- On the role of samarium/HMPA in the post electron-transfer steps in Sml2 reductions
-
The reaction of p,p-dichlorobenzophenone with Sml2 was studied in the presence of variable amounts of HMPA. The electron-transfer step takes place instantaneously. In the presence of excess substrate, the addition of HMPA retarded the rate of c
- Farran, Hani,Hoz, Shmaryahu
-
-
Read Online
- A convenient pinacol coupling of diaryl ketones with B2pin2viapyridine catalysis
-
A convenient, pyridine-boryl radical-mediated pinacol coupling of diaryl ketones is developed. In contrast to the conventional pinacol coupling that requires sensitive reducing metal, the current method employs a stable diboron reagent and pyridine Lewis base catalyst for the generation of a ketyl radical. The newly developed process is operationally simple, and the desired diols are produced with excellent efficiency in up to 99% yield within 1 hour. The superior reactivity of diaryl ketone was observed over monoaryl carbonyl compounds and analyzed by DFT calculations, which suggests the necessity of both aromatic rings for the maximum stabilization of the transition states.
- Jo, Junhyuk,Kim, Seonyul,Choi, Jun-Ho,Chung, Won-Jin
-
supporting information
p. 1360 - 1363
(2021/02/22)
-
- Visible Light Induced Reduction and Pinacol Coupling of Aldehydes and Ketones Catalyzed by Core/Shell Quantum Dots
-
We present an efficient and versatile visible light-driven methodology to transform aryl aldehydes and ketones chemoselectively either to alcohols or to pinacol products with CdSe/CdS core/shell quantum dots as photocatalysts. Thiophenols were used as proton and hydrogen atom donors and as hole traps for the excited quantum dots (QDs) in these reactions. The two products can be switched from one to the other simply by changing the amount of thiophenol in the reaction system. The core/shell QD catalysts are highly efficient with a turn over number (TON) larger than 4 × 104 and 4 × 105 for the reduction to alcohol and pinacol formation, respectively, and are very stable so that they can be recycled for at least 10 times in the reactions without significant loss of catalytic activity. The additional advantages of this method include good functional group tolerance, mild reaction conditions, the allowance of selectively reducing aldehydes in the presence of ketones, and easiness for large scale reactions. Reaction mechanisms were studied by quenching experiments and a radical capture experiment, and the reasons for the switchover of the reaction pathways upon the change of reaction conditions are provided.
- Xi, Zi-Wei,Yang, Lei,Wang, Dan-Yan,Feng, Chuan-Wei,Qin, Yufeng,Shen, Yong-Miao,Pu, Chaodan,Peng, Xiaogang
-
p. 2474 - 2488
(2021/02/05)
-
- CBZ6 as a Recyclable Organic Photoreductant for Pinacol Coupling
-
A recyclable organic photoreductant (1 mol % CBZ6)-catalyzed reductive (pinacol) coupling of aldehydes, ketones, and imines has been developed. Irradiated by purple light (407 nm) using triethylamine as an electron donor, a variety of 1,2-diols and 1,2-diamines could be prepared. The oxidation potential of the excited state of CBZ6 is established as -1.92 V (vs saturated calomel electrode (SCE)). The relative high reductive potential enables the reductive coupling of carbonyl compounds and their derivatives. CBZ6 can be prepared in gram scale and is acid/base- or air-stable. It could be applied in large-scale photoreductive synthesis and recovered in high yield after the reaction.
- Wang, Hua,Qu, Jian-Ping,Kang, Yan-Biao
-
supporting information
p. 2900 - 2903
(2021/05/05)
-
- Enhanced catalytic activity of one-dimensional CdS @TiO2 core-shell nanocomposites for selective organic transformations under visible LED irradiation
-
In this study, we are interested in the photocatalytic activity under visible LED irradiation of one- dimensional (1D) CdS @TiO2 core–shell nanocomposites (CSNs) prepared through a facile and convenient method. For the synthesis of 1D CdS@TiO2 core/shell structure, titania source (Tetrabutyl titanate) was hydrolyzed by water vapor transmission on the surface of CdS nanowires (NWs) which were prepared via solvothermal method. The characterization of 1D CdS@TiO2 core–shell nanocomposites (CdS@TiO2 CSNs) was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, and UV–Vis diffuse reflectance spectroscopy (DRS). The as-synthesized sample was utilized for the selective reduction of nitro compounds to benzimidazole and anilide, and also the reduction of benzophenones to alcohol under blue LED irradiation. The 1D CdS@TiO2 CSNs exhibited enhanced photoactivity compared with the pure TiO2, CdS nanowires and commercial TiO2-P25. The excellent reusability of the photocatalyst was examined for six runs. The results demonstrated that the prepared sample has the potential to provide a promising visible light-driven photocatalyst for other organic transformations.
