Reduction, of ozonides, with

Acetic acid, CH3CO2H Used as a solvent for the reduction of ozonides with zinc (Section 7.9) and the a-bromination of ketones and aldehydes with Br2 (Section 22.3). 

The reduction of ozonides with triphenylphosphine,113 on the other hand, proceeds quantitatively with both ketozonides and aldozonides. Lorenz102,112 used this reaction as the basis of a method for the determination of ozonides. The reaction mechanism is probably as shown in Eq. (8).102... 

Reduction of ozonides with EtCHO JACS C197l 93 3042... 

An elegant one-pot reduction of ozonides consisting of the treatment of a crude product of ozonization of an alkene in methanol with dimethyl sulfide (36% molar excess) gives 62-97% yields of very pure aldehydes [244. ... 

Ozonides are rarely isolated [75, 76, 77, 78, 79], These substances tend to decompose, sometimes violently, on heating and must, therefore, be handled with utmost safety precautions (safety goggles or face shield, protective shield, and work in the hood). In most instances, ozonides are worked up in the same solutions in which they have been prepared. Depending on the desired final products, ozonide cleavage is done by reductive or oxidative methods. Reductions of ozonides to aldehydes are performed by catalytic hydrogenation over palladium on carbon or other supports [80, 81, 82, S3], platinum oxide [84], or Raney nickel [S5] and often by reduction with zinc in acetic acid [72, 81, 86, 87], Other reducing agents are tri-phenylphosphine [SS], trimethyl phosphite [89], dimethyl sulfide (DMS) [90, 91, 92], and sodium iodide [93], Lithium aluminum hydride [94, 95] and sodium borohydride [95, 96] convert ozonides into alcohols. 

Methyllithium reduction of ozonides appears to follow a course similar to that of Grignard reduction. Greenwood treated diethyl ozonide with isopropyl Grignard and obtained 2-methyl-3-pentanol, isopropyl alcohol, and propane in good yield (9). 

Reduction of Ozonides. In the synthesis of ecdysone from ergosterol, the ozonide product produced from (5) was reduced with (Mc2N)3P under mild conditions to the aldehyde (6) without isomerization (eq 18). The scope of this method has not been investigated. 

Aldehydes are easily oxidized to carboxylic acids under conditions of ozonide hydroly SIS When one wishes to isolate the aldehyde itself a reducing agent such as zinc is included during the hydrolysis step Zinc reduces the ozonide and reacts with any oxi dants present (excess ozone and hydrogen peroxide) to prevent them from oxidizing any aldehyde formed An alternative more modem technique follows ozone treatment of the alkene m methanol with reduction by dimethyl sulfide (CH3SCH3)... 

Commercially, pure ozonides generally are not isolated or handled because of the explosive nature of lower molecular weight species. Ozonides can be hydrolyzed or reduced (eg, by Zn/CH COOH) to aldehydes and/or ketones. Hydrolysis of the cycHc bisperoxide (8) gives similar products. Catalytic (Pt/excess H2) or hydride (eg, LiAlH reduction of (7) provides alcohols. Oxidation (O2, H2O2, peracids) leads to ketones and/or carboxyUc acids. Ozonides also can be catalyticaHy converted to amines by NH and H2. Reaction with an alcohol and anhydrous HCl gives carboxyUc esters. 

The bicyclic ozonides 12 23) and thiaozonides 13 2S) afford on catalytic hydrogenation (Pd-C) the expected 1,4-diones 61 (Eq. 47). Alternatively, deoxygenation of 12 or desulfurization of 13 with triphenylphosphine led to the same products essentially quantitatively. Both reductions served for the chemical characterization of these... 

The zwitterion (59) is thereby prevented from reacting with the ketone (58) to form the ozonide in the normal way, and both (58) and (60) may now be isolated and identified. In preparative ozonolysis it is important to decompose the ozonide (57a) by a suitable reductive process, as otherwise H202 is produced (on decomposition of the ozonide with H20, for example) which can further oxidise sensitive carbonyl compounds, e.g. aldehydes— carboxylic acids. 

One of the most common reactions for the complete cleavage of an exocyclic C-C double bond is ozonolysis. The reaction is typically performed at low temperature in dichloromethane, methanol or a mixture of both, followed by the usual reduction of the ozonide with dimethyl sulfide 15 17 80 82 i48,337 or thiourea83 to give excellent yields of the corresponding cyclobu-tanone. 

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