Geminal dicarboxylic acid

The a-sulfenyl group can be replaced by a benzothiazolthio group, as demonstrated in the synthesis of the 1,4-diketone (CXXXIV), a precursor of cw-jasmone [Eq. (65)] [10]. The geminal dicarboxylic acid (CXXXVI) can also be transformed into the 1,4-diketone (CXXXIV) by electrochemical decarboxylation as in Eq. (66) [6], suggesting that the substituted malonic acid group is synthetically equivalent to a carbonyl group. 

Sol 1. (c) Geminal dicarboxylic acid (i.e., compounds in which the two carboxyl groups are on the same carbon atom) and p-ketocarboxylic acid obtained by the oxidation of diols II and IV, respectively, readily undergo decarboxylation on heating. 

In addition to cyclic allylic substrates, malonate nucleophiles have been used in reactions with both symmetrical" and unsymmetrical" acyclic systems, and with geminal dicarboxylates. Malonates and Meldrum s acid have also been used as nucleophiles in the desymmetrization of meso diesters. 

Pd - and PT-catalyzed carbonylation of geminal vinylic dibromides gives diynes or dicarboxylic acids using benzene or t-amyl alcohol as a solvent, respectively (eq. (10)) [135]. 

In Scheme 22 one can observe that stereoisomeric dicarboxylic acids are also formed (1 2 molar ratio to the monocarboxylic one) through oxidative carbonylation leading to stoichiometric liberation of palladium(O). Their formation is enhanced by the lack of geminal substituents. If oxidative conditions are used (CO -l- O2), dicarboxylated products become predominant. 

---