Ozonization stereospecific

A technique based on ozonation, in contrast, provides information on the stmcture of the lignin side chain by degrading the aromatic rings (33). Thus the side chain of the dominant stmcture ia all native lignins, the arylglycerol—P-aryl ether moiety, can be obtained ia the form of erythronic and threonic acids. Ozonation proves to be an elegant method for determination of the stereospecificity ia lignin. 

Ozonation ofAlkenes. The most common ozone reaction involves the cleavage of olefinic carbon—carbon double bonds. Electrophilic attack by ozone on carbon—carbon double bonds is concerted and stereospecific (54). The modified three-step Criegee mechanism involves a 1,3-dipolar cycloaddition of ozone to an olefinic double bond via a transitory TT-complex (3) to form an initial unstable ozonide, a 1,2,3-trioxolane or molozonide (4), where R is hydrogen or alkyl. The molozonide rearranges via a 1,3-cycloreversion to a carbonyl fragment (5) and a peroxidic dipolar ion or zwitterion (6). 

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... 

An interesting feature of the synthesis is the use of allyl as a two-carbon extension unit. This has been used in the stereospecific synthesis of dicyclohexano-18-crown-6 (see Eq. 3.13) and by Cram for formation of an aldehyde unit (see Eq. 3.55). In the present case, mannitol bis-acetonide was converted into its allyl ether which was ozonized (reductive workup) to afford the bis-ethyleneoxy derivative. The latter two groups were tosylated and the derivative was allowed to react with its precursor to afford the chiral crown. The entire process is shown below in Eq. (3.59). 

In the refined Criegee mechanism615,616 that includes orbital symmetry considerations as well,617 all three steps are stereospecific. Ozonation of cis- and trans-[1,2-2H2] ethylene, for instance, gave the exo and endo isomers according to Eqs. (9.110) and (9.111) (the cis-exo and cis-endo ozonides from the cis compound, and the trans ozonide form the trans isomer) 602... 

Additional evidence for the stereospecific conversion of fi-O-4 and arylglycerol lignin models to tetronic acids under conditions that selectively oxidize aryl rings also comes from acidic permanganate oxidation (Tsutsumi et al. 1990). This method gives essentially the same products as ozonation. 

The contribution of Ic is not considered likely the possible rotation about the carbon-carbon <7 bond would result in a non-stereospecific ozone addition on the olefin—in violation of Greenwood s observations (21,22) that a trans- (or cis-) olefin yields only trans- (or cis-) primary ozonide. Retention of configuration is also shown in those cases in which epoxide is formed (20). Finally, a recent communication by Bailey et al. (23) reports the formation of free radicals, arising from the homolytic dissociation of a w or a complex, in the ozonolysis of terminal olefins with bulky substituents capable of stabilizing free radicals. 

Derivatives of phosphonic acids, RP==O(0H)2, can be prepared by several different oxidative methods. Primary phosphines RPH2 are oxidized to phosphonic acids by hydrogen peroxide or by sulfur dioxide thus, phenylphosphine gave benzenephosphonic acid (96%) on reaction with sulfur dioxide at room temperature in a sealed tube. Phosphinic acids, RI sO(OH)H, can also be oxidized to the corresponding phosphonic acids with hydrogen peroxide. Ozone oxidized the dioxaphosphorane (54) to the phosphonic ester in 73% yield. Ozone is also capable of stereospecific oxidation of phosphite esters to phosphates. For example, the cyclic phosphite (SS) was oxidized to the phosphate (56) with retention of configuration. Peroxy acids and selenium dioxide are other common oxidants for phosphite esters. 

The oxidation of sulfides to sulfoxides is a facile transformation for which many reagents have been employed in the literature. These include hydrogen peroxide, ozone, nitric acid, chromic acid or tert-butylhypochlorite. Here, meto-chloroperbenzoic acid is used to oxidize a-phenylthio ketone 14, and successive elimination of the resulting a-phenylsulfinyl ketone 15 by heating at reflux in benzene provides the or,ji3-unsaturated ketone 16. Because of their thermal instability sulfoxides easily undergo elimination. The mechanism is explained by Cram as stereospecific cw-elimination. ... 

Olefins with hindered double bonds may be transformed stereospecifically to oxiranes by treatment with ozone. The epoxidation of propylene has been achieved with alkoxyalkyl-hydroperoxides obtained by the ozonization of olefins in the presence of alcohol.The yield depends on whether the alcohol is a primary, secondary, or tertiary one. The low-temperature (—70°) epoxidation of olefins with a yield of about 30% has been performed with electrophilic intermediates produced in the course of the ozonization of alkynes these intermediates are probably five-membered cyclic trioxides. This epoxidation is almost totally stereospecific. 

The results of recent investigations S of model systems provide compelling evidence that stabilized atomic oxygen is present in Compound I and Compound II of horseradish peroxidase. Thus, the combination of tetrakis(2,6-dichlorophenyl)-porphinato-iron(ni) perchlorate (6, Scheme 4-4) with pentafluoro-iodosobenzene, zn-chloroperbenzoic add, or ozone in acetonitrile at -35°C yields a green porphyrin-oxene adduct (7). This species, which has been characterized by spectroscopic, magnetic, and electrochemical methods, cleanly and stereospecifically epoxidizes olefins (>99% exo-norbornene-oxide). 

The stereospecificity of the hydrocarbon ozonation was investigated by measuring the isomer distribution of tertiary alcohols formed on ozonating cis- and fmri5-l,2-dimethylcyclohexane and cis- and trans-DecR-lin. Other oxidation products are formed in these ozonations, but the tertiary alcohols are easily separated from these by gas chromatography. Some results are shown in Table II. The observed isomer distributions of tertiary alcohols are independent of time for up to 3 hours ozonation... 

The effect of various additives on the isomer distribution of tertiary alcohols, obtained from ct5-l,2-dimethylcyclohexane, was investigated to determine the reason for the lack of complete stereospecificity in the ozonation. The results are summarized in Table III. None of the addi-... 

Ozone hydro gen peroxide Carboxylic acids from phenols Stereospecific ozonolysis... 

D-Glucose orthoesters of complex alcohols can be easily obtained with the help of silver salicylate Alcohols and amines can be conveniently prepared from olefins by ozonization-reduction and ozoni-zation-reductive amination respectively without isolation of intermediates Inverted amines can be obtained from optically-active alcohols through stereospecific formation of N-alkylphthalimides 3-Methoxy-l-phenyl-l-propyne has been used as starting material for the synthesis of a,/ -unsatd. carbonyl compounds through allenic di-carbanions a-Ketocarboxylic acids can be easily prepared from cyanohydrins through a Ritter reaction... 

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