Retro-Dieckmann cleavag

SodiumIalcohol Retro-Dieckmann cleavage Dicarboxylic acid esters... 

Evidence for this postulate was provided by epimerization of deuterio-or tritio-labeled derivatives of (148) 117). As the result, a retro-aldol type mechanism in which stereoelectronic requirements are satisfied in the transition state was suggested. The process is depicted in Figure 5. This concept was also applied to the retro-Dieckmann type cleavage of ketone (151) to carboxylic acid (152) (Scheme 31), the facile epimerization of the 3p-axial alcohol (153) to the 3 a-equatorial alcohol (154) under the influence of dilute alkali (followed by esterification) and the cleavage of the 3-ketone (155) to methyl ester (156) on treatment with sodium hydroxide in methanol at 0°C for one hour (Scheme 31). 

Mahajan has described a novel route to macrocyclic ketolactones using a retro-Dieckmann reaction (Scheme 24). Although perhaps not of general applicability, the method appears attractive for the synthesis of the type of molecule shown in the scheme. The same idea of bond fission of polycyclic systems to form macro-lides has been used to prepare ketolactones from 2,3-polymethylene-benzo- and -naphtho-pyrans by oxidative cleavage (Scheme 25). 

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