Heterocoupling carboxylic acids

A radical tandem cyclization, consisting of two radical carbocyclizations and a heterocoupling reaction, has been achieved by electrolysis of unsaturated carboxylic acids with different coacids. This provides a short synthetic sequence to tricyclic products, for example, triquinanes, starting from carboxylic acids which are accessible in few steps (Scheme 6) [123]. The selectivity for the formation of the tricyclic, bi-cyclic, and monocyclic product depending on the current density could be predicted by applying a mathematical simulation based on the proposed mechanism. 

Unsaturated carboxylic acids can be de-carboxylated to alkyl radicals that undergo an intramolecular addition. The S-exo-trig-cyclization of fi-allyloxy radicals, generated from an appropriate carboxylic acid, combined with a final heterocoupling has been applied to synthesize a precursor of prostaglandine PGF2q (Fig. 47) [246] and a branched carbohydrate (ratio of diastereo-mers 1.8 1) (Fig. 48) [247]. A radical tandem cyclization of a doubly unsaturated monocyclic carbocyclic acid provides a... 

Unsymmetrical compounds can also be prepared via mixed Kolbe electrolyses of different carboxylates (heterocoupling). The disadvantagous but unavoidable formation of symmetrical dimers can be suppressed to the formation of essentially one by-product if the cheapter carboxylic acid is used in a 5- to 10-fold excess. Hydrogenated carotenoids, saturated and unsaturated fatty acids, optically active )-hydroxycarboxylic acids, and intermediates for the preparation of muscone and humulene have been obtained in this way [177b]. 

The heterocoupling of carboxylic acids bearing chiral auxiliaries has been used to study the diastereoselectivity of the coupling of Kolbe radicals [204b]. For that purpose, 2-substituted malonic acid amides bound to seven different chiral auxiliaries were coelectrolyzed with different coacids [Eq. (200]- The yields in heterodimer ranged between 13 to 69%, and the diastereoselectivities between 20 and 86% de. 

A radical tandem cyclization, consisting of two radical additions and a heterocoupling reaction, has been achieved by coelectrolysis of unsaturated carboxylic acids with different coacids. This provides a short synthetic sequence to tricyclic products, such as... 

Heterocoupling of Radicals from Anodic Decarboxylation of Carboxylic Acids... 

Carboxylates with different non-racemic chiral auxiliaries have been anodically de-carboxylated to explore the face-selective hetero- and homocoupling of the intermediate radicals. 2-Substituted malonamides were subjected to heterocoupling with different coacids. In the acids 30a-c, (2/ ,5.R)-2,5-dimethylpyrrolidine served as chiral amido group. 

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