Oxygen shifts

The isomerisation of allyl and propargylic alcohols involves the 1,3-shift of an oxygen atom rather than a hydrogen atom. Isomerisation of allyl alcohols can be catalysed by a variety of metal oxo complexes and in this instance the reaction does not involve metal carbon bonds as we will see. One could imagine that allylic metal species can participate in isomerisation of allylic compounds, but for the alcohols themselves this is not an easy reaction. In chapter 13 reactions of allyl acetates and the like, which are more prone to 

3 Akutagawa, S. Chapter 16 in Chirality in Industry, Ed. Collins, A. N. Sheldrake, G. N. Crosby, J. 1992, Wiley. 

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Interestingly, the oxygen-17 chemical shifts for the thiirane oxide (16a) and thiirane dioxide (17a) were found to be 71 and 111 ppm (downfield from natural-abundance 170 in HzO), respectively. The oxygen-17 shift reveals that this oxygen is the most highly shielded oxygen atom so far reported80,70. 

The first systematic study of chemical shifts in lanthanide complexes involved measurement and interpretation of oxygen-17 shifts of aquo complexes and the sign variation of the observed shifts in the series. The 170 shifts of Dy3+ and Ho3+ perchlorates conform to the Curie law of equation (10.8) and the corrections due to second order treatment for the ions are small [16]. 

Fig. 10.4. The water oxygen-17 shift in 1 molal R(C104>3 solutions plotted against (Sz)-...

SD and 8 0 values for epithermal deposits from other countries are summarized in Fig. 1.105 (Field and Fifarek, 1985). The oxygen shift away from the meteoric water line is always observed, but 8D is similar to meteoric water value, suggesting meteoric water source of epithermal ore fluids. Magmatic contribution to ore fluids has not been found except in some ore fluids responsible for the deposits in the other countries Tui... 

The domino reaction is initiated by the chemoselective attack of the carbanion 2-458 on the terminal ring carbon atom of epoxyhomoallyl tosylate 2-459 to give the alkoxides 2-460 after a 1,4-carbon-oxygen shift of the silyl group. The final step to give the cyclopentane derivates 2-461 is a nucleophilic substitution. In some cases, using the TBS group and primary tosylates, oxetanes are formed as byproducts. 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Lenard, J., and G. P. Hess An approach to the specific cleavage of peptide bonds. II. Specific cleavage of peptide chains based on the hydrogen fluoride induced nitrogen to oxygen. shift. Journ. Biol. Chem. 239, 3275 -3281 (1964). 

The scheme shows that non-rearranged allylic alcohols are formed via a [1,2] tellurium-oxygen shift followed by hydrolysis. 

It may be stated at this point that the presence of a /3-hydroxy-butyrate fat in certain organisms is a matter of general biochemical importance. Usually /3-hydroxybutyric acid and the acetone bodies are derived from n-butyric acid directly. The unambiguous formation of jS-hydroxybutyric acid anhydrides from carbohydrates opens up new vistas its formation from acetaldehyde, and from pyruvic acid, through aldol intermediates can be understood without difficulty. Kirrmann s reaction, to which little attention has been paid, is at the same time an example of an oxygen shift, leading from hydroxyaldehydes to fatty acids. 

Two types of catalysts, Rh/SiO and Rh-CeO /SiO, were used. The reactivity tests (185°C, 1 atm.) showed that the presence of cerium affected the activity and also the selectivity of Rh/SiO catalysts. The total conversion (calculated as mole per cent of CO converted) after 8 hours on stream was 3.8% on Rh/SiO and 1.9% on the cerium containing catalyst. What is most striking is that the selectivity to oxygenates shifted from 6 to 71% by the addition of cerium. On Rh/SiO, acetaldehyde was obtained as the major oxygenated product whereas on Rh-CeO /SiO catalysts ethanol was the most abundant product. 

The thermal decomposition of ascaridole (166) in xylene results in an oxygen shift to form 193.240-244 rpyg jSOmerization is thought to proceed via the diepoxide (192). A similar isomerization occurs in the thermal decomposition of some steroid peroxides 194 is formed in 15 % yield when ergosterol peroxide is heated in vacuo at 220°.246... 

Electronegative elements like halogen, nitrogen, and oxygen shift absorptions downfield. 

Diazo compounds 502 generated by the reaction of chlorophosphines with silver diazo compounds undergo spontaneous decomposition into A" -1,3-diphosphetes 504. Formation of the latter can be rationalized by the intermediacy of A o -phosphaalkynes 503 followed by dimerization and a P- P oxygen shift [85ZN(B)1258 86TL1903]. 

The migration of oxygen from a quaternary center in a cyclohexadienone may be preferred to a carbon shift, when present as an ether or ester function rather than free hydroxy. Thus the p-quinol acetate (117) yields the orcinol monoacetate (118 79%) on treatment at room temperature with trifluoroacetic anhydride, and the p-quinol ether (119) forms the resorcinol diethyl ether (120 71%) in ethanolic sulfuric acid. In the second case, hemiketalization must intervene also some methyl shift (12%) is observed. With the quinol (121), treatment with acetic anhydride-sulfuric acid leads to the lactone (122) acetylation or lactonization probably precedes oxygen shift. A number of related examples can be found in the steroid area. - Thermal 1,3-shifts of p-quinol acetates can also be induced acetate (117) yields catechol acetate (123 50-60%, 45 °C) by way of isomerization of the first-formed acetate (124). In the o-quinol acetate series, 1,2-acetoxy shift is seen in (125) (126 92%) and in (127) (128 90%), both in... 

The thermal isomerization of arylamine A-oxides 189 into substituted hydroxylamines 190 is known as the Meisenheimer rearrangement (see review in Reference 278, and Reference 279) (equation 74). In this case279 the Meisenheimer rearrangement (i.e. the [2,3]-sigmatropic shift 189 —> 190) is followed by [1,3] oxygen shift to carbon (190 — 191) on further heating. 

Strain-rate dependence of ductility of the form shown in Fig. 7.81 is presented in Fig. 7.82 for a carbon steel in a carbonate-bicarbonate environment (Ref 119). The ductility is represented as the ratio of the reduction in area (RA) in the environment relative to the value in inert oil. The tests were conducted at the indicated constant potentials and illustrate that the strain-rate dependence can be sensitive to the potential, particularly the minimum ductility and the strain rate at which the minimum occurs. It follows, as an illustration, that if small changes in the environment, such as dissolved oxygen, shift the potential from -720 to -680 mV (SHE), significant changes in susceptibility to SCC would be predicted. 

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