Cicloprogramação de 1,3-dienos substituidos pela reação de Simmons-Smith

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

The cyclopropanation of 1,3-diene by the Simmons-Smith reaction is normally inefficient and generates very low yields in products. The objective of this work was to verify the reactivity, site-selectivity, and stereospecificity of cyclopropanation of substituted 1,3-dienes, under drastic conditions of pressure (up to 4 kbar) and temperature (from 80 to 120°C), conducted into an autoclave, utilizing only ethyl ether as a solvent. The cyclopropanation of 2,5-dimethyl-2,4-hexadiene with methyI dibromoacetate yielded methyI chrysanthemate with a trans/cis ratio of 2.2. The best yield was obtained with the slow addition of methyl dibromoacetate, forming 21 % of products with a trans/cis ratio of 2.3, which is approximately twice the yield of that obtained for the same reaction using ethyl diiodoacetate. The cyclopropanation of methyI sorbate with diiodomethane had a 7% yield (3 isomers) with a selectivity of 71% for the ester trans-2-methyl-(2 -carboxymethyI)vinylcyclopropyl. The same reaction with dibromomethane did not result in cyclopropanated products. The deactivation of the C=C double bond with the carboxyl group was shown using the cyclopropanation of methyl sorbate and methyl muconate which yield 0.9 and 4 % of products, respectively. However, the cyclopropanation of 2,5-dimethyl-2,4-hexadiene with diiodomethane yielded 29% of cyclopropanated products, showing the activation of C=C double bond by alkyl substitution. The cyclopropanation of trans,trans-2,4-hexadiene-1-ol with diiodomethane under the same conditions is very fast and exothermic, carbonizing the compounds. The same reaction under mild conditions (reflux with ethyl ether at atmospheric pressure) produced 18% of cyclopropanated products. Under these conditions the reaction is stereoselective, forming only the trans isomer. The cyclopropanation occurred at the 2,3 positions of the diene, with a selectivity of 100%, demonstrating that the hydroxymethyl group directs the addition of the carbene to this double bond. It was not possible to synthesize the 2,2-dimethyl-3-(1 -propenyl)cyclopropylcarbinol from the trans, trans-2,4-hexadiene-1-ol and 2,2-dibromopropane, under either mild or drastic conditions. ln conclusion the substitution of the 1,3-dienes caused important effects (such as stereo and site selectivity) for the reactivity of the reagents described above. The relative activity of the substitutes is hydroxymethyl>methyl>carboxyl.

ASSUNTO(S)

piretroides sinteticos compostos organometalicos

ACESSO AO ARTIGO

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