Ethyl 3,3-dimethylacrylate → Ethyl-4-bromo-3-methyl-but-2-enoate (E/Z; 55/45)

Beteiligte Stoffe

Reaktionsschritte

The olefins 66 can also be prepared by reacting the corresponding substituted phenols with ethyl 4-bromo-3-methyl-2-butenate in the presence of potassium carbonate and small amount of 18-crown-ether in methylene chloride. The starting material ethyl 4-bromo-3-methylbutenate has been obtained from the reaction of ethyl 3,3-dimethylacrylate with N-bromosuccinimide (NBS) as follows: to 20 g of ethyl 3,3-dimethylacrylate in 250 ml of carbon tetrachloride, 30 g of N-bromosuccinimide (NBS) and 0.01 g of azobisisobutyronitrile were added. The mixture was refluxed for 3 hours. Succinimide was removed by filtration and the filtrate was washed with chloroform. The combined organic layers were washed sequentially with saturated sodium sulfite, saturated sodium chloride and then dried over anhydrous magnesium sulfate. Evaporation of the solvent afforded 34.4 g ethyl 4-bromo-3-methyl-2-butenate (Safaryn, J. E.; Chiarello, J.; Chen, K. M.; Joullie, M. M.; Tetrahedron, 1986, 42, 2635). The product can be further purified by silica gel flash column chromatography using ether/hexane (e.g. 1:50) as eluent, and hydrolyzed to the corresponding carboxylic acid with aqueous methanolic NaOH. ##STR12## wherein R1 =H, CF3, R or OR;

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