Cyclopropanes Knoevenagel reaction

The cz5-aziridine substrate shows, as expected on the basis of this model, predominant formation of the trans-cyclopropane product. The starting materials for this MIRC reaction can readily be obtained from the aziridine esters by reduction to the corresponding aldehyde and a subsequent Knoevenagel reaction with malonate ester (Scheme 25) [34]. 

A weak base such as glycine added to [HMIMjPFg has also been reported to catalyze a Knoevenagel reaction of malononitrile and benzaldehyde 110). A KOH-treated [BMIMjPFg also provides a suitable medium for the Corey-Chaykovsky epoxidation of enones and cyclopropanation of aldehydes using trimethyl sulfonium iodide (///). 

When these reaction conditions were employed to oxidative addition of aldehydes with 1,3-indandione 149, different type of product was obtained, the bispiro-snbstituted cyclopropanes 150 exclusively and in good yields (Scheme 2.52, Table 2.46). Model reactions carried out in dioxane solvent gave the same prodncts, but after 1 h the yields were lower. The reaction mechanism is thought to start with Knoevenagel condensation, followed by iodination, and intramolecnlar nucleophilic 0-attack with HI elimination to dihydrofurans. When intramolecnlar nucleophilic C-attack occurs, with subsequent elimination of HI, cyclopropanes were prodnced. 

A diastereoselective synthesis of cyclopropanes combines an aryl acetonitrile, ArCH2CN, with an aldehyde, RCHO, to give 100% cis-product (116) as a racemic mixture of enantiomers. " The one-pot reaction shows yields of 45-93% covering a wide range of substrates Ar includes 3-pyridyl and 2-thiophenyl, and the aldehyde can be aromatic or aliphatic. The reaction sequence consists of a Knoevenagel condensation followed by a Corey/Chaykovsky cyclopropanation. 

The reaction of potassium cyanide or sodium methoxide with the allylic bromide (34) leads to cyclization and this method appears to be a good preparation of densely substituted cyclopropanes. (In this, as in other 1,3-eliminations, the mechanism may be either stepwise or concerted and only in few cases have the mechanisms been investigated.) A new preparation of substituted spiro [2,5] octanes is based upon this reaction. Compounds (35), which are readily available by Knoevenagel condensations, react with potassium cyanide as shown in Scheme 4. It was shown that, from the -compound (35bX a single product was obtained. The authors suggest that it is the cis-compound shown. 

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