Everton Melo dos Santos

A practical and efficient preparation of (−)-(4aS,5R)-4,4a,5,6,7,8-hexahydro-4a,5-dimethyl-2(3H)-naphthalenone: a key intermediate in the synthesis of (−)-dehydrofukinone

Abstract A novel diastereoselective route to octalone (−)- 1 has been developed. The key step involves an asymmetric Michael addition of the corresponding chiral secondary enamines derived from ( S )-(−)-1-phenylethylamine and (3 R )-2,3-dimethylcyclohexanone to methyl vinyl ketone. This enone was successfully transformed into the eremophilane-type sesquiterpenoid (−)-dehydrofukinone.

Democracia e capital social na américa latina: uma análise comparativa

The main purpose of this article is to identify societal conditions that may work to favor democracy in Latin America, articulating this concept of democrac...

Substituent influence on the diastereoselectivity of the alkylation of cyclic chiral imines

A alta diastereosseletividade, normalmente observada na reacao de alquilacao de iminas quirais derivadas de cetonas ciclicas, nao e observada no caso de cetonas com substituintes quirais. A influencia do tamanho do substituinte foi estudada com iminas preparadas a partir da (5R)-2,5-dimetilciclohexanona e (5R)-carvomentona com ambos enantiomeros da 1-feniletilamina (PEA). Usando metil vinil cetona como eletrofilo, um caso matched foi observado com a imina derivada da (S)-PEA. Entretanto, o ed depende fortemente do substituinte no caso mismatched partindo-se da (R)-PEA. O aumento do volume do substituinte leva a diminuicao do ed na ordem i Pr– < CH 2 =C(CH 3 )– < Me–. Os resultados sao explicados pela hipotese de um controle estereoeletronico a favor de um ataque axial ao tautomero enamina. O equilibrio conformacional da enamina aparenta ser crucial para explicar os dados experimentais. No caso matched somente um conformero e esperado enquanto a mistura dos conformeros e postulada no caso mismatched. The normal very high diastereoselectivity of alkylation reaction of chiral imines derived from cyclic ketones is not observed in the case of substituted chiral ketones. The influence of the substituent size was studied for imines prepared from (5R)-2,5-dimethylcyclohexanone and (5R)-carvomenthone with both enantiomers of 1-phenylethylamine (PEA). Using methyl vinyl ketone as electrophile a matched situation was observed with (S)-PEA imine derivative. However, the de is strongly dependent of the substituent in the mismatched case, starting from (R)-PEA. Enlargement of substituent size leads to lowering de in the order i Pr– < CH 2 =C(CH 3 )– < Me–. The results are reasoned by the assumption of a stereoelectronic control in favour of an axial attack at enamine tautomer. The conformational equilibrium of enamine seems to be crucial to explain experimental data. In matched case only one conformer is expected while a mixture of conformers is postulated in the mismatched one.

Aspectos regio- e estereoquímicos da adição de Michael assimétrica via iminas quirais com centros estereogênicos pré-existentes

The asymmetric Michael addition reactions using chiral imines, under neutral conditions (deracemizing alkylation process), constitute one of the main methods for the stereocontrolled elaboration of quaternary carbon centers. This protocol is based on the conjugate addition of secondary chiral enamines to electron-deficient alkenes. The focus of this report deals with the discussion of regio- and stereochemical aspects of the deracemizing alkylation process concerning enamines bearing a resident chiral center.