Estudo da reação de Simmons-Smith : obtenção de metilenociclopropanos substituidos, de interesse industrial

AUTOR(ES)
DATA DE PUBLICAÇÃO

1995

RESUMO

The Simmons-Smith reaction is a very useful synthetic route to obtain substituted cyclopropanes from the corresponding olefins and a carbene source. Since there is no agreement in the literature with respect to the best procedure for this reaction, some parameters that influence its yield were studied. To obtain bicyclo[4,1,0]heptane (norcarane) from cyclohexene, the best conditions of the reaction are: source of carbene - methylene iodide; couple Zn:Cu - Rawson and Harrison; solvent - diethyl ether; conditions - magnetic stirring and reflux; reagents addition order - olefin followed by the carbene source; addition time of the carbene source - 4h; reaction time - 15h; zinc granulation - powder. The cyclopropanation of methylalene in di-n-butyl ether does not give cyclopropanated products. ln diethyl ether, the yield obtained, with respect to the methylalene, was 40 %, with a selectivity for methylspiropentane equal to 80% and for 2-methyl-methylenecyclopropane, 20 %. When the solvent was 1,2-dimethoxyethane, the yield fell to 30 %, while the selectivity was 60 % for the 2-methyl-methylenecyclopropane formation, 30 % for ethylidenecyclopropane and 10 % for methylspiropentane. It is concluded, thus, that the more substituted double bond is cycIopropanated more easily. The cyclopropanation of 1,2,6-cyclononatriene in diethyl ether occurred with yield of 90 %, from which 80 % were monocyclopropanated in one of the alene insaturations, while 20 % were dicyclopropanated in the other alene insaturation. The alene double bonds were more reactive for the Simmons-Smith reaction than the olefinic double bonds. Allylic alcohol were cyclopropanated with 60 % yield. The hydroxy group has no effect on the Simmons-Smith reaction and directs the methylene group to the double bond.

ASSUNTO(S)

reações quimicas tecnologia quimica

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