Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 7 de 7
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Am Chem Soc ; 143(44): 18548-18558, 2021 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-34709810

RESUMO

Covalent assemblies of conjugated organic chromophores provide the opportunity to engineer new excited states with novel properties. In this work, a newly developed triple-stranded cage architecture, in which meta-substituted aromatic caps serve as covalent linking groups that attach to both top and bottom of the conjugated molecule walls, is used to tune the properties of thiophene oligomer assemblies. Benzene-capped and triazine-capped 5,5'-(2,2-bithiophene)-containing arylene cages are synthesized and characterized using steady-state and time-resolved spectroscopic methods. The conformational freedom and electronic states are analyzed using time-dependent density functional theory. The benzene cap acts as a passive spacer whose electronic states do not mix with those of the chromophore walls. The excited state properties are dominated by through-space interactions between the chromophore subunits, generating a neutral Frenkel H-type exciton state. This excitonic state undergoes intersystem crossing on a 200 ps time scale while the fluorescence output is suppressed by a factor of 2 due to a decreased radiative rate. Switching to a triazine cap enables electron transfer from the chromophore-linker after the initial excitation to the exciton state, leading to the formation of a charge-transfer state within 10 ps. This state can avoid intersystem crossing and exhibits red-shifted fluorescence with enhanced quantum yield. The ability to interchange structural modules with different electronic properties while retaining the overall cage morphology provides a new approach for tuning the properties of discrete chromophore assemblies.

2.
Chemistry ; 27(15): 4898-4902, 2021 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-33576516

RESUMO

Ruthenium-catalyzed butadiene-mediated benzannulation enabled the first synthesis of 3,10-(di-tert-butyl)rubicene and its N-doped derivatives as well as preliminary studies on their photophysical properties. Unlike the parent rubicene and 3,10-(di-tert-butyl)rubicene, which adopt classical herringbone-type packing motifs in the solid state, the N-doped congener 7 b displayed columnar packing with an alternating co-facial arrangement of aromatic and heteroaromatic substructures.

3.
Chem Rev ; 121(7): 4045-4083, 2021 04 14.
Artigo em Inglês | MEDLINE | ID: mdl-33576620

RESUMO

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.


Assuntos
Compostos Heterocíclicos/síntese química , Compostos Organometálicos/química , Compostos Policíclicos/síntese química , Rutênio/química , Catálise , Ciclização , Oxirredução , Processos Fotoquímicos , Estereoisomerismo
4.
Chemistry ; 25(54): 12517-12520, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31403727

RESUMO

Direct conversion of aldehydes to ketones is achieved via rhodium-catalyzed vinyl triflate-aldehyde reductive coupling-redox isomerization mediated by potassium formate. This method circumvents premetalated C-nucleophiles and discrete redox manipulations typically required to form ketones from aldehydes.

5.
J Am Chem Soc ; 141(17): 6864-6868, 2019 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-30998328

RESUMO

A regiodivergent catalytic method for direct conversion of aldehydes to branched or linear alkyl ketones is described. Rhodium complexes modified by P tBu2Me catalyze formate-mediated aldehyde-vinyl bromide reductive coupling-redox isomerization to form branched ketones. Use of the less strongly coordinating ligand, PPh3, promotes vinyl- to allylrhodium isomerization en route to linear ketones. This method bypasses the 3-step sequence often used to convert aldehydes to ketones involving the addition of pre-metalated reagents to Weinreb or morpholine amides.


Assuntos
Aldeídos/química , Complexos de Coordenação/química , Formiatos/química , Cetonas/síntese química , Ródio/química , Compostos de Vinila/química , Catálise , Isomerismo , Oxirredução
6.
Org Lett ; 19(18): 4790-4793, 2017 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-28841323

RESUMO

Dioxiranes are among the most selective and useful reagents for C(sp3)-H hydroxylation, but the development of a general dioxirane-mediated catalytic method has been an elusive goal. A trifluoromethyl ketone catalyst in combination with Oxone is shown to enable the first dioxirane-mediated catalytic hydroxylations that approximate the reactivity and selectivity of isolated dioxiranes. The mild reaction conditions allow for selective 3° hydroxylation and 2° oxidation and are tolerant of acid-sensitive functionality and electron-neutral arenes.

7.
Org Lett ; 18(15): 3826-9, 2016 08 05.
Artigo em Inglês | MEDLINE | ID: mdl-27391543

RESUMO

The first examples of catalysis of aliphatic C-H hydroxylation by an iminium salt are presented. The method allows the selective organocatalytic hydroxylation of unactivated 3° C-H bonds at room temperature using hydrogen peroxide as the terminal oxidant. Hydroxylation of an unactivated 2° C-H bond is also demonstrated. Furthermore, improved functional group compatibility over other catalytic methods is reported in the form of selectivity for aliphatic C-H hydroxylation over alcohol oxidation. On the basis of initial mechanistic studies, an oxaziridinium species is proposed as the active oxidant.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...