RESUMO
Allenylzinc formed via oxygen-promoted zinc/iodine exchange between propargyl iodides and diethylzinc can be trapped by intramolecular reaction with various electrophiles such as aldehydes, ketones, esters, carbamates, and imides. Potentially useful building blocks were obtained in high yields.
RESUMO
Propargyl iodides are good precursors for allenylzincs via reaction with diethylzinc, even in nondegassed medium. These reactions proceed via zinc/iodine exchange. Owing to the previously reported detection of propargyl radical by ESR experiments, in this process a radical mechanism was suspected. Calculations of the C-Zn BDEs in allenyl- and propargylzinc species were performed with the CBS-QB3 method to demonstrate that propargyl radicals could undergo homolytic substitution at zinc. The stabilization of allenylzinc derivatives by chelation, made possible by the selection of appropriate ortho-substituted 3-phenylalkynyl iodides as precursors, was shown to influence the regioselectivity of their addition to aldehydes and ketones. The more stabilized the chelated allenylzinc intermediate, the higher the ratio of homopropargylic alcohols.
RESUMO
The production of propargyl radicals in the reaction of dialkylzincs with propargyl iodides in nondegassed medium was investigated by EPR using tri-tert-butylnitrosobenzene (TTBNB) as a spin trap. The radical mechanism and the nature of the observed species were confirmed by the trapping of propargyl radicals generated by an alternative pathway: i.e., upon irradiation of propargyl iodides in the presence of hexa-n-butyldistannane. In dialkylzinc-mediated experiments a high concentration of adduct was instantaneously observed, whereas no spontaneous production of spin adduct was detected in a blank experiment performed with the propargylic iodide and TTBNB in the absence of diethylzinc. Under irradiation in the presence of distannane, two different species were observed at the very beginning of the irradiation; the nitroxide resulting from the trapping of propargyl radical at the propargyl carbon remained the only species detected after irradiating for several minutes. The absence of adducts resulting from the trapping of allenyl canonical forms was supported by DFT calculations and by the preparation of an authentic sample.
Assuntos
Alcinos/química , Hidrocarbonetos Iodados/química , Iodo/química , Compostos Organometálicos/química , Zinco/química , Espectroscopia de Ressonância de Spin Eletrônica , Radicais Livres/química , Estrutura Molecular , Teoria QuânticaRESUMO
CuO nanoparticles have been studied for C-N, C-O, and C-S bond formations via cross-coupling reactions of nitrogen, oxygen, and sulfur nucleophiles with aryl halides. Amides, amines, imidazoles, phenols, alcohols and thiols undergo reactions with aryl iodides in the presence of a base such as KOH, Cs(2)CO(3), and K(2)CO(3) at moderate temperature. The procedure is simple, general, ligand-free, and efficient to afford the cross-coupled products in high yield.
Assuntos
Cobre/química , Hidrocarbonetos Iodados/química , Nanopartículas/química , Compostos de Sulfidrila/química , Álcoois/química , Amidas/química , Aminas/química , Catálise , Imidazóis/química , Estrutura Molecular , Tamanho da Partícula , Fenóis/química , Estereoisomerismo , Propriedades de SuperfícieRESUMO
Simple addition: Copper(II) aqua complex 1 can be prepared in a one-pot synthesis and is self-assembled by H-bond interactions. Complex 1 is shown to accelerate the nitroaldol reaction on water, which is a heterogeneous process, requiring no additive or base, and 1 can be recycled without loss of activity. Copper(II) aqua complex 1 has been prepared in a one-pot synthesis. The single crystal X-ray analysis showed that the complex is self-assembled through aqua ligands by H-bond interactions and the copper(II) atoms are pentacoordinated with square pyramidal geometry. Complex 1 has been studied for the acceleration of the nitroalodol reaction on water. It is a clean technological process and the catalyst can be recycled without loss of activity.
RESUMO
Chiral copper(II) coordination polymers 1a-c have been prepared by one-pot synthesis in high yield. Their single-crystal X-ray analysis showed that repeating units are connected to each other by carboxylate linker and copper(II) atoms are pentacoordinated with distorted square-pyramidal geometry for 1a-b and square-planar geometry for 1c. These polymers have catalyzed the kinetic resolution of secondary alcohols by acylation with up to 90% ee ( s = 50).
RESUMO
CuO nanoparticles catalyze the C-N cross coupling of amines with iodobenzene in excellent yields. The reaction is simple and efficient and operates under air with ligand free conditions. The catalyst is recyclable without loss of activity.