Oxidation stereospecific

PerfluoroaUcenes are converted to vicinal diols when no fluonne atom is present at the double bond Configurational isomers of perfluoroalkenes [29] (equations 20 and 21) are oxidized stereospecifically Perfluorbicyclo[4 3 0]non-1(6) ene gives the corresponding 1,6 diol m a 24% yield upon oxidation with potassium permanganate at 18 °C for 1 h [29]... 

Bis(trimethylsilyl)peroxide (1) can be used to produce phosphine oxides stereospecifically from either phosphines (with retention) or phosphine sulphides (with inversion).1 A variety of organoelement substituted pentadienes, including the phosphine oxides (2) and (3),... 

Several microbial alcohol oxidoreductases can catalyze the stereoselective oxidation of GLD. Quinohaemoprotein ethanol dehydrogenase of Acetobacter pasteurianus is able to oxidize stereospecifically (S)-GLD to (l )-glycidic acid in racemic GLD [41,42 ]. When washed cells of A. pasteurianus were incubated with 4.8 mg ml" of racemic GLD, (1 )-GLD was obtained, with an optical purity of 99.5% e. e. and 64% conversion. 

The reaction of cyclohexene with Mn (111 )(sal en )/t -B uOOH afforded cyclohexene oxide as the single product in the presence of radical inhibitors. When PhIO was used as the terminal oxidant, stereospecific epoxidation could be attained. Similar results were obtained with Co(II)(salen) (5) stereospecific epoxidation took place with PhIO as the... 

A related oxidative rearrangement of cephem dioxides has been reported in which an alkene is oxidized stereospecifically with rearrangement to the allylic alcohol in good yield by simple exposure to a palladium/caibon catalyst, as depicted in equation (12). Adventitious oxygen preadsotbed on the catalyst seems the likely oxida The reaction fails on the parent ccphem or its monoxide, or on the free acid of the dioxide. This reaction would seem to hold some promise for furdier utility in the cephem field and odier related systems. 

Olefins can be oxidized stereospecifically to cz,y-a>glycols by aqueous potassium chlorate solutions118 or, better, silver chlorate solutions119 if a little osmium tetroxide is added (Hofmann). The method is suitable mainly for conversion of water-soluble olefins into glycols and cannot be used for water-insoluble olefins.120,121... 

Watanabe, A., Uchida, T., Irie, R., et al. (2004). Zr[bis(salicylidene)ethylenediaminato]-Mediated Baeyer-Villiger Oxidation stereospecific Synthesis of Abnormal and Normal Lactones, Proc. Natl. Acad. Sci. USA, 101, pp. 5737-5742 Watanabe, A., Uchida, T., Ito, K.,... 

The Coleoptera (beetles) contains about 300,000 species and are very varied in form, diet and habitat. Equally they have very different kinds of pheromones and defensive secretions, many of them derived from fatty acids. The bean weevil Acanthoscelides obtectus uses an unusual allenic methyl ester (Figure 3.25). Its biosynthesis has not yet been investigated. Allenes are an unusual example of chirality. Anomala cuprea, a chafer grub produces two lactone sex attractants, derived from the unsaturated acids oleic and palmitoleic acids (Figure 3.25). Both are shortened by the loss of two acetic acid units, then oxidized (stereospecifically) at the allylic position and cyclized to the pheromone. 

Watanabe A, Uchida T, Irie R, Katsuki T. Zr[bis(salicylidene) ethylenediaminato]-mediated Baeyer-Villiger oxidation stereospecific synthesis of abnormal and normal lactones. Proc. Natl. Acad. Sci. USA 2004 101 5737-5742. 

Electron-deficient alkenes add stereospecifically to 4-hydroxy-THISs with formation of endo-cycloadducts. Only with methylvinyl-ketone considerable amounts of the exo isomer are produced (Scheme 8) (16). The adducts (6) may extrude hydrogen sulfide on heating with methoxide producing 2-pyridones. The base is unnecessary with fumaronitrile adducts. The alternative elimination of isocyanate Or sulfur may be controlled using 7 as the dipolarenOphile. The cycloaddition produces two products, 8a (R = H, R = COOMe) and 8b (R = COOMe, R =H) (Scheme 9) (17). Pyrolysis of 8b leads to extrusion of furan and isocyanate to give a thiophene. The alternative S-elimi-nation can be effected by oxidation of the adduct and subsequent pyrolysis. 

