Electroreductive Intramolecular Cyclization of a Bromo Propargyloxy Ester Catalyzed by Nickel(I) Tetramethylcyclam Electrogenerated at Carbon Cathodes in Dimethylformamide

Esteves, Ana Paula; Goken, Danielle M.; Klein, Lee J.; Lemos, M.A.N.D.A.; Medeiros, Maria José; Peters, Dennis G.

doi:10.1021/jo026102k

Cited by 55 publications

(75 citation statements)

References 52 publications

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“…To augment the arguments presented above, it is instructive to consider another project 14 in our laboratory that entailed the catalytic reduction of a bromopropargyloxy ester (7) by electrogenerated nickel(I) tetramethylcyclam (8) in dimethylformamide (DMF) containing tetraethylammonium tetrafluoroborate (TEABF 4 ).…”

Section: Choosing a Procatalystmentioning

confidence: 99%

Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen

2016

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Catalytic reduction of halogenated organic compounds by electrogenerated nickel(I) complexes first appeared in the literature as a series of publications [1][2][3][4][5] from the laboratory of Derek Pletcher. In this early work, a family of nickel(II) procatalysts (or catalyst precursors) was employed, which included the compound [[2,2′-[1,2-ethanediylbis-(nitrilomethylidyne)]bis [phenolato]]-N,N′,O,O′]nickel(II), hereafter called nickel(II) salen (1). At a variety of cathodes (mercury, glassy carbon, platinum, and gold) and in numerous non-aqueous solventelectrolyte media [for example, dimethylformamide containing tetran-butylammonium tetrafluoroborate (DMF-TBABF 4 ) or acetonitrile containing tetramethylammonium perchlorate (CH 3 CN-TMAP)], chocolate-brown nickel(II) salen (1) undergoes a reversible, metalcentered, one-electron reduction to green nickel(I) salen (2). On the basis of density functional theory, it was established later 6 that reduction of nickel(II) salen can also produce a ligand-reduced form (3) of the parent complex in which a single electron is added to the carbon atom of one imino (C=N) bond of the ligand:Furthermore, the energy of 3 was calculated to be approximately only 2-3 kcal mol -1 higher than that of 2, meaning that both reduced states of 1 are accessible electrochemically-which becomes vitally important in later discussion.Shown in Fig. 1 is a cyclic voltammogram, recorded at 100 mV s -1 on a glassy carbon electrode in dimethylformamide containing tetramethylammonium tetrafluoroborate (TMABF 4 ) as the supporting electrolyte, which reveals the reversible one-electron reduction of nickel(II) salen. For the experimental conditions employed, the cathodic and anodic peak potentials (E pc and E pa ) are -0.95 and -0.84 V, respectively, and the cathodic and anodic peak currrents (I pc and I pa ) are identical. What is not seen in Fig. 1 (and what must be avoided) is that, at more negative potentials, another prominent cathodic peak is observed, due to the fact that the salen ligand itself can undergo further and irreversible degradation-which destroys the desired catalytic ability of 2. Our First Use of Electrogenerated Nickel(I) SalenOur first published effort to employ nickel(I) salen (2), electrogenerated at a reticulated vitreous carbon cathode in dimethylformamide-tetraethylammonium perchlorate (DMF-TEAP), was as a catalyst for the reductive intramolecular cyclizations of two acetylenic halides-namely, 6-bromo-1-phenyl-1-hexyne (4) and 6-iodo-1-phenyl-1-hexyne (5) Our goals were: (a) to overcome problems associated with direct reduction of these two compounds at mercury pool or reticulated vitreous carbon electrodes; and (b) to maximize the yield of the desired product (benzylidenecyclopentane, 6). Earlier, when these two acetylenic halides were reduced directly at a mercury pool cathode, 8 more than seven different products were obtained, and 6 was obtained in a yield below 25%. Then, in a subsequent investigation of the direct reduction of 6-iodo-1-phenyl-1-hexyne at a reticulated...

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Section: Choosing a Procatalystmentioning

confidence: 99%

Catalytic Reduction of Organic Halides by Electrogenerated Nickel(I) Salen

2016

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“…• C and the solution was stirred for an additional 1 h. Saturated aqueous ammonium chloride solution was added to quench the reaction and the mixture was extracted with ethyl acetate, after which the organic phase was washed three times with brine, dried over anhydrous sodium sulfate, concentrated under reduced pressure, and introduced into a silica-gel chromatographic column which was eluted with 20:1 hexane:ethyl acetate to afford the desired product as a colorless oil: 1 Figure 1 is a cyclic voltammogram recorded at 100 mV s −1 for the direct reduction of a 2.0 mM solution of 1 at a silver cathode (curve A, solid line) in oxygen-free DMF containing 0.10 M tetraethylammonium tetrafluoroborate (TEABF 4 ). For comparison, a cyclic voltammogram for reduction of 1 at a glassy carbon electrode under the same conditions is included in this figure (curve B, dashed line).…”

