Krapcho decarboxylation

The reaction proceeds by nucleophilic dealkylation of the ester by the halide followed by decarboxylation, followed by hydrolysis of the resulting stabilized carbanion.

[2] The reaction is carried in dipolar aprotic solvents such as dimethyl sulfoxide (DMSO) at high temperatures, often around 150 °C.

[3] [4][5] A variety of salts assist in the reaction including NaCl, LiCl, KCN, and NaCN.

For an α,α-disubstituted ester, it is suggested that the anion in the salt attacks the R3 in an SN2 fashion, kicking off R3 and leaving a negative charge on the oxygen.

With the addition of water, the cyanoester is then hydrolyzed to form CO2 and alcohol, and the carbanion intermediate is protonated.

The suggested reaction mechanism of α,α-disubstituted esters in the Krapcho decarboxylation reaction. R 1 , R 2 , and R 3 are any carbon containing substituents.
The suggested reaction mechanism of α-monosubstituted esters in the Krapcho decarboxylation reaction. R 2 is a hydrogen.