Diazo ozonization

It was not their reactivity but their chemical inertness that was the true surprise when diazirines were discovered in 1960. Thus they are in marked contrast to the known linear diazo compounds which are characterized by the multiplicity of their reactions. For example, cycloadditions were never observed with the diazirines. Especially surprising is the inertness of diazirines towards electrophiles. Strong oxidants used in their synthesis like dichromate, bromine, chlorine or hypochlorite are without action on diazirines. Diazirine formation may even proceed by oxidative dealkylation of a diaziridine nitrogen in (186) without destruction of the diazirine ring (75ZOR2221). The diazirine ring is inert towards ozone simple diazirines are decomposed only by more than 80% sulfuric acid (B-67MI50800). 

A method for synthesis of ozonides that involves no ozone has been reported. It consists of photosensitized oxidation of solutions of diazo compounds and aldehydes. Suggest a mechanism. 

Diazene, furan ozonide decomposition, 730 Diazo compounds, ozone adducts, 734 Diazonium salts, TEARS assay, 667 Dibenzoyl peroxide, determination, 698 Z-Dibenzoylstilbene, tetracyclone bleaching, 734-5... 

Carbacephalosporins The ketene-imine cyclization described above has been extended to a synthesis of a chiral carbacepham (4). This synthesis uses a dihy-droanisole group as the equivalent of a p-keto ester. Thus the azetidinone 1, obtained in 80% yield by the above route, was reduced and acylated in situ to provide 2. Ozonization followed by a rhodium-catalyzed cyclization of an a-diazo-P-keto ester provides 3, which is a useful intermediate to various substituted car-bacephams such as 4. 

Conventional treatment processes for these dyes prior to discharge involve ozonation. While a simple water-soluble monoazo dye such as A07 is easily oxidized by ozone, the larger diazo dyes such as NBB are difficult to destroy by ozonation. While oxidative ozonation is a popular treatment process, the sodium borohydride catalyzed reductive decolorization of these dyes is also used. The other example shown above, DB79, is water insoluble and is finding increased application in the dyeing of polyester and other synthetic fabrics. Traces of the disperse dye have been reported in river bed sediments in Quebec, Canada, receiving dye waste from upstream manufacturers. 

The principles underlying alternative formation of 1,2,4-trioxolanes by cyclodehydration of a,a -dihydroxydialkyl peroxides (Rieche s ozonide synthesis without ozone ), or by photooxidation of diazo compounds in the presence of aldehydes, are outlined in Table 10. 

Nickel peroxide, an undefined black oxide of nickel, is prepared from nickel sulfate hexahydrate by oxidation in alkaline medium with an ozone-oxygen mixture [929] or with sodium hypochlorite [930, 931, 932, 933]. Its main applications are the oxidation of aromatic side chains to carboxyls [933], of allylic and benzylic alcohols to aldehydes in organic solvents [929, 932] or to acids in aqueous alkaline solutions [929, 930, 932], and of aldehydes to acids [934, the conversion of aldehyde or ketone hydrazones into diazo compounds [935] the dehydrogenative coupling of ketones in the a positions with respect to carbonyl groups [931] and the dehydrogenation of primary amines to nitriles or azo compounds [936]. 

Diazo compounds are also not attacked by atmospheric oxygen at ambient temperature, although they react with ozone and in photosensitized oxygenations. 

Bailey et al. (1965) found that in a-diazocarbonyl compounds with a terminal diazo group (-CH=N2) the diazo function is replaced by an O-atom, i.e., a glyoxal derivative is formed primarily, but the final products result from CH bond cleavage. In other cases, however, the a,yff-dicarbonyl compound is stable. An example, described by Ursini et al. (1992), is the oxo-de-diazoniation (9-35) of various 6-diazopenicillanates (9.70, R = 4-NO2C6H4CH2 and other alkyl groups). The a-diketone is obtained at -15 to -10°C in dichloromethane with ozone in 86-97% yield. 

FIGURE 10.54 Like diazo compounds and ozone, a carbonyl oxide is a 1,3-dipole and adds to Jt systems to give five-membered ring compounds. 

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