Cyclopropanecarboxylic acid salts

In the following we shall focus on heterogeneous acid-base reactions. One of the best known case studies is the reaction of crystalline benzoic acid with ammonia to form 1 1 ammonium salts [19, 20]. Crystalline p-chlorobenzoic anhydride reacts with gaseous ammonia to give the corresponding amide and ammonium salt [22] a similar reaction has been investigated in the case of optically active cyclopropanecarboxylic acid crystals [23]. 

Self-condensation of the dianion of cyclopropanecarboxylic acid (450) at 50 °C affords the electrophilic cyclopropane (451). Reaction of the dianion with other carboxylate salts. 

Hunsdiecker reaction of the silver salts of both cis-(56) and trans-2-methylcyclopropanecarboxylic acid (57) yielded the same mixture of cis- (58) and trans-1-bromo-2-methylcyclopropane (59), thus demonstrating that the 2-methylcyclopropyl radical was incapable of maintaining its configuration . Brominative decarboxylation of the silver salts of exo- (60) and em/o-norcarane-7-carboxylic acid (61) produced the same mixture (16 84) of exo- (62) and entio-7-bromonorcarane (63)". Similarly, cis- and trans-silver 1,2-cyclopropanedicarboxylate gave rise to the same isomer ratio (24 76) of cis- and fraws-1,2-dibromocyclopropane. Consistent with these results is the report that the Hunsdiecker reaction with the silver salt of trans-2,2,3-d3-cyclopropanecarboxylic acid (64) gives an equimolar mixture of cis- (65) and rrans-2,2,3-d3-cyclopropane (66) . 

As far as salts of cyclopropanecarboxylic acids are concerned exceedingly low rates for the deuterium oxide catalyzed H/D exchange have been observed by Bottini and Davidson in the case of the sodium salts 213, 214 and 215. 

In agreement with these results Krapcho and Jahngen s attempts to utilize cyclopropanecarboxylic acid (216) in the reactions of a-anions of cycloalkanecarboxylic acid salts with cycloalkanones have been unsuccessful. 

Treatment of cyclobutanone under aqueous acidic conditions with either hydrogen peroxide/selenium dioxide or thallium(III) salts gives cyclopropanecarboxylic acid in a good yield (equation 176) ... 

The catalytic pair Ni(CN)2/Bu4N Br readily catalyzes the biphasic carbonyla-tion of a-haloalkynes [144, 145] and allenyl halides [145]. The first reaction results in a mixture of allenic monoacids and unsaturated diacids, whereas allenyl halides transform to allenic acids with high regioselectivity. The carbonylation of gem-dibromocyclopropanes under PTC conditions is catalyzed by Ni" and Co" salts. The reaction gives the corresponding cyclopropanecarboxylic acids in fair yields [146]. 

Cyclopropanecarboxylic acid esters by abnormal Hofmann degradation of quaternary ammonium salts via their hydroxides... 

Modified lithium aluminum hydride has been used successfully for the reduction of esters at temperatures of about 0 °C. Thus, lithium tri-f-butoxyaluminum hydride readily reduces phenyl esters of carboxylic acids to aldehydes in 33-77% yields other esters are reported to be unreactive, as are many other functional groups (acyl chlorides react with the same reagent at -70 °C, however). Phenylbenzoate and phenyl cyclopropanecarboxylate do not give the aldehyde. Iminium salt esters (11 equation 4) can be reduced with lithium tri-f-butoxyaluminum hydride (see Section 1.11.3). ... 

When treated with a tetraalkylammonium fluoride, various 1-substituted trimethylsilylcyclo-propanes are converted to tetraalkylammonium salts of the corresponding cyclopropyl anions. Such anions are trapped by performing the reaction in the presence of an aldehyde, a ketone or carbon dioxide. The reaction is carried out successfully with electron-donating and electron-withdrawing substituents a to the silyl moiety. The best yield was obtained when methyl 1-trimethylsilylcyclopropanecarboxylate was treated with tetrabutylammonium fluoride in tetra-hydrofuran and acetaldehyde, methyl l-(l-hydroxyethyl)cyclopropanecarboxylate (la) was obtained in 90% yield.Under similar conditions (Z)-2,6-dimethyl-l-[(l-trimethylsilylcy-clopropyl)methylene]cyclohex-2-ene was transformed to (Z)-l- [l-(l-hydroxy-l-methyl-ethyl)cyclopropyl]methylene -2,6-dimethylcyclohex-2-ene (2) in 90% yield in the presence of acetone.Similarly, when carbon dioxide was used as electrophile in the presence of cesium fluoride, typically 1-trimethylsilylcyclopropane-l-carbonitrile was converted quantitatively to 1-cyanocyclopropanecarboxylic acid (3a). ... 

Treatment of 3-(l-benzyloxymethylcyclopropyl)propanoic acid with various mercury(II) salts such as nitrate, trifluoroacetate and perchlorate gave the lactones 25A and 25B in 35-86% yield after aqueous potassium bromide workup. A number of related cyclopropanecarboxylic esters were reacted in the same fashion to give bromomercurio-substituted lactones 26 and 27/28 from which the mercury was removed by reduction with sodium borohydride. ... 

Silyloxycyclopropanecarboxylates are masked homoenolate equivalents which can also add to dimethyl(methylene)iminium salts. In one of several examples reported by Reissig and Lorey, methyl 2-f-butyl-2-(trimethylsilyloxy)cyclopropanecarboxylate and triflate salt (33) react to produce methylaminomethyl-y-oxo ester (64 Scheme 14). The reactive intermediate has not been precisely determined but is most likely a ring-opened enolate (63) or its silyl ketene acetal derivative. The reaction can also be performed using the chloride iminium salt (31) in the presence of TiCU, but the reproducibility is poor due to reduced solubility. The products of these reactions are convenient precursors to a-methylene-8-lactones and acrylic acid derivatives. 

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