Indirect electrochemical cyclization of bromoalkoxylated derivatives mediated by nickel(II) complex in environmentally friendly medium

An improved procedure has been developed using a catalytic amount of a nickel(II) complex in the efficient and selective electrochemical cyclization of propargyloxy and allyloxy bromo derivatives into substituted tetrahydrofurans using ethanol and ethanol–water mixtures as environmental-friendly systems. The reduction of the substrates proceeded via one-electron cleavage of the carbon–bromine bond to form a radical-type intermediate that undergoes cyclization to afford the tetrahydrofuran structures in good yields.Fundação para a Ciência e a Tecnologia (FCT

Indirect electrochemical cyclisation of bromoalkoxylated derivatives using environmentally friendly methodologies

The electrochemical intramolecular cyclization of bromoalkoxylated derivatives 1 using Ni(II) complex as mediator of electron transfer was carried out in ethanol by constant-current electrolysis in one-compartment cell in the absence of sacrificial anodes as an environmentally friendly systems. It is demonstrated that the electroreduction reaction of bromoalkoxylated derivatives was catalyzed by the electrogenerated Ni(I) complexes. Only cyclization to the five-membered-ring esters was obtained in moderate to good yields as the main products. Functionalyzed tetrahydrofurans are important intermediates in the synthesis of natural products such as lignans. A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and constant-current electrolysis.Fundação para a Ciência e a Tecnologia (FCT

Electrochemical catalytic cyclization reactions using environmentally friendly methodologies

The electrochemical intramolecular cyclisation of bromoalkoxylated derivatives 1 was carried out using Ni(II) complexes as the catalysts in ethanol solutions by constant-current electrolysis in one-compartment cell in the absence of sacrificial anodes as an environmentally friendly system. The reduction of the substrates proceeds via one-electron cleavage of the carbon–bromine bond to form radical-type intermediates that undergo cyclisation to afford cyclic ethers in moderate to good yields.Fundação para a Ciência e a Tecnologia (FCT

Electroreductive intramolecular cyclization of bromoalkoxylated derivatives catalyzed by nickel(I) tetramethylcyclam in "green" media

The (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes is shown to be an effective catalyst for the intramolecular radical-type cyclisation of bromoalkoxylated derivatives 1 in alcohol and / or alcohol/water mixtures as well as in microemulsions made with cationic and anionic surfactants. The results obtained indicate that the reaction proceeds via cleavage of the carbon–bromine bond to form a radicaltype intermediate that undergoes cyclisation on the unsaturated C-C bond to afford substituted tetrahydrofurans. The reactions are more selective and take place at higher current density than when carried out in conventional aprotic solvents

Synthesis of heterocyclic compounds by radical electrochemical approach in environmentally friendly media

Radical cyclisation is rapidly becoming an important method for the formation of cyclic systems. Hence, some electrochemical results obtained in the study of electroreductive intramolecular cyclisation of ethyl 2-bromo-3-(3,4-methylenedioxophenyl)-3-(propargyloxy)propanoate (1a), [1-bromo-2-methoxy-2-(prop-2’-ynyloxy) ethyl] benzene (1b) and 1-[2-bromo-2-phenyl-1-(prop-2’-ynyloxy)ethyl]-4-methoxybenzene (1c) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in ethanol, ethanol / water and microemulsions made with cationic and anionic surfactants are presented. The results obtained indicate that the reaction proceeds via cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization on the unsaturated C-C bond to afford the substituted tetrahydrofurans.Fundação para a Ciência e a Tecnologia (FCT

Electrochemical study of nickel(salen) and cobalt(salen) derivatives complexes in the presence of unsaturated halides

The electrochemical intramolecular cyclisation of allyl 2-bromophenyl ethers in N,N'-dimethylformamide at constant current in a diaphragmless cell has been developed using Ni(II) and Co(II) complexes as electron-transfer mediators. Cyclic compounds are obtained in good yields under appropriate experimental conditions

Electrosynthesis of nitrogen heterocycles using environmentally friendly methodologies

Cyclic voltammetry and constant-current electrolysis in a one-compartment cell with a sacrificial anode has been used to study the indirect electroreduction of N-allyl- -haloamides by electrogenerated Ni(I) complexes conducted inN,N-dimethylformamide (DMF) and acetonitrile (ACN) and the resultswere compared with those obtained in protic solvents such as EtOH and EtOH–H2O mixtures. It was observed that the indirect electrochemical reduction of N-allyl- -haloamides led to the corresponding lactams and the yields and selectivities obtained in EtOH and EtOH–H2O were much better than those obtained in DMF or ACN.Fundação para a Ciência e a Tecnologia (FCT

Gamma-Secretase-Dependent and -Independent Effects of Presenilin1 on β-Catenin·Tcf-4 Transcriptional Activity

Presenilin1 (PS1) is a component of the γ-secretase complex mutated in cases of Familial Alzheimer's disease (FAD). PS1 is synthesized as a 50 kDa peptide subsequently processed to two 29 and 20 kDa subunits that remain associated. Processing of PS1 is inhibited by several mutations detected in FAD patients. PS1 acts as negative modulator of β-catenin·Tcf-4 transcriptional activity. In this article we show that in murine embryonic fibroblasts (MEFs) the mechanisms of action of the processed and non-processed forms of PS1 on β-catenin·Tcf-4 transcription are different. Whereas non-processed PS1 inhibits β-catenin·Tcf-4 activity through a mechanism independent of γ-secretase and associated with the interaction of this protein with plakoglobin and Tcf-4, the effect of processed PS1 is prevented by γ-secretase inhibitors, and requires its interaction with E- or N-cadherin and the generation of cytosolic terminal fragments of these two cadherins, which in turn destabilize the β-catenin transcriptional cofactor CBP. Accordingly, the two forms of PS1 interact differently with E-cadherin or β-catenin and plakoglobin: whereas processed PS1 binds E-cadherin with high affinity and β-catenin or plakoglobin weakly, the non-processed form behaves inversely. Moreover, contrarily to processed PS1, that decreases the levels of c-fos RNA, non-processed PS1 inhibits the expression c-myc, a known target of β-catenin·Tcf-4, and does not block the activity of other transcriptional factors requiring CBP. These results indicate that prevention of PS1 processing in FAD affects the mechanism of repression of the transcriptional activity dependent on β-catenin

Electrochemical cyclizations of organic halides catalyzed by electrogenerated nickel(I) complexes: towards environmentally friendly methodologies

This review concentrates on the intramolecular cyclizations of organic halides catalyzed by nickel complexes using an electrochemical methodology, as an alternative to the classical radical or transitionmetal catalyzed or mediated processes.info:eu-repo/semantics/publishedVersio