Section: Synthesis Of Ethyl Trans-3-(3 4 -Dimethoxyphenyl)acrylate (mentioning

confidence: 99%

“…Thus, when a proton donor is introduced, no 7 is formed, but 8 (a species undetected in experiments performed in the absence of a proton donor) is produced. (1).-Scheme 1 Scheme 1. Proposed mechanistic steps for direct electrochemical reduction of bromo propargyloxy ester 1 at a silver cathode.…”

Section: Controlled-potential Electrolysis Of Ethyl 2-bromo-3-(3 4 -mentioning

confidence: 99%

“…In the first of those investigations, 1 we examined the reductive intramolecular cyclization of ethyl 2-bromo-3-(3 ,4 -dimethoxyphenyl)-3-(propargyloxy)propanoate (1), catalyzed by electrogenerated nickel(I) tetramethylcyclam, to afford 2-(3 ,4 -dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methylenetetrahydrofuran (2) in good yield (72-85%); the latter species is a desired precursor for the formation of isogmelinol (a furofuran lignan). In addition, a second product, 2-(3 ,4 -dimethoxyphenyl)-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3), was obtained in significant yield (22-30%).…”

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Electrochemical Reduction of a Bromo Propargyloxy Ester at Silver Cathodes in Dimethylformamide

Henderson

Buehler

Pasciak

et al. 2014

J. Electrochem. Soc.

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Cyclic voltammograms for the reduction of ethyl 2-bromo-3-(3 ,4 -dimethoxyphenyl)-3-(propargyloxy)propanoate (1) at a silver cathode in dimethylformamide (DMF) containing 0.10 M tetraethylammonium tetrafluoroborate (TEABF 4 ) exhibit several cathodic peaks, the first of which is attributed to reductive cleavage of the carbon-bromine bond. Controlled-potential (bulk) electrolyses of 1 at silver gauze electrodes in DMF-0.10 M TEABF 4 give rise to four products: cis-and trans-isomers of ethyl 3-(3 ,4 -dimethoxyphenyl)-prop-2-enoate (4), ethyl 3-(3 ,4 -dimethoxyphenyl)propiolate (7), and ethyl 3-(3 ,4 -dimethoxyphenyl)-3-(prop-2-yn-1-yloxy)propanoate (8). These products have been identified with the aid of mass spectrometry and nuclear magnetic resonance spectroscopy. We propose that reduction of 1 involves two-electron cleavage of the carbon-bromine bond to form a carbanion. Then the latter species eliminates − OCH 2 C≡CH to afford 4. In addition, − OCH 2 C≡CH can deprotonate 1 to yield (Z)-ethyl 2-bromo-3-(3 ,4 -dimethoxyphenyl)acrylate (5), which is further deprotonated by − OCH 2 C≡CH to give 7. Alternatively, the carbanion resulting from the original two-electron reduction of 1 can gain a proton from the medium to form 8. In two previous projects 1,2 involving collaboration with our laboratory, electrochemical methods were probed as an avenue to the synthesis of building blocks for lignans, which comprise a class of phenylalanine-derived compounds that have attracted considerable attention due to their pharmacological activity and abundance in nature. In the first of those investigations, 1 we examined the reductive intramolecular cyclization of ethyl 2-bromo-3-(3 ,4 -dimethoxyphenyl)-3-(propargyloxy)propanoate (1), catalyzed by electrogenerated nickel(I) tetramethylcyclam, to afford 2-(3 ,4 -dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methylenetetrahydrofuran (2) in good yield (72-85%); the latter species is a desired precursor for the formation of isogmelinol (a furofuran lignan). In addition, a second product, 2-(3 ,4 -dimethoxyphenyl)-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3), was obtained in significant yield (22-30%).A second paper 2 was concerned with the direct reduction of 1 at both glassy carbon and reticulated vitreous carbon cathodes in dimethylformamide (DMF) containing various tetraalkylammonium salts. Interestingly, although 2 was not obtained, 3 (which * Electrochemical Society Student Member.* * Electrochemical Society Fellow. z E-mail: peters@indiana.edu arises via base-promoted rearrangement of 2) was found in modest yield (18-26%). More importantly, the principal product was ethyl trans-3-(3 ,4 -dimethoxyphenyl)acrylate (4), although small amounts of (Z)-ethyl 2-bromo-3-(3 ,4 -dimethoxyphenyl)acrylate (5) and ethyl 3-(3 ,4 -dimethoxyphenyl)-2,3-bis(prop-2-yn-1-yloxy)propanoate (6) were detected.Recent publications from our laboratory 3-8 and by other research groups 9-24 have dealt with the electrochemistry of halogenated organic compounds at silver cathodes and have revealed the catalytic ef...

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“…6 Schiff base macrocycles containing two bridging phenol groups have been widely used to synthesize homo-and hetero-multinuclear transition metal complexes. 7 Most investigations of these 3d-metal ion complexes are an outgrowth of stereoselective catalysts in reactions such as alkene epoxidation, 8 epoxide carboxylation, 9 intramolecular reductive cyclization, 10 electrochemical annulation, 11 and oxidation of hydrocarbons. 12 All of these processes can potentially generate stereogenic centers, thus the chiral macrocycles, which can induce chirality, are of great interest.…”

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confidence: 99%