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1.
Org Lett ; 11(14): 2972-5, 2009 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-19548698

RESUMO

The hydride transfer initiated cyclization ("HT-cyclization") of aryl alkyl ethers, which leads to direct coupling of sp(3) C-H bonds and activated alkenes, is reported. Readily available salicylaldehyde derived ethers are converted in one step to dihydrobenzopyrans, an important class of heteroarenes frequently found in biologically active compounds. This process has not been previously reported, in contrast to known HT-cyclizations of the corresponding tert-amines ("tert-amino effect" reactions).


Assuntos
Cromanos/síntese química , Éteres/química , Hidrogênio/química , Alcenos/síntese química , Alcenos/química , Catálise , Cromanos/química , Técnicas de Química Combinatória , Ciclização , Estrutura Molecular
2.
J Am Chem Soc ; 131(2): 402-3, 2009 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-19099474

RESUMO

C-H bond functionalization enables strategically new approaches to the synthesis of complex organic molecules including biologically active compounds, research probes and functional organic materials. To address the shortcomings of transition metal catalyzed processes, we have developed a new approach to direct coupling of sp(3) C-H bonds and alkenes based on Lewis acid-promoted hydride transfer. Activation of alpha,beta-unsaturated aldehydes and ketones with Lewis acid triggers intramolecular hydride transfer, leading to a zwitterionic intermediate, which in turn undergoes ionic cyclization to afford the cyclic alkylation product. The scope of this method is expanded by the generation of alkenyl-oxocarbenium species as highly activated alkene intermediates capable of abstracting a hydride from unreactive carbon centers, including benzyl-, allyl-, and crotyl-ethers, as well as primary alkyl ethers, at room temperature. The alkenyl acetal and ketal substrates show dramatically faster rates of cyclization, as well as improved chemical yield and diastereoselectivity, compared to the corresponding carbonyl compounds. Furthermore, the use of boron trifluoride etherate as the Lewis acid and ethylene glycol as the organocatalyst provides a highly active catalytic system, presumably via the in situ formation of alkenyl-oxocarbenium intermediates, which eliminates the need for expensive transition metal Lewis acids or the preparation of ketal substrates. This binary catalytic system greatly improves the efficiency of the hydride transfer-initiated alkylation reactions.


Assuntos
Alcenos/química , Boranos/química , Éteres Cíclicos/síntese química , Cetonas/química , Alquilação , Ciclização , Cetonas/síntese química
3.
J Am Chem Soc ; 127(35): 12180-1, 2005 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-16131169

RESUMO

A practical method for the intramolecular hydroalkylation of electron-deficient olefins has been developed. The direct transformation of benzylic, tertiary, and sterically hindered secondary sp3 C-H bonds into C-C bonds under the action of a catalytic amount of a variety of Lewis acids is described. The mechanism of these transformations is proposed to involve a tandem hydride transfer/cyclization sequence.


Assuntos
Ácidos/química , Alcenos/química , Carbono/química , Hidrogênio/química , Alquilação , Catálise , Elétrons , Modelos Químicos , Oxirredução , Temperatura
4.
Synlett ; 13: 2403-2405, 2004 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-19079634

RESUMO

The epoxidation of electron deficient olefins is demonstrated with PhIO and an assortment of enones.

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