The radical decarboxylation of a Barton ester proceeds to the corresponding alkane after treatment with tributyltin hydride or t-butylmercaptan:
An alternative possibility is the introduction of a substituent by reaction with a suitable radical trapping agent:
Mechanism of the Barton Decarboxylation
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.
In addition, Barton esters can also be cleaved photolytically or thermally:
If an excess of a suitable radical trapping agent is present in the reaction medium, substitution will occur; otherwise, radical recombination takes place to give the pyridyl sulfide:
The Barton Decarboxylation offers several options for the introduction of substituents - some examples are shown below:
Synthesis of 6-functionalized tricyclodecadienones using Barton's radical decarboxylation reaction. Generation of tricyclo[5.2.1.02,6]decatrienone, a norbornene annulated cyclopentadienone
J. Zhu, A. J. H. Klunder, B. Zwanenburg, Tetrahedron, 1995, 51, 5099-5116.