- Eskandari, Parvin,Kazemi, Foad,Ramdar, Moosa,Zand, Zahra
-
-
- GaN nanowires as a reusable photoredox catalyst for radical coupling of carbonyl under blacklight irradiation
-
Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III-V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer. This journal is
- Botton, Gianluigi,Cen, Yunen,Cheng, Shaobo,Li, Chao-Jun,Liu, Mingxin,Mi, Zetian,Rashid, Roksana T.,Tan, Lida
-
p. 7864 - 7870
(2020/08/19)
-
- Light-enabled metal-free pinacol coupling by hydrazine
-
Efficient carbon-carbon bond formation is of great importance in modern organic synthetic chemistry. The pinacol coupling discovered over a century ago is still one of the most efficient coupling reactions to build the C-C bond in one step. However, traditional pinacol coupling often requires over-stoichiometric amounts of active metals as reductants, causing long-lasting metal waste issues and sustainability concerns. A great scientific challenge is to design a metal-free approach to the pinacol coupling reaction. Herein, we describe a light-driven pinacol coupling protocol without use of any metals, but with N2H4, used as a clean non-metallic hydrogen-atom-transfer (HAT) reductant. In this transformation, only traceless non-toxic N2 and H2 gases were produced as by-products with a relatively broad aromatic ketone scope and good functional group tolerance. A combined experimental and computational investigation of the mechanism suggests that this novel pinacol coupling reaction proceeds via a HAT process between photo-excited ketone and N2H4, instead of the common single-electron-transfer (SET) process for metal reductants.
- Qiu, Zihang,Pham, Hanh D. M.,Li, Jianbin,Li, Chen-Chen,Castillo-Pazos, Durbis J.,Khaliullin, Rustam Z.,Li, Chao-Jun
-
p. 10937 - 10943
(2019/12/23)
-
- Lewis Acid Assisted Electrophilic Fluorine-Catalyzed Pinacol Rearrangement of Hydrobenzoin Substrates: One-Pot Synthesis of (±)-Latifine and (±)-Cherylline
-
A microwave-irradiated solvent-free pinacol rearrangement of hydrobenzoin substrates catalyzed by a combination of N-fluorobenzenesulfonimide and FeCl3·6H2O was developed. Its selectivity was first investigated by density functional theory (DFT) calculations. Then the functional group tolerance was examined by synthesizing a series of substrates designed based on the insight provided by the DFT calculations. The application of the methodology was demonstrated by the efficient one-pot synthesis of (±)-latifine and (±)-cherylline, both are 4-aryltetrahydroisoquinoline alkaloids isolated from Amaryllidacecae plants.
- Shi, Hui,Du, Chuan,Zhang, Xinhang,Xie, Fukai,Wang, Xiaoyu,Cui, Shanshan,Peng, Xiaoshi,Cheng, Maosheng,Lin, Bin,Liu, Yongxiang
-
p. 1312 - 1319
(2018/02/09)
-
- MeOH or H2O as efficient additive to switch the reactivity of allylSmBr towards carbonyl compounds
-
A variety of carbonyl compounds were treated by allylSmBr (allylSmBr) with MeOH as the cosolvent to have further insights on the previously reported reductive coupling of aryl ketones mediated by Sm/alkyl halide/MeOH. The results demonstrate that the real reducing species in Sm/alkyl halide/MeOH system should be allylSmBr, and MeOH has elegantly switched the reactivity of allylSmBr from being nucleophilic to being good reductive coupling reagent. Besides, H2O was also found to be a useful additive to realize the pinacol coupling of aliphatic aldehydes and ketones promoted by allylSmBr.
- Li, Jianyong,Niu, Qingsheng,Li, Shanchan,Sun, Yuehao,Zhou, Qian,Lv, Xin,Wang, Xiaoxia
-
supporting information
p. 1250 - 1253
(2017/03/10)
-
- Photochemically-induced C-C bond formation between tertiary amines and nitrones
-
Photoexcited nitrones serve as excellent electron acceptors as well as radical acceptors in the presence of tertiary amines to give β-amino hydroxylamines via photochemically-induced direct sp3 C-H functionalization of the tertiary amines. The combined use of an organophotosensitizer and photoirradiation was highly effective in accelerating addition reactions. Several nitrones and tertiary amines were successfully utilized to give β-amino hydroxylamines in good yield. Highly regioselective generation of primary α-aminoalkyl radicals based on Lewis's stereoelectronic rule and diastereoselective addition reactions of primary α-aminoalkyl radicals with nitrones were successfully achieved. Furthermore, a highly diastereoselective reaction of an α-aminoalkyl radical with a chiral (E)-geometry-fixed α-alkoxycarbonylnitrone was performed.
- Itoh, Kennosuke,Kato, Ryo,Kinugawa, Daito,Kamiya, Hideaki,Kudo, Ryuki,Hasegawa, Masayuki,Fujii, Hideaki,Suga, Hiroyuki
-
supporting information
p. 8919 - 8924
(2015/08/24)
-
- Photoredox-Catalyzed Reductive Coupling of Aldehydes, Ketones, and Imines with Visible Light
-
Ketyl radical and amino radical anions, valuable reactive intermediates for C-C bond-forming reactions, are accessible through a C=O/C=NR umpolung. However, their utilization in catalysis remains largely underdeveloped owing to the high reduction potential of carbonyl compounds and imines. In the context of photoredox catalysis, tertiary amines are commonly employed as sacrificial co-reducing agents. Herein, an additional role of the amine is proposed, in which it is essential for the organocatalytic substrate activation. The combination of photoredox catalysis and carbonyl/imine activation enables the reductive coupling of aldehydes, ketones, and imines under mild reaction conditions.
- Nakajima, Masaki,Fava, Eleonora,Loescher, Sebastian,Jiang, Zhen,Rueping, Magnus
-
supporting information
p. 8828 - 8832
(2015/11/27)
-
- Zn-AlCl3 · 6H2O-mediated reaction in aqueous media: Pinacol coupling reaction
-
(Chemical Equation Presented) Vicinal diols have been prepared in good yield by pinacol coupling reaction of aromatic aldehydes and ketones with commercially available zinc and AlCl3 · 6H2O in water. Copyright Taylor & