Cyclopropanecarboxylic esters, synthesis

Cyclopropanecarboxylic acid may be prepared by a malonic ester synthesis, as retrosynthetic analysis shows. 

The cyanoacetic ester synthesis with ethylene bromide is preferred to the malonic ester synthesis for the preparation of cyclopropanecarboxylic acid. ... 

Cyclopropanes via abnormal Hofmann elimination. This procedure provides ethyl 1-benzylcyclopropanecarboxylate in significantly improved yield and is generally applicable to the synthesis of I-substituted cyclopropanecarboxylic esters. 

In addition to the general synthetic methods mentioned in the previous sections, this section deals with specific procedures for the synthesis of cyclopropanes which entail completely different reaction mechanisms. The acid-catalysed cyclization of the 4,6,6,6-tetrachlorohexanoic acid derivative 441 gives cyclopropanecarboxylic ester (442) (equation 149) . ... 

Cyclopropanation. The reaction of sulfonium ylides 96 with acrylic esters or methyl vinyl ketone provides rrany-2-arylcyclopropanecarboxylic esters and methyl ketones. Generation of the ylides with EtNP(NMe)2-N=P(NMe)j as base is convenient because dichloromethane can be used as solvent. Another synthesis of cyclopropanecarboxylates proceeds by a conjugate addition and 1,3-elimination sequence. ... 

With the correct choice of reaction conditions, however, the asymmetric synthesis of cis-suh-stituted cyclopropanecarboxylic acid derivatives is achieved. Stereoselective methylene transfer to (Z)-a, -unsaturated acyl systems bonded to optically active carbonyl()j -cyclopen-tadienyl)triphenylphosphanyliron 2 and oxidative decomplexation of the products gave cis-substituted cyclopropanecarboxamides 3. High asymmetric induction (up to 92% de) was observed with bromine/l-phenylethylamine as decomplexation agent. When the decomplexation was carried out with A-bromosuccinimide/ethanol, racemic cw-substituted cyclopropanecarboxylic acid esters were obtained. 

The carbenoid reaction between alkyl diazoacetates and enol ethers, enol acetates and silyl enol ethers furnishes P-oxycyclopropane carboxylates (see Tables 2, 4, 5, 6, 7 and Scheme 5). The recently recognized synthetic versatility of these donor/acceptor-substituted cyclopropanes i 2,io3) (precursors of 1,4-dicarbonyl and P, 7-unsaturated carbonyl compounds, 4-oxocarboxylic acids and esters, among others) gave rise to the synthesis of a large number of such systems with a broad variation of substituents p-acetoxycyclopropanecarboxylates , p-alkoxy- or p-aryloxysubstituted cyclopropanecarboxylates 2-alkoxy-1-methyl-1-cy-... 

Cyclopropanecarboxylic acids pr., 189 synthesis, 74-76, 136 —, esters ring opening, 69 synthesis, 74-76... 

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