Decarbalkoxylation

The extended ylides 270 react with electrophiles at the end of the side chain, as shown in Scheme 9 (92H(34)1005). The most unusual reaction is the nitration which requires a decarbalkoxylation, but the structure 271 is confirmed by X-ray diffraction. 

In general the -alkylation can be suppressed by using excess malonic ester 1. Another side-reaction is the decarbalkoxylation, whereby dialkyl carbonates 6 are formed ... 

Banks (151) has reported the decarbalkoxylation (NaCl in wet DMSO at 148-153°C) of the geminal diesters 490 and 493. He found that the reaction of 490 was highly stereoselective yielding the axial isomer 491 in preference to the more stable equatorial isomer 492 (ratio =9 1). On the other hand, the reaction of 493 was non-stereoselective (ratio =1 1 of 494 and 495). 

Miscellaneous. Brucine greatly accelerates the decarboxylation of certain p-oxo carboxylic acids at rt (eq 15), as well as the decarbalkoxylation of p-oxo esters. In some cases the products of these reactions possess some (modest) enantiomeric excess. ... 

The alkylation of p-keto ester enolates followed by decarboxylation affords substituted ketones (acetoacetic ester synthesis). The ester group acts as a temporary activating group. Retro-Claisen condensation can be a serious problem during hydrolysis of the ester, particularly in basic solution if the product has no protons between the carbonyl groups. In these cases, the hydrolysis should be carried out under acidic conditions or using one of the methods of decarbalkoxylation described in the next section. 

In addition to the classic sequence of saponification-acidification followed by heating, the decarboxylation of (3-keto esters can be effected by more direct methods such as decarbalkoxylation. For example, heating (3-keto esters in the presence of lithium halides in H2O-DMSO25 or in H20-collidine produces ketone products in one-pot transformations, as shown below. 

Other procedures for decarbalkoxylation include heating P-keto esters in the presence of boric acid or 4-(//,A -dimethylamino)pyridine (DMAP) in HjO-tolueneP This latter approach is also useful for the decarboxylation of a,a-disuhstituted P-keto esters, which are prone to undergo cleavage via retro-Claisen condensation. 

After the conjugate addition, activating groups such as an ester or a sulfone often are removed by decarbalkoxylation or desulfonation methods, respectively, to afford the cyclic products. 

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. 

Bernard, A., Cerioni, G., Piras, P. P. Mechanism of decarbalkoxylation of arylmethylenepropanedioic acid dimethyl esters. Tetrahedron 1990, 46, 3929-3940. 

Decarbalkoxylation H2O, DMSO water, salts, DMSO H2O, NaCl, DMSO, A... 

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... 

Decarbalkoxylation of carbamates. Bidentate carbamates such as A-carbalk-oxylactams react smoothly. Note that the use of NaOMe instead of Mg(OMe)2 leads to lactam cleavage. 

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. ... 

N-Condensed 3-pyrrolidone ring synthesis Michael addition combined with Dieckmann cyclization Subsequent -decarbalkoxylation... 

Decarbalkoxylation with triethylenediamine, l,5-diazabicyclo[4.3.0]non-5-ene (s. Synth. Meth. 29, 963), or 3-quinuclidinol in o-xylene is advantageous in cases where the usual hydrolytic conditions are precluded because of the presence of sensitive moieties, as well as for compds. not soluble in aq. solvents. E., also monodecarbalkoxylation of hindered gem. diesters by triethylenediamine, s. D. H. Miles and B.-S. Huang, J. Org. Chem. 41, 208 (1976) s. a. Synth. Commun. 5, 341 (1975). 

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