RESUMO
A formal [3 + 2]-cycloaddition involving the Lewis acid mediated reaction of alpha-silyloxy aldehydes and styrenes to afford 3-alkyl-2-aryltetrahydrofuran-4-ols has been developed. This methodology was applied to the total synthesis of the naturally occurring furofuran lignan (+/-)-paulownin.
Assuntos
Hidrocarbonetos Aromáticos com Pontes/síntese química , Furanos/síntese química , Lignanas/síntese química , Aldeídos/química , Hidrocarbonetos Aromáticos com Pontes/química , Furanos/química , Lignanas/química , Espectroscopia de Ressonância Magnética/métodos , Estereoisomerismo , Estirenos/químicaRESUMO
The stereoselective synthesis of (-)-methyl palustramate, a possible intermediate for the synthesis of (+)-palustrine, is described. The key step of the synthesis is a conformationally restricted Claisen rearrangement to afford the highly functionalized 1-benzylpipecolic ester 10. In addition, a new procedure for debenzylation of 1-benzylpiperidines (Li, (NH(2)CH(2))(2), Et(3)N, THF) was used to remove the benzyl protecting group where traditional methods failed.
RESUMO
Indolizidine type alkaloids have been attractive synthetic targets due to their biological activity. The total synthesis of (-)-indolizidine 195B via a general route, which could potentially be used to prepare other indolizidine alkaloids such as (-)-gephyrotoxin 223AB and (-)-myrmicarin 237A, is described.
Assuntos
Indolizinas/síntese química , Indolizinas/química , Conformação Molecular , Estrutura Molecular , EstereoisomerismoRESUMO
A new approach to the synthesis of indolizidine and pyrrolizidine skeletons is reported. (-)-Lentiginosine and (1R,2R,7aR)-dihydroxypyrrolizidine have both been synthesized in 13 steps from di-O-isopropylidene-d-mannitol. The common key intermediate is (-)-dihydroxyproline benzyl ester 10.
Assuntos
Alcaloides/química , Prolina/química , Alcaloides de Pirrolizidina/síntese química , Alcaloides de Pirrolizidina/química , Espectrometria de Massas de Bombardeamento Rápido de Átomos , EstereoisomerismoRESUMO
A general synthesis approach to pyrroloquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]quinolizines) via a münchnone 1,3-dipolar cycloaddition is reported. The approach was applied to the synthesis of an unnatural pyrroloquinolizidine homologue of myrmicarin 215B.
Assuntos
Compostos Heterocíclicos com 3 Anéis/química , Pirróis/síntese química , Quinolizinas/síntese química , Alcaloides Indólicos/químicaRESUMO
The synthesis of a series of 3-hydroxyproline benzyl esters from alpha-alkyl and alpha-alkoxy N-protected aminoaldehydes with benzyl diazoacetate is described. Aldehydes with alpha-alkyl substituents afforded prolines as a single diastereomer with a trans-cis relative configuration in 14-77%. An alpha-tert-butyldimethylsilyloxy aminoaldehyde afforded a proline as a single diastereomer with a trans-trans relative configuration in 37% yield.
RESUMO
The stereoselective synthesis of tetrahydrofurans was achieved by formal [3+2]-cycloaddition of allyl and crotylsilanes with alpha-triethylsilyloxy aldehydes. The scope of the reaction was examined by using different alpha-substituted aldehydes and different substituents on the silicon. Tamao oxidation of the products resulted in formation of diols that are easily functionalized allowing an entry to natural products synthesis. The formal total synthesis of the muscarine alkaloids (-)-allomuscarine and (+)-epimuscarine was achieved.
Assuntos
Aldeídos/química , Alcaloides/síntese química , Furanos/síntese química , Muscarina/análogos & derivados , Silanos/química , Alcaloides/química , Compostos Alílicos/química , Furanos/química , Espectroscopia de Ressonância Magnética/métodos , Muscarina/síntese química , Oxirredução , EstereoisomerismoRESUMO
The reaction of a series of beta-(triethylsilyloxy)aldehydes with several allylsilanes and crotyldimethylphenylsilane is described. Aldehydes possessing an alpha-stereocenter afforded tetrahydropyrans as mixtures of two diastereomers with allylsilane, but only a single diastereomer was observed in the case of crotylsilanes. The reaction time for crotylsilanes was longer than that for allylsilanes likely due to the increased steric hindrance. Allylsilanes afforded tetrahydropyrans in 34-67% yields, and crotylsilanes provided products in 0-62% yields.