Estudo das reações de X diazocetonas com enaminonas. Reatividade e utilidades sinteticas. Novo metodo de sintese de pirrois

AUTOR(ES)
DATA DE PUBLICAÇÃO

1988

RESUMO

The diazodiphenylethanone (1) reacts with the acyclic enaminones 2 to form the products of diphenylketene electrophilic attack on the Ca (3) and/or the nitrogen (4 and 5) position of the enaminone system. The cyclic enaminones 6 showed greater preference for reaction on nitrogen to form products 12 in comparison to Ca reaction products (13). The reactivities of the different acyclic enaminones 2 studied were consistent with HOMO energies determined by the HAM/3 method, while the AM-1 method showed only partial agreement. The differences in site seletivity observed for enaminones 2 and the greater preference of enaminones 6 to react on nitrogen could be explained in terms of HOMO coefficients in conjunction with steric arguments. The reactions of cyclic enaminones 6 with a- diazoketone 1, 1-diazo-1-phenyI-2-propanone (7), 2-diazo-1-phenyl-1-propanone (8) and 3-diazo-2-butanone (9) in the presence of the catalyst Cu(acac)2 yielded the corresponding ketocarbene reaction products on the nitrogen of these enaminones (15, 17, 19 and 22) and/or the pyrroles 16, 18, 20 and 23. Treatment of the compounds 15. 17, 19 and 22 with KOH in ethanol led to the formation of the corresponding pyrroles for the compounds formed from six-membered enaminones (6a-c), but not for the five-membered (6c). The reactions of acyclic enaminones 2 and a - diazoketone 1 yielded the pyrroles 14 directly. In this case, the mechanism could either involve the electrophilic attack of the ketocarbene on the nitrogen and/or the C a position of the enaminone system. By using the a--diazoketones with different substituents (7 and 8), it could be determined that the enamino ester 2g reacted preferentially on the C a- yielding the pyrroles 25 and/or 24. The reaction of 2g with the a- -diazoketone 9 led to the formation of pyrrole 21. The formation of 1,4-dihidro-indene[1,2-b]pyrrole 26a in the catalysed reaction of the enamino ester 2g with 2-diazo-1- indanone (10) showed an important synthetic application of this new method of pyrrole synthesis, wich consists in the possibility of preparing pyrroles isomeric to the pyrroles formed by the Knorr method. The catalysed reactions of ethyl diazoacetate (11) with enaminones led to the formation of the pyrroles 31, 32 and 35 and the reaction products of the corresponding carbene on the C a position of the enaminones (36 and 37). Although we elucidated some aspects of these reactions, we could not suggest an acceptable mechanism for the formation of the pyrroles.

ASSUNTO(S)

reatividade (quimica) reações quimicas

ACESSO AO ARTIGO

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