RESUMO
The as-synthesized (TBA)8H5[Nd(SiW11O39)2] manifested high catalytic activity for cyanosilylation of ketones, and its catalytic activity could be improved further through rational design of the reaction micro-environment beyond the molecular level, and the corresponding mechanism has been systematically studied.
RESUMO
The enantioselective synthesis of α- and γ-tocopherol (the most biologically active members of vitaminâ E family) and analogues has been accomplished employing a new enantioselective gold catalyzed intramolecular allylic alkylation reaction followed by an olefin cross-metathesis as key steps. The methodology proved to be applicable to different olefins highlighting its potential for the synthesis of diverse libraries.
Assuntos
Álcoois/química , Cromanos/síntese química , Ouro/química , Vitamina E/análogos & derivados , Alquilação , Compostos Alílicos/química , Catálise , Cromanos/química , Estereoisomerismo , Vitamina E/síntese químicaRESUMO
Chiral contact ion-pair catalysis with particular focus on metal-free processes is gaining in interest. As a result, new perspectives are opened, and highly stereoselective transformations, traditionally performed under metal catalysis, can be realized. Herein, we report the development of an unprecedented asymmetric Brønsted acid-catalyzed allylic alkylation. The concept relies on chiral contact ion-pair catalysis, in which the chiral organic counteranion of an allylic carbocation induces high enantioselectivities and allows access to biologically relevant chromenes in good yields and with excellent enantioselection.
Assuntos
Aminas/química , Benzopiranos/química , Íons/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
We report the regiocontrolled syntheses of ethene-bridged para-phenylene oligomers in three distinct classes by using Pt(II)- and Ru(II)-catalyzed aromatization. This synthetic approach has been developed based on twofold aromatization of the 1-aryl-2-alkynylbenzene functionality, which proceeds by distinct regioselectivity for platinum and ruthenium catalysts. Variable-temperature NMR spectra provide evidence that large arrays of these oligomers are prone to twist from planarity. The UV/Vis and photoluminescence (PL) spectra as well as the band gaps of these regularly growing arrays show a pattern of extensive pi conjugation with increasing array sizes, except for in one instance.
Assuntos
Etilenos/química , Luz , Platina/química , Rutênio/química , Catálise , Eletroquímica , Espectroscopia de Ressonância Magnética , Modelos Químicos , Estrutura Molecular , Fotoquímica/métodosRESUMO
With gold and platinum catalysts, cis-4,6-dien-1-yn-3-ols undergo cycloisomerizations that enable structural reorganization of cyclized products chemoselectively. The AuCl3-catalyzed cyclizations of 6-substituted cis-4,6-dien-1-yn-3-ols proceeded via a 6-exo-dig pathway to give allyl cations, which subsequently undergo a pinacol rearrangement to produce reorganized cyclopentenyl aldehyde products. Using chiral alcohol substrates, such cyclizations proceed with reasonable chirality transfer. In the PtCl2-catalyzed cyclization of 7,7-disubstituted cis-4,6-dien-1-yn-3-ols, we obtained exclusively either bicyclo[4.1.0]heptenones or reorganized styrene products with varied substrate structures. On the basis of the chemoselectivity/structure relationship, we propose that bicyclo[4.1.0]heptenone products result from 6-endo-dig cyclization, whereas reorganized styrene products are derived from the 5-exo-dig pathway. This proposed mechanism is supported by theoretic calculations.
RESUMO
We report a new metal-catalyzed 6-endo-dig cyclization of cis-4,6-dien-1-yn-3-ols, which produces substituted benzene and naphthalene derivatives with structural reorganization. In this process, we observe a 1,3-alkylidene migration via cleavage of the olefin double bond of the starting substrates. The ease and reliability of this cyclization are manifested by its compatibility with a wide array of diverse substrates and several pi-alkyne activators, including PtCl2, Zn(OTf)2, AuCl, and AuCl3.
RESUMO
[reaction: see text] Treatment of 1-(2'-iodoethynylphenyl)-2-propyloxirane (3) with TpRuPPh(3)(CH(3)CN)(2)PF(6) catalyst (10 mol %) produced 1-iodo-2-naphthol (3a) exclusively in DMF, but gave 2-iodobenzo[d]oxepin (3b) efficiently in benzene. Such a solvent-dependent chemoselectivity suggests a solution equilibrium between ruthenium-pi-iodoalkyne and ruthenium-2-iodovinylidene intermediates.
RESUMO
Treatment of (o-ethynyl)phenyl epoxides with TpRuPPh(3)(CH(3)CN)(2)PF(6) (10 mol %) in hot toluene (100 degrees C, 3-6 h) gave 2-naphthols or 1-alkylidene-2-indanones very selectively with isolated yields exceeding 72%, depending on the nature of the epoxide substituents. Surprisingly, the reaction intermediate proved to be a ruthenium-pi-ketene species that can be trapped efficiently by alcohol to give an ester compound. This phenomenon indicates a novel oxygen transfer from epoxide to its terminal alkyne catalyzed by a ruthenium complex. A plausible mechanism is proposed on the basis of reaction products and the deuterium-labeling experiment. The 2-naphthol products are thought to derive from 6-endo-dig cyclization of (o-alkenyl)phenyl ketene intermediates, whereas 1-alkylidene-2-indanones are given from the 5-endo-dig cyclization pathway.