RESUMO
Quinones were firstly used as dipolarophiles in a photoclick 1,3-cycloaddition with 2,5-diaryltetrazoles, as photoactivatable predipoles, providing a novel and efficient access to three types of pyrazole-fused quinones (indazoledione derivatives). Distinctive features of this protocol include the use of light as the unique reagent and readily available, stable, and easy to handle starting materials and good to excellent yields. Photophysical and electrochemical properties of the quinones and their potential application as photoredox catalysts are also detailed.
RESUMO
An enantiopure helical ferrocene ( Rp)-5 with five ortho-condensed aromatic rings was synthesized using a PtCl2-catalyzed cycloisomerization of planar-chiral 2-ethynyl-1-(4-phenanthrenyl)ferrocene ( Rp)-6f, prepared in 3 steps from known enantiopure sulfinyl ferrocenyl boronic acid ( SS, Sp)-7, as the source of planar chirality. This pentacyclic helical ferrocene showed a very high optical rotation value and strong circular dichroism (CD) signals.
RESUMO
Angular tetracyclic p-peroxyquinols, p-quinols, and a pentacyclic double peroxide, showing anticancer properties, were synthesized from the corresponding phenols by an environmentally friendly solvent- and wavelength-controlled irradiation under air in the absence of an external photosensitizer.
RESUMO
A new family of homochiral silver complexes based on carbophilic interactions with ortho-phenylene ethynylene (o-OPE) scaffolds containing up to two silver atoms are described. These compounds represent a unique class of complexes with chirality at the metal. Chiral induction is based on the inclusion of chiral sulfoxides, which allow efficient transfer of chirality to the helically folded o-OPE, leading to circularly polarized luminescence (CPL)- and vibrational circular dichroism (VCD)-active compounds. In the presence of silver(I) cations, carbophilic interactions dominate, which promote helical structures with a defined helicity. This is one of the very scarce examples of the use of such interactions in the attractive field of abiotic foldamers. The switching event has been extensively studied by using different chiroptical techniques, including circular dichroism, CPL, and VCD, and represents one of the few CPL switches described in the literature.
RESUMO
A general synthetic route to γ-oxo alkyl or α-hydroxy benzyl 2-substituted benzoquinones has been developed through a one-pot Rh-catalyzed C-C bond formation/oxidative demethylation sequence from 2,5-dimethoxy aryl boronic acids and several electron deficient alkenes or aldehydes. The process allows rapid access to functionalized benzoquinones under very mild conditions and good yields. We disclose the first example of a Rh-catalyzed 1,4-addition reaction of benzoquinonyl boronic acid to methyl vinyl ketone and other conjugate acceptors, which allows the direct synthesis of 2-(γ-functionalized alkyl) substituted benzoquinones.
RESUMO
Lewis acid catalyzed Friedel-Crafts alkylation of indoles has been achieved in high yields and selectivities using p-quinols as electrophiles. (S)-Binol-3,3'-(9-anthracenyl)-phosphoric acid was able to catalyze the enantioselective formation of 5-(3-indole)-2-cyclohexenone derivatives. Experimental results and theoretical calculations explained the enantioselectivity based on a transition state where two water molecules act as a tether joining the p-quinol with the phosphoric acid and the NH of indole, thus facilitating the desymmetrization of the prochiral cyclohexadienone framework.
RESUMO
ortho-Oligo(phenylene)ethynylenes (o-OPEs) stapled with enantiopure 2,3-dihydroxybutane diethers have highly intense circular dichroism (CD) spectra and excellent circular polarized luminescence (CPL) responses (glum values up to 1.1 × 10-2), which are consistent with homochiral helically folded structures. In the presence of Ag(i), a change in the CPL emission is observed, representing the first example of CPL active small organic molecular emitters, which can be modulated by carbophilic interactions in a reversible manner.
RESUMO
Four stereoisomers of sulfinyl ferrocenyl-substituted helicenequinones having central, planar, and helical elements of chirality were stereoselectively formed, in one step, from reaction between enantiopure sulfinyl ferrocenyl dienes and a sulfinyl quinone. Asymmetric synthesis, kinetic resolution, or chemical resolution processes occurred in sequential cycloaddition, sulfoxide elimination, and partial aromatization steps.
RESUMO
Indole substituted twistane-like derivatives resulted in a reaction between 3,5-dimethyl-2-quinonyl boronic acid and 2-alkenyl indoles. Their MCPBA oxidation gave 6/6/9 caged systems. Boronic acid acts as a temporal promoter allowing a site-selective conjugate addition of the heteroaromatic system to the methyl substituted C-3 quinone carbon, giving an intermediate diene which is regioselectively trapped by intramolecular [4 + 2] cycloaddition.
RESUMO
Up to six differently substituted highly challenging angularly-oxygenated tricyclic core models of natural angucyclinones were stereoselectively synthesized from a common p-quinol intermediate obtained from Oxone-mediated oxidative dearomatization of the corresponding tricyclic phenol.
Assuntos
Antraquinonas/química , Fenóis/química , Ácidos Sulfúricos/química , Hidroquinonas/química , OxirreduçãoRESUMO
A new class of enantiopure ortho,ortho-disubstituted azobenzene photoswitches has been synthesized from (S)-2-(p-tolylsulfinyl)benzoquinone and arylhydrazines. The sulfoxide acts as a unidirectional controller of the helical chirality that arises in the Zâ isomer after photoisomerization. Highly congested E-azobenzenes 5 c showed two atropisomeric diastereoconformers in the solid state that converged upon irradiation into a unique Zâ isomer with defined helicity (M), as evident in the X-ray structure. The chiroptical properties of this three-state enantiopure switch can be externally tuned both photochemically and/or thermally. Theoretical CD spectra calculated by using time-dependent DFT methods support the existence of two atropoisomeric Eâ isomers and only one Zâ isomer with (M) helicity. Complementary to the classical azobenzene-based switches, the photoswiching event is promoted under green/blue light and do not occur under UV irradiation.
