RESUMO
A practical sequence involving a noncryogenic stereospecific boronate rearrangement followed by a robust formylation with an in situ generated DCM anion has been developed for the asymmetric construction of an all-carbon quaternary stereogenic center of a FLAP inhibitor. The key boronate rearrangement was rendered noncryogenic and robust by using LDA as the base and instituting an in situ trapping of the unstable lithiated benzylic carbamate with the boronic ester. A similar strategy was implemented for the DCM formylation reaction. It was found that the 1,2-boronate rearrangement for the formylation reaction could be temperature-controlled, thus preventing overaddition of the DCM anion and rendering the process reproducible. The robust stereospecific boronate rearrangement and formylation were utilized for the practical asymmetric synthesis of a chiral quaternary FLAP inhibitor.
Assuntos
Inibidores da Proteína Ativadora de 5-Lipoxigenase/síntese química , Compostos de Boro/química , Carbamatos/química , Inibidores da Proteína Ativadora de 5-Lipoxigenase/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
An enantioselective copper-catalyzed asymmetric conjugate addition of Me2Zn to (Z)-nitroalkenes led to the formation of all-carbon quaternary stereogenic centers with high stereoselectivity. The key features of the new method are the unprecedented use of [(MeCN)4Cu]PF6 in conjunction with the Hoveyda ligand L1 and the use of (Z)-nitroalkene substrates so that undesired nitroalkene isomerization is minimized and enantioselectivity is enhanced dramatically. We also describe a novel, practical, and highly (Z)-selective nitroalkene synthesis.
Assuntos
Alcenos/química , Cobre/química , Nitrogênio/química , Compostos Organometálicos/química , Catálise , Cromatografia Líquida de Alta Pressão , Isomerismo , Ligantes , EstereoisomerismoRESUMO
A practical, one-step process for the synthesis of 2,5-disubstituted pyrimidines is presented. The protocol proved to be general for the synthesis of a variety of pyrimidine-containing compounds bearing an assortment of functional groups.
Assuntos
Nitrilas/química , Pirimidinas/síntese química , Estrutura Molecular , Pirimidinas/químicaRESUMO
The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.
Assuntos
Toxinas Marinhas/síntese química , Compostos de Espiro/síntese química , Aldeídos/química , Ânions/química , Carbono/química , Catálise , Quelantes/química , Compostos de Iodo/síntese química , Compostos de Iodo/química , Espectroscopia de Ressonância Magnética , Toxinas Marinhas/química , Metilação , Modelos Moleculares , Estrutura Molecular , Compostos de Espiro/química , Estereoisomerismo , Sulfonas/química , Compostos de Vinila/químicaRESUMO
A Michael equilibration model is presented to provide for site-selective pyrazole condensations between alkoxyacrylonitriles and hydrazines. Both pyrazole isomers were accessed with high selectivity by employment of kinetically or thermodynamically controlled conditions. Substrate scope and identification of Michael intermediates, as well as competitive pathways, support the presented mechanistic proposal. Sandmeyer derivatization provided site-selective access to fully substituted pyrazoles.
Assuntos
Pirazóis/síntese química , Cinética , Modelos Moleculares , Estrutura Molecular , Pirazóis/química , TermodinâmicaRESUMO
[reaction: see text] A highly useful sequence of reactions is described here. These reactions consist of the first successful base-induced isomerizations of propargyl amides to chiral ynamides, applications of these novel ynamides in ring-closure metathesis leading to chiral 2-amidodienes useful for Diels-Alder cycloadditions, and the first successful tandem RCM of diene-ynamides.
RESUMO
The first asymmetric Ficini-Claisen rearrangement using chiral ynamides is described. At relatively low temperatures, the Ficini-Claisen rearrangement can be efficiently promoted by p-nitrobenzenesulfonic acid leading to high diastereoselectivity for a range of different allylic alcohols and chiral ynamides. [reaction: see text]
RESUMO
[reaction: see text] The first successful Sonogashira coupling of ynamides with aryl and vinyl iodides is described here. This study resolves the problem of the competing pathway involving homocoupling of ynamides and provides a practical entry to novel urethane- or sulfonamide-terminated conjugated acetylenic systems. An interesting tandem hydrohalogenation and Sonogashira coupling was also observed to give an en-ynamide.
RESUMO
[reaction: see text] A highly stereoselective Saucy-Marbet rearrangement using chiral ynamides and propargyl alcohols is described here. This rearrangement can be catalyzed by para-nitrobenzenesulfonic acid leading to high diastereoselectivities for a range of different chiral propargyl alcohols and ynamides in a stereochemically intriguing matched, mismatched, or indifferent manner. This provides an excellent entry to highly substituted chiral homoallenyl alcohols.
RESUMO
A highly stereoselective preparation of novel chiral (E)-alpha-haloenamides under mild conditions utilizing magnesium halide salts is described. This unexpected mild and efficient hydrohalogenation reaction highlights another synthetic utility of ynamides. [reaction: see text]
RESUMO
A practical noncryogenic process for the Aggarwal stereospecific boronate rearrangement with chiral secondary benzylic carbamates has been developed. The use of LDA instead of sec-BuLi combined with an in situ trapping of the unstable lithiated carbamate was critical to success. Furthermore, this new process increased the substrate scope to include the versatile aryl iodide and bromide substrates. The methodology was applied to a diverse array of substrates and was demonstrated on multikilogram scale.
Assuntos
Compostos de Benzil/química , Ácidos Borônicos/síntese química , Carbamatos/química , Ácidos Borônicos/química , Ésteres , Estrutura Molecular , EstereoisomerismoRESUMO
A substituted anthraquinone (AQ), previously shown to photochemically generate benzaldehyde in methanol solution, was attached to a commercially available resin via an 11 carbon tether and an amide bond. Photolysis of the polymer-bound AQ with visible or 350 nm UV light resulted in the formation of benzaldehyde in yields of 50-55% as determined by HPLC. The phenolic positions in the polymer were then alkylated using benzyl bromide and 1-iodo-3-(4-nitrophenyl)propane in a coupling reaction with K(2)CO(3) as a base and a solution-phase proton shuttle. Photolysis of these alkylated polymers resulted in the formation of benzaldehyde (54-89%) and 3-(4-nitrophenyl)-propanal (58-67%). The yields of both aldehydes dropped considerably with subsequent realkylation and photolysis, and the polymer beads began to show signs of deterioration. This is the first time that aldehydes have been made photochemically on a solid-supported phase.
RESUMO
A copper-catalyzed new C-N bond formation involving a sp-hybridized carbon is described here leading to a facile entry for syntheses of chiral ynamides. This direct N-alkynylation of amides should have a significant impact on the future development of synthetic methodologies employing ynamides.