Cyclopropanecarboxylic esters

Cyclopropanecarboxylic esters. Reaction )f ketene silyl acetals having an allylic hydrogen with a haloform and diethylzinc in pentane results in a cyclopropanecarboxylic ester as the major product. 

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. 

The nucleophilicities of cyclopropenone acetals", bromoketene acetals and an oxaphosphorane derivative, 26, are high enough to enable reaction with some Michael acceptors. Thus, cyclopropaneacetic esters (e.g. equation 88), cyclopropanecarboxylic esters, and 1-acetyl-1-methylcyclopropanes have been generated, respectively, from these precursors. 

Silyl enol ethers of cycloalkanones are converted into spiro cydopropylmethanols with CH2l2/ZnEt2 . The reaction of ketene monosilyl acetals with CHBr3/ZnEt2 gives cyclopropanecarboxylic esters (equation 100)". 1-Cyanocyclo pro panecar boxy lie esters... 

An unprecedented cyclopropanation reaction was observed during the reaction of ketene alkylsilyl acetals (191) with bromoform-diethylzinc. When monosubstituted acetals were used, cyclopropanecarboxylic esters (195) were formed by a novel C-H insertion. When disubstituted ketene acetals were used, byproducts such as a,)5-ethylenic esters (197) were also formed presumably via 196 (equation 49). This reaction provides a convenient method for the preparation of the bicyclo[3.1.0] hexane system and can be advantageously compared to the copper-catalysed intramolecular cyclization of unsaturated a-diazoketones . 

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