Krapcho decarbalkoxylation

This reaction was studied comprehensively by Krapcho beginning as early as 1967. It is an alkali halide promoted alkylative decarboxylation of active esters (e.g., )8-keto esters, fi-diesters, a-cyano esters) in polar or dipolar aprotic solvents (e.g., DMF, DMSO, HMPA,) and is generally known as the Krapcho decarboxylation or Krapcho condition. Occasionally, it is also referred to as the Krapcho decarbalkoxylation. In addition, the corresponding decarboxylation on methyl esters is known as the Krapcho decarbomethoxylation, and the decarboxylation of ethyl esters is referred to as the Krapcho decarbo-ethoxylation. ... 

Koch-Haaf Carboxylations Kochi Reaction Koenigs-Knorr Synthesis Kolbe Electrolytic Synthesis Kolbe-Schmitt Reaction Komer-Contardi Reaction Kostanecki Acylation Krafft Degradation Krapcho Decarbalkoxylation... 

Krapcho, A. P., Lovey, A. J. Decarbalkoxylations of geminal diesters, P-keto esters, and a-cyano esters effected by sodium chloride in dimethyl sulfoxide. Tetrahedron Lett. 1973, 957-960. 

Krapcho, A. P., Weimaster, J. F., Eldridge, J. M., Jahngen, E. G. E., Jr., Lovey, A. J., Stephens, W. P. Synthetic applications and mechanism studies of the decarbalkoxylations of geminal diesters and related systems effected in dimethyl sulfoxide by water and/or by water with added salts. J. Org. Chem. 1978,43, 138-147. 

Krapcho, A. P., Weimaster, J. F. Stereochemistry of decarbalkoxylation of cyclic geminal diesters effected by water and lithium chloride in dimethyl sulfoxide. J. Org. Chem. 1980,45, 4105-4111. 

In 1967, Krapcho reported the utility of a method for decarboxylating geminal diesters using a salt such as NaCN dissolved in a polar aprotic solvent like dimethyl sulfoxide (DMSO). The reaction was discovered when an attempt to effect the following substitution reaction with 1 resulted in decarbomethoxylation to give 2.2 Shortly thereafter, a comprehensive study of decarbalkoxylations using mono- and di-substituted malonates was published.3... 

These alkylation procedures can benefit greatly from the use of microwave activation, which can reduce reaction times by a factor of 60. Moreover, the often tedious separation of high boiling solvents (DMF, DMSO, HMPA) can be omitted, if reactions are conducted under solvent-free conditions in the presence of ferf-BuOK as a base and a phase transfer catalyst such as Aliquat 336. Chemical yields are comparable to those obtained using classical procedures and only traces of dialkylated byproducts have been detected. Moreover, microwave treatment of the diester product with LLF or LiCl (Krapcho procedure) under solvent-free conditions provides the corresponding mono-ester by selective decarbalkoxylation . 

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