in which the carbonyl group oxygen is retained in formate (or acetate), and one oxygen atom from dioxygen... 

The carboxylic acid derivatives li-lm can only be matrix-isolated if the corresponding quinone diazides 2i-2m are irradiated with monochromatic blue light (k = 436 nm).81 91 92 UV or broad-band visible irradiation rapidly results in the decarboxylation of the carbenes. As expected, the IR and UV/vis spectra of the carbenes are very similar to that of la. Oxygen trapping results in the formation of the photolabile carbonyl oxides 7. Thus, the carbenes li-lm were identified both spectroscopically and by their characteristic reaction with molecular oxygen. 

The matrix photochemistry of 2v proved to be fairly complicated.108 The primary product of the photolysis of 2v is carbene lv, which was identified by ESR spectroscopy. Under the conditions of matrix isolation the carbene showed the expected reactivity towards molecular oxygen (formation of carbonyl oxide 7v) and carbon monoxide (formation of ketene lOv) (Scheme 22). In contrast to the oxocyclohexadienylidenes (la and derivatives) carbene lv slowly reacted with CO2 to give an a-lactone with the characteristic C=0 stretching vibration at 1896 cm-1. The latter reaction indicates that lv is — as expected — more nucleophilic than la. 

Some of the earliest studies of triplet carbenes in frozen media by epr spectroscopy revealed that these intermediates react rapidly with molecular oxygen (Trozzolo and Gibbons, 1967). This should not come as a surprise since the combination of a triplet carbene with triplet oxygen is a spin-allowed process. Indeed, recent measurements show that this reaction proceeds with a rate that is approximately at the diffusion limit. The product of this reaction (17) is the expected carbonyl oxide (Werstiuk et al., 1984 ... 

The other advantage of matrix IR spectroscopy is that one can follow the subsequent reaction (either thermally or photochemically) of triplet carbenes relatively precisely, again with the aid of computational methods. " This complementary approach will reinforce the assignment of triplet species. For example, triplet carbenes react with oxygen even at very low temperature to give oxidation products such as carbonyl oxides (see Section 6), which are easUy characterized by comparing the IR spectra with those calculated. 

The synthesis of fenozan BO-7 4 involves two key steps, the first of which employs a 4 + 2 cycloaddition of singlet oxygen to the diene 83a122-20 123. This provides the endoper-oxide 83b that can be transformed into the target cis-fused 1,2,4-trioxane by treatment with the Lewis acid, TMSOTf, in the presence of a carbonyl compound. The reaction proceeds by Lewis acid promoted heterolysis of the C—O bond to give an intermediate peroxy allyl cation 83c that is captured by the carbonyl compound (in this case, cyclopen-tanone) to give the product (Scheme 30). A number of different carbonyls have been used in this reaction along with a number of different endoperoxide templates and detailed SAR have been developed (Scheme 30). 

Chapter 6 (Addition), Chapter 7 (Carbonylation), Chapter 8 (Acylation), and Chapter 10 (Heterosubstitution) deal with derivatization reactions to form carbon-heteroatom bonds. The important broad field of hydrocarbon oxidations is covered in Chapter 9 (Oxidation-oxygenation). Both the chemistry brought about by... 

Attempts to trap carbenes 3b and 3d with molecular oxygen, a reaction frequently used to characterize triplet carbenes, were successful at high (>5%) concentrations of O2 in the argon matrix22. In both cases, the corresponding silyl formate was detected, and it was assumed that a carbonyl oxide and a dioxirane are intermediates in this carbene trapping... 

Photolysis of matrix-isolated (trimethoxysilyl)diazomethane at X > 305 nm produced carbene 3e (equation 1), which was characterized by IR and UV-Vis spectroscopy23. Under these conditions, no other species besides the carbene could be detected spectroscopically. In an 02-doped (1%) argon matrix, the carbene rapidly reacted with oxygen to give carbonyl oxide 4 which was further photoisomerized to formylsilane 5. Again, the fast reaction of 3e with 302 points to a triplet ground state of the carbene. 

The reaction of irans-di-iert-butylethylene (15) with ozone is shown in Scheme 8. The ozonide (16) is an unusually stable (at 60 °C) trioxolane50. The decomposition of (16) forms the aldehyde (17) and the carbonyl oxide (18) (as illustrated in Scheme 8, for non-radical ozonization reactions). The carbonyl oxide is an oxygen carrier. 

The decomposition of (18) in the presence of electron-deficient oxygen acceptors such as tetracyanoethylene forms the tetracyanoethylene oxide (19)51, with 60% yield. The oxygen atom transfer may be considered a general reaction of carbonyl oxides in ozonolysis of C=C double bonds when oxygen-accepting substrates are present. 

One hydroxyl is missing, and a new hydroxyl has been incorporated adjacent to the methyl. Without any evidence for the sequence of such reactions, the structure of intermediate 2 shows the result of three aldol condensations and reduction of a carbonyl. A dehydration reaction, two oxidations, and a decarboxylation are necessary to attain the islandicin structure. In chrysophanol, aloe-emodin, and rhein, the same oxygen function is lost by reduction as in islandicin, and decarboxylation also occurs. The three compounds... 

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