Barton-decarboxylation

Radical decarboxylation via the corresponding thipcarbonyl derivatives of the carboxylic acids. 

---

The allyl alcohol trapping reaction was further studied by Crich and coworkers, who applied the Barton decarboxylation reaction as radical source,... 

More recently, radical additions to fluoroethenes have attracted attention. Eguchi et al. [125] applied the Barton decarboxylation procedure to add a range of alkyl radicals to l,l-dichloro-2,2-difluoroethene. Addition was regioselective and the terminal carbon could be hydrolysed to a carboxyl group with silver(I) mediation (Eq. 39). The fluoroalkene is effectively an equivalent for either difluoroacetyl anion or cation synthons, because the adding radical can be approached from either polarity manifold. 

The initiation of the Barton Decarboxylation ( Bu3Sn-H -> Bu3Sn-) is effected with a radical initiator, and as with the Barton-McCombie Deoxygenation, the driving force for the reaction itself is the formation of the stable S-Sn bond. 

The Barton Decarboxylation offers several options for the introduction of substituents - some examples are shown below ... 

From the practical point of view, alkylation of heteroaromatics with Barton decarboxylation of A-acyloxy-2-thiopyridones (17), prepared from carboxylic acids and Af-hydroxy-2-thiopyridone, is very useful, since it can be used for various kinds of carboxylic acids such as sugars and nucleosides [23-26]. This reaction comprises of the initial homolytic cleavage of the N-0 bond in A-acyloxy-2-thiopyridone to form an acyloxyl radical and PyS , (3-cleavage of the acyloxyl radical to generate an alkyl radical and C02, addition to the electron-deficient position of heteroaromatics by the alkyl radical to form the adduct, and finally, abstraction of a hydrogen atom from the adduct by PyS , as shown in eq. 5.10. 

Barton Decarboxylation Reaction with A/-Hydroxy-2-thiopyridone... 

Stereochemistry in radical reactions for organic synthesis has not been studied very extensively, because mild or low temperature-promoted radical reaction methods are extremely limited and the stereoselectivity in radical reactions is generally rather poor. Recently, however, stereoselective organic synthesis with radical reactions has become popular, since mild radical reaction methods such as the Barton decarboxylation, Et3B-initiated Bu3SnH reaction, etc. have been developed. Normally, low temperature-initiated radical reactions induce high stereoselectivity. 

Since Barton decarboxylation can be performed under mild conditions, thermal or photolytic treatment of the Barton ester (13) of propionic acid with TV-hydroxy-2-thiopyridone in the presence of chiral menthyl acrylates generates addition products (14). However, diastereoselectivity is rather poor, since the chiral menthyl center is too far away from the C-C bond-forming position, as shown in eq. 10.7. When the chiral center is adjacent to the reaction position, stereocontrol is significantly affected, as shown in eq. 10.8 [9-12]. 

Disciplined radicals and disciplinary radical reactions (Barton decarboxylation)... 

During their studies on the stereochemistry of intramolecular 1,3-diyl trapping reaction as depicted in Scheme 13, Little and collaborators utilized the reductive decarboxylation in preparing the required compound 31.24 The usefulness of Barton decarboxylation was also realized by Braekman and colleagues during their studies on ichthyotoxic sesterterpenoids in providing the needed methyl ketone 32 from the carboxylic acid 33.25 Helmchen has developed an easy route to a stable... 

---