Butane-2,3-diol oxidative cleavage

Fatty acids, both saturated and unsaturated, have found a variety of applications. Brassilic acid (1,11-un-decanedicarboxylic acid [BA]), an important monomer used in many polymer applications, is prepared from erucic acid (Scheme 2), obtained from rapeseed and crambe abyssinica oils by ozonolysis and oxidative cleavage [127]. For example, an oligomer of BA with 1,3-butane diol-lauric acid system is an effective plasticizer for polyvinylchloride. Polyester-based polyurethane elastomers are prepared from BA by condensing with ethylene glycol-propylene glycol. Polyamides based on BA are known to impart moisture resistance. 

Lead tetraacetate (abbreviated LTA) reacts with diols to give the same kind of oxidative cleavage. When 69 is treated with LTA, the initial cyclic product is cyclic intermediate 73, which fragments to butanal and acetaldehyde. Periodic acid gives the same cleavage reaction. Both periodic acid and lead tetraacetate are mild and effective reagents for the oxidative cleavage of diols. 

Evidence concerning the relative extents of C-C and C-H fission is less well defined for Ce(IV) and Mn(III) as compared with V(V). Pinacol is cleaved to acetone in all cases, but while Mn(IlI) pyrophosphate [like V(V)] oxidises pinacol much faster than butane-2 3-diol, the rate ratio with Ce(IV) is only approximately 3 and the production of acetaldehyde from butane-2 3-diol by Ce(IV) oxidation demonstrates C-C cleavage . It is probable, therefore, that Mn(III) oxidises the disecondary glycol by C-H fission. 

Different reactivities of some substituted oxan-4-ols on oxidation by pyridinium chlorochromate (PCC) are rationalized on the basis of their conformational features, including twist conformations.2 A rate-determining carbon-carbon bond cleavage step in a glycol-PCC complex is proposed in the oxidation of butane-2,3-diol to acetaldehyde.3 Steroidal 6/i-hydroxy-4-en-3-onc was isolated as an intermediate in the oxidation of steroidal 5-en-3/i-ol with PCC.4... 

There are subtle reactivity differences between dioxanes and dioxolanes that may be exploited in complex molecule synthesis. This can be of considerable use in the selective removal of these acetal protecting groups under oxidative conditions. A classic example is to be found in Stork s innovative synthesis of erythronolide A (Scheme 6.11) (36). Selective oxidation of 56 with ozone leads to cleavage of the dioxolane in preference to the dioxane to furnish 57. The selectivity is associated with the stereoelectronic effects (LPo<- C-H) that render the dioxolane C-H more labile. The structural differences between dioxolanes and dioxanes can also be used to gain access to protected butane-1,2,4-triol derivatives, as shown on the right [7, 9]. Thus, either 1,2- or 1,3-diols can be selectively masked as the corresponding dioxolane or dioxane, respectively, by selection of acetone or benzaldehyde as the reacting partner. 

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