Mechanism of the hydrolysis of (Z)-4-benzylidene-2-methyloxazolin-5-one or (Z)-4-benzylidene-2-phenyloxazolin-5-one derivatives

Abstract

The methyl (la) and the phenyl (2) derivatives of (Z)-4-benzylideneoxazolin-5-one were hydrolyzed at comparable rates under alkaline conditions. In contrast, the acidic hydrolysis of 2 was at least 105 times slower than that of la. The Hammett p value obtained from the acidic hydrolysis of the phenyl substituted derivatives of la was 0.20 ± 0.09 while that from the corresponding basic hydrolysis was 1.50 ± 0.11. Methanolysis of la under basic conditions produced the methyl ester of (Z)-a-(acetylamino)cinnamic acid, and that under acidic conditions led to products consistent with the attack of methanol at the imine carbon. These results indicate that the alkaline hydrolysis of the oxazolin-5-one derivatives occurs through nucleophilic attack at the carbonyl carbon of the substrate and the acidic hydrolysis through that at the imine carbon.

Síntese e hidrólise de azalactonas de Erlenmeyer-Plöchl mediadas por radiação micro-ondas em aparelhos doméstico e dedicado: experimentos de química orgânica para a graduação

“…13 Para isto, podem ser hidrolisadas e então hidrogenadas, ou a sequência inversa. Todavia, na etapa de hidrolise é sempre empregada condição alcalina, sendo necessária uma etapa final de acidificação.…”

“…Foto dos sólidos coloridos, espectros de absorção da região do UV-Visível para 3a, espectros na região do infravermelho e espectros de RMN de 1 H e 13 C para compostos selecionados encontram-se disponíveis gratuitamente em http://quimicanova.sbq.org.br, na forma de arquivo PDF.…”

“…Neste ponto, o professor pode fazer uma comparação direta dos dois procedimentos aqui relatados com os existentes nos livros textos, demonstrando a economia atômica e o cálculo do fator E para as duas propostas de hidrólise, alcalina e ácida, onde ficam evidentes as vantagens desta última. 13 Para a análise aqui proposta, recomendamos a abordagem descrita no livro didático de Correa e Zuin 5 e o artigo de Merat e Gil, 14 pois são bem adequados à introdução destas métricas em curso de graduação.…”

Functionalization of α,β-Unsaturated Esters and Ketones: A Facile and Highly Stereoselective One-Pot Approach to N-Protected α,β-Dehydroamino Acid Derivatives

“…Several synthetic approaches to N-protected dehydroamino acids have been developed so far . However, these known methods suffer from one or more of the following drawbacks: multiple-step preparation, harsh conditions, expensive reagents, or unsatisfactory yields.…”

“…However, these known methods suffer from one or more of the following drawbacks: multiple-step preparation, harsh conditions, expensive reagents, or unsatisfactory yields. For example, expensive alkynoates and toxic phosphines are often needed for this synthesis (Scheme , eq 1) 11a. Vicinal amino alcohols are usually utilized for the two-step synthesis of dehydroamino acids (Scheme , eq 2) 11b.…”