Pirrolin-2-onas e 2-pirrolidinonas são subunidades geralmente encontradas na estrutura de vários produtos naturais bioativos e 3-pirrolin-2-onas são valiosos materiais de partida em síntese orgânica devido à habilidade de reagirem como aceptores em reações de adição conjugada. Neste artigo relatamos os resultados iniciais do estudo realizado objetivando as sínteses de 3-pirrolin-2-onas reativas em reações de adição conjugada e a preparação de um precursor potencial para a síntese do nootrópico (+/-)-nebracetam.Pyrrolin-2-ones and 2-pyrrolidinones are moieties often found in the structure of several biologically active natural products and 3-pyrrolin-2-ones are valuable starting materials in organic synthesis due to their ability to react as acceptors in conjugate addition reactions. In this article we report the initial results about the performed study aiming at the syntheses of reactive 3-pyrrolin-2-ones in conjugate addition reactions and the preparation of a potential precursor for the synthesis of the nootropic (+/-)-nebracetam.

Eremantina (1), uma substância natural abundante, foi transformada em quatro etapas no diol 5. Após hidrogenólise de 5 (55 psi de H 2 , Pd/C, 30 min) obteve-se 7. Hidrogenação de 5 usando-se uma baixa pressão de hidrogênio (5 psi) e um menor tempo de reação (15 min) forneceu uma mistura de 6 e 7 (3:1). Os compostos 6 e 7 foram, a seguir, transformados nas respectivas α-metileno-γ-lactonas miqueliolido (9) e 1(R),10(R)-diidromiqueliolido (8), após eliminação de metanol.Eremanthine (1), an abundant natural substance, was transformed in four steps into diol 5. Hydrogenolysis of 5 (55 psi of H 2 , Pd/C, 30 min) furnished 7. Hydrogenation of 5 using a low hydrogen pressure (5 psi) and a short reaction time (15 min) led to a mixture of 6 and 7 (3:1). Compounds 6 and 7 were then transformed respectively to the α-methylene-γ-lactones micheliolide (9) and 1(R),10(R)-dihydromicheliolide (8), after elimination of methanol.

As α-metileno-γ-lactonas 4(15)-diidroeremantina (8), 4(15),9(10)-tetraidroeremantina (9), isoeremantina (10), acetato alílico Δ 1,10 (11), 1(R),10(R)-diidromiqueliolido (12) e 4α-hidróxi acetato alílico Δ 1,10 (13) foram sintetizadas a partir do produto natural abundante eremantina (1). Essas substâncias foram submetidas à reação de hidrólise com KOH aquoso e os sais carboxílicos dessas lactonas tiveram suas hidroxilas ativadas na posição C-6, pela formação dos respectivos mesilatos (MsCl, Et 3 N, THF ou DMSO) para deslocamento nucleofílico efetuado pelo grupo carboxilato. A utilidade dessa metodologia foi investigada para a obtenção de guaianolidos com fusão lactônica cis na posição C6-C7 e para sintetizar um precursor para estudo posterior da transformação biomimética de guaianolidos em pseudoguaianolidos.The α-methylene-γ-lactones 4(15)-dihydroeremanthine (8), 4(15),9(10)-tetrahydroeremanthine (9), isoeremanthine (10), allylic acetate Δ 1,10 (11), 1(R),10(R)-dihydromicheliolide (12) and 4α-hydroxy allylic acetate Δ 1,10 (13) were synthesized from the abundant natural product eremanthine (1). These substances were submitted to hydrolysis reaction with aqueous KOH and the carboxylic salts of these lactones had their hydroxy groups activated at the C-6 position by formation of respective mesylates (MsCl, Et 3 N, THF or DMSO) which underwent further displacement by carboxylate group. The utility of this methodology was investigated in order to obtain guaianolides with cis lactonic fusion at the C6-C7 position and to synthesize a precursor for posterior study of the biomimetic transformation of guaianolides into pseudoguaianolides.

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The sesquiterpene lactones guaia-1(10),11(13)-dieno-4α-hydroxy,9α-acetyl-15-iodine-12,6α-lactone (2), guaia-1(10),4(15),11(13)-trieno-9α-hydroxy-12,6α-lactone (3), (11S)-guaia-4(15),10(14)-dieno-9α-hydroxy-13-methoxy-12,6α-lactone (4), (11S)-guai-1(10)-eno-4α,9α-dihydroxy-13-methoxy-12,6α-lactone (5), and guaia-1(10),11(13)-dieno-4α,9α-dihydroxy-15-iodine-12,6α-lactone (6) were previously obtained starting from the natural product eremanthine (1). In this paper we report the catalytic hydrogenation reactions of allylic derivatives 2–5 and the methanol addition to α-methylene-γ-lactone of the iodohydrin 6.

The several aspects on the chemistry of eremanthine such as isolation, structural classification, biological activity, synthesis, and chemical transformations in other sesquiterpene lactones are described in this review. The main publications on this sesquiterpenolide, from its isolation of natural sources in 1972 to the current days, are included.

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The chemical reactivity of 2-pyrrolidinones and 3-pyrrolin-2-ones was evaluated in reactions of addition, nucleophilic substitution, elimination, and reduction as well as the protection of the lactamic nitrogen.