Carbonyl compounds carbon-oxygen bond cleavage

Use has been made of the bond cleavage processes initiated by an adjacent carbonyl function for the modification of steroidial ketols such as 18 [97], Reduction in ethanol eliminates the hydroxyl function and in the same reaction, the carbonyl function is reduced to a secondary alcohol. In compound 19 where there are several groups to act as electrophores, carbon-oxygen bond cleavage is initiated from the most easily reduced dienone function [98], Cleavage of the carbon-oxygen bond in an a-acetoxycarbonyl function is achievable in good yields from multifunctional compounds such as the sesquiterpene taxol [99]. 

A completely different approach to lithium homoenolate synthons uses a carbon-oxygen bond cleavage. Lithiation of acrolein diethyl acetal 180 with lithium and a catalytic amount of DTBB (2.5%) in the presence of different carbonyl compounds in THF at 0°C gave, after final hydrolysis, the corresponding y-products 181 in different diastereomeric ratios (Z/ 3/1 to 20/1) (Scheme 63) . 

Cyclic alkyl aryl ethers lead also to functionalized organolithium compounds by reductive carbon-oxygen bond cleavage in arene-catalyzed lithiation process. Thus, the treatment of 2,3-dihydrobenzofuran (47) with an excess of lithium in the presence of a catalytic amount of DTBB in THF at 0°C gives the dianion (48) which after reaction with different carbonyl compounds and final hydrolysis with water leads to... 

Thermal decomposition of dihydroperoxides results in initial homolysis of an oxygen—oxygen bond foUowed by carbon—oxygen and carbon—carbon bond cleavages to yield mixtures of carbonyl compounds (ketones, aldehydes), esters, carboxyHc acids, hydrocarbons, and hydrogen peroxide. 

The cleavage of a carbon-carbon double bond by oxidation with ozone (as ozonised oxygen) followed by hydrolysis to yield carbonyl compounds is a reaction sequence of considerable importance. This reaction, for example, can be... 

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