Ozonolysis synthetic applications

This imide system can also be used for the asymmetric synthesis of optically pure a,a-disubstituted amino aldehydes, which can be used in many synthetic applications.31 These optically active a-amino aldehydes were originally obtained from naturally occurring amino acids, which limited their availability. Thus, Wenglowsky and Hegedus32 reported a more practical route to a-amino aldehydes via an oxazolidinone method. As shown in Scheme 2 20, chiral diphenyl oxazolidinone 26 is first converted to allylic oxazolidinone 27 subsequent ozonolysis and imine formation lead to compound 28, which is ready for the a-alkylation using the oxazolidinone method. The results are shown in Table 2-6. 

Synthetic Applications. Ozonolysis, that is, the cleavage of the carbon—carbon double bond, is usually carried out in solvents, such as alcohols (methanol or ethanol), chlorinated hydrocarbons (CH2C12, chloroform), ethyl acetate, and THF, preferably at low temperature (at or below 0°C).582-584 The nature of the solvent... 

Singlet-oxygen studies have being reported to such diverse areas as chemiluminescence [14], photocarcinogenity [15], ozonolysis [16], photodynamic action [17], peroxide decomposition [7], photosynthesis [14], air pollution [18], metallocatalyzed oxygenation reactions [19,20], synthetic applications [21], and polymer degradation [10]. 

Few synthetically useful examples of the oxidation of ethers by oxygen or ozcne have been publish-ed. In 1978, Ourisson and coworkers reported that ozonization of the natural product cedrane oxide (43) on silica gel at -78 °C led to the formation of the corresponding lactone 44) in 30% yield (equation 32). A small amount of the tertiary alcohol (45) was also produced. Later, in the course of a chiral total synthesis of compactin, Hirama examined the ozonolysis of the alkene (46 equation 33). Under carefully controlled conditions, selective ozonolysis of the double bond could be achieved in 88% yield. However, when excess ozone was employed, significant amounts of the benzoate (47) were obtained, even at -78 C. In subsequent studies, benzyl ethers of primary and secondary alcohols, and carbohydrates were oxidized to the corresponding benzoates in excellent yields. Surprisingly, no further synthetic applications of this reaction have been reported. 

For synthetic applications, Whitesides and coworkers reported the first application of aqueous medium Barbier—Grignard allylation to carbohydrate synthesis using tin in an aqueous/organic solvent mixture (Eq. 4.15). Higher carbon aldoses were obtained by the ozonolysis of the deprotected allylation product, followed by suitable derivatizations. A higher diastereoselectivity was observed when a hydroxyl group was present at C-2. However, no reaction was observed under the reaction conditions when there was an N-acetyl group present at C-2 position. 

Ozonolysis has both synthetic and analytical applications m organic chemistry In synthesis ozonolysis of alkenes provides a method for the preparation of aldehydes and ketones... 

Capnellane is the generic name applied to a group of sesquiterpene alcohols and the hydrocarbon isolated from the soft coral Capnella imbricata A < >-Capnellene (667), the presumed biosynthetic precursor of the capnellenols, was first synthesized in 1981 by Stevens and Paquette Their synthetic plan called for the construction of bicyclic ketone 668 and its appropriate annulation. The latter event was achieved by application of the Rupe rearrangement to 668, conjugate addition of a vinyl group to 669, ozonolysis, and cyclization (Scheme LXVIII). Hydrogenation and olefination completed the sequence. 

Exposed multiple bonds of angular arenes are specifically prone to oxidation. The synthetic value of such double bonds arises from their high reactivity towards simple electrophiles, enophiles, and radicals. Heavy metal catalysis, periodate oxidation, and ozonolysis are the standard tools for oxidative bond cleavage in these substrates. For economic and ecological reasons, technically applicable alternatives are of great interest. Phenanthrene (29) represents a typical substrate... 

Ozonolysis of olefins has found little application in the preparation of ketones for synthetic purposes. Since the ozonides may be explosive, the method has been limited to the reaction of small quantities of olefins, mostly for degradation studies and location of double bonds. 

After reduction of the carbonyl group with sodium borohydride and protective silylation of the resulting hydroxy group, the auxiliary is removed by ozonolysis of the alkenylphos-phonamide group. By this method, or other obvious sequences, the primary products are converted into a series of enantiomerically pure, interestingly functionalized cyclopropane derivatives (Scheme 4), which should find applications as synthetic building blocks. 

Ozonolysis has both synthetic and analytical applications in organic chemistry. In synthesis, ozonolysis of alkenes provides a method for the preparation of aldehydes and ketones. When the objective is analytical, the products of ozonolysis are isolated and identified, thereby allowing the structure of the alkene to be deduced. In one such example, an alkene having the molecular formula CgHig was obtained from a chemical reaction and gave acetone and 2,2-dimethylpropanal as the products. 

Aldehydes are more easily identified than are the parent compounds, since a wide range of standards is available from commercial sources or can be prepared synthetically from other lipids. As an example of the full application of this methodology, more than 30 different bases were detected in the sphingolipids of bovine kidney [469]. Mass spectrometry can be utilised as an aid to identification of aldehydes (see also Section B above), although some workers have preferred to reduce them to fatty alcohols and then to prepare acetate or TMS ether derivatives for this purpose [624]. In addition, all the methods for the location of double bonds in fatty acids, such as ozonolysis or hydroxylation with osmium tetroxide and preparation of TMS ethers for MS, have been utilised with aldehydes prepared from sphingoid bases [464,465]. 

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