Overall the stereospecificity of this method is the same as that observed m per oxy acid oxidation of alkenes Substituents that are cis to each other m the alkene remain CIS m the epoxide This is because formation of the bromohydrm involves anti addition and the ensuing intramolecular nucleophilic substitution reaction takes place with mver Sion of configuration at the carbon that bears the halide leaving group... 

Deamination, Transamination. Two kiads of deamination that have been observed are hydrolytic, eg, the conversion of L-tyrosiae to 4-hydroxyphenyUactic acid ia 90% yield (86), and oxidative (12,87,88), eg, isoguanine to xanthine and formycia A to formycia B. Transaminases have been developed as biocatalysts for the synthetic production of chiral amines and the resolution of racemic amines (89). The reaction possibiUties are illustrated for the stereospecific synthesis of (T)-a-phenylethylamine [98-84-0] (ee of 99%) (40) from (41) by an (5)-aminotransferase or by the resolution of the racemic amine (42) by an (R)-aminotransferase. 

In a first step, JS ocardia asteroides selectively oxidizes only (3)-pantolactone to ketopantolactone (19), whereas the (R)-pantolactone remains unaffected (47). The accumulated ketopantolactone is stereospecificaHy reduced to (R)-pantolactone in a second step with Candidaparapsilosis (product concentration 72 g/L, 90% molar yield and 100% ee) (48). Racemic pantolactone can also be converted to (R)-pantolactone by one single microbe, ie, Jiodococcus erythropolis by enantioselective oxidation to (3)-pantolactone and subsequent stereospecific reduction in 90% yield and 94% ee (product concentration 18 g/L) (40). 

Ring contraction of 2-thiocephems has also been examined as a route to penems. Desulfurization of (82, n = 0) using triphenylphosphine gave mixtures of 5(R)- and 5(5)-penems (121). The stereochemical problem was neatiy overcome by regioselective oxidation to the thiosulfonate (82, n = 2) which underwent stereospecific thermal extmsion of sulfur dioxide (122) to give the S(R)-penem (83). 

N- Aminoaziridines have been converted to alkenes by reaction with a variety of oxidizing agents (70JA1784). Usually, the deamination reaction is stereospecific. The oxidation of l-amino-2,3-diphenylaziridines with manganese dioxide, however, was not stereospecific. The trans compound gives entirely frans-stilbene, whereas the cfs-aziridine forms a mixture of 85% trans- and 15% c -aikene. cw-Stilbene is not isomerized to trans under the reaction conditions, and the results are explained in terms of an azamine intermediate which can isomerize through a tautomeric equilibrium. 

Alkylaziridines can be stereospecifically deaminated to alkenes by reaction with m-chioroperbenzoic acid (70AG(E)374). The reaction and work-up are carried out in the dark to avoid isomerization of the cw-alkene, and the mechanism is thought to involve an initial oxidation to an amine oxide followed by a concerted elimination. Aziridine oxides have been generated by treating aziridines with ozone at low temperatures (71JA4082). Two... 

Other non-oxidative procedures have also been used to deaminate aziridines. For example, aziridines react with carbenes to yield ylides which subsequently decompose to the alkene. Dichlorocarbene and ethoxycarbonylcarbene have served as the divalent carbon source. The former gives dichioroisocyanides, e.g. (281), as by-products (72TL3827) and the latter yields imines (72TL4659). This procedure has also been applied to aziridines unsubstituted on the nitrogen atom although the decomposition step, in this case, is not totally stereospecific (72TL3827). 

Electron deficient carbon-carbon double bonds are resistant to attack by the electrophilic reagents of Section 5.05.4.2.2(t), and are usually converted to oxiranes by nucleophilic oxidants. The most widely used of these is the hydroperoxide ion (Scheme 79). Since epoxidation by hydroperoxide ion proceeds through an intermediate ct-carbonyl anion, the reaction of acyclic alkenes is not necessarily stereospecific (Scheme 80) (unlike the case of epoxidation with electrophilic agents (Section 5.05.4.2.2(f)) the stereochemical aspects of this and other epoxidations are reviewed at length in (B-73MI50500)). 

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