RESUMO
A convergent approach based on Diels-Alder reactions between polycyclic dienes and benzoquinones has emerged as a powerful tool for the construction of helicenequinones and bisquinones. Chemical resolution and asymmetric Diels-Alder reactions with sulfinyl quinones provide direct access to enantiopure derivatives. Biaryl or ferrocenyl dienes can be resolved leading to helicenequinones having additional axial or planar chirality.
RESUMO
Cochinchinenone has been synthesized in only five steps and four pots and in 58% overall yield from commercially available 2,3-dimethoxy-4-hydroxy-benzaldehyde and OPMB-protected p-hydroxy acetophenone, the key step being the oxone-mediated oxidative dearomatization of the corresponding ketone-containing p-substituted phenol.
Assuntos
Antibacterianos/síntese química , Produtos Biológicos/síntese química , Chalconas/síntese química , Antibacterianos/química , Antibacterianos/isolamento & purificação , Antibacterianos/farmacologia , Produtos Biológicos/química , Produtos Biológicos/isolamento & purificação , Produtos Biológicos/farmacologia , Catálise , Chalconas/química , Chalconas/isolamento & purificação , Chalconas/farmacologia , Helicobacter pylori/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Estrutura Molecular , Ressonância Magnética Nuclear BiomolecularRESUMO
Spring loaded: the smallest members of a family of carbon nanocoils (CNCs), adopting a fixed helical structure, have been synthesized by introduction of one or two staples in o-phenylene ethynylene oligomers. The chiroptical responses of the systems having enantiopure L-tartrate-derived staples confirmed the induced helicity. Theoretical studies suggest that these CNCs are pseudoelastic.
RESUMO
Both enantiomers of ferrocene [4]-helicenequinone 6, showing planar and helical chiralities, have been synthesized with very high optical purities using, as the key step, a kinetic resolution process between planar-chiral racemic ferrocene diene 2 and enantiopure sulfinyl benzoquinone (S)-3.
RESUMO
Good to excellent stereoselectivities were achieved in the reductive cyclization (with Et(3)SiH/trimethylsilyl trifluoromethanesulfonate (TMSOTf)) of enantiopure hydroxy sulfinyl ketones en route to 2,5-cis-disubstituted tetrahydrofuran skeletons. Electrostatic effects of the exocyclic sulfoxide, which stabilized the reactive intermediate oxocarbenium conformations, were responsible for the observed stereocontrol. A model is proposed to explain the results. The use of this reaction and the asymmetric ß-ketosulfoxide reduction as key steps facilitated the total enantioselective synthesis of the natural ß-C-aryl glycoside (+)-goniothalesdiol.
Assuntos
Produtos Biológicos/química , Furanos/química , Metano/análogos & derivados , Sulfóxidos/química , Ciclização , Furanos/síntese química , Espectroscopia de Ressonância Magnética , Metano/química , Conformação Molecular , Estrutura Molecular , EstereoisomerismoRESUMO
Reactions of heteroaromatic compounds with 3-methyl substituted 2-quinonyl boronic acids proceeded by 1,4-addition followed by spontaneous protodeboronation, leading directly to the Friedel-Crafts alkylation products instead of the commonly observed alkenylation derivatives resulting from quinones. The boronic acid acts as a temporary regiocontroller, making the system a highly reactive quinone equivalent and opening a direct access to 5,5-disubstituted cyclohexene-1,4-diones.
RESUMO
The synthesis of the C15-C26 fragment of (-)-dictyostatin is reported in 10 steps and 28% overall yield. The key steps are the two stereoselective sulfoxide-directed processes: a Reformatsky-type reaction and a ß-keto sulfoxide reduction.
Assuntos
Antineoplásicos/síntese química , Macrolídeos/síntese química , Estrutura Molecular , EstereoisomerismoRESUMO
The synthesis and anodic oxidation of a variety of 2,5-diaryl or dialkynylaryl substituted 1,4-dialkoxybenzenes to quinone bisketals is described. The study of the X-ray structures and electrochemical and spectroscopic properties evidenced that these pairs constitute a first approach to the concept of a molecular nanofuse.
RESUMO
Substituted 2-quinonyl boronic acids have been synthesised from 1,4-dimethoxy aromatic derivatives in two steps: regiocontrolled boronation and oxidative demethylation. The study of their dienophilic behaviour evidenced that the boron substituent significantly increases the reactivity and triggers an efficient domino process in which the Diels-Alder reaction was followed by a protodeboronation or dehydroboronation, depending on the substitution on both the quinone and diene partners. The boronic acid acts as a temporary controller, opening a direct access to trans-fused meta-regiosomeric adducts when 3-methyl-substituted 2-quinonyl boronic acids react with dienes with a substituent at C-1. A particularly valuable synthetic result was obtained in the reaction between 3,6-dimethyl-2-quinonyl boronic acid and piperylene under an oxygen atmosphere; trans-fused 8a-hydroxy-2,4a,8-trimethyl tetrahydronaphthoquinone was formed directly, in excellent yield and in a highly diastereoselective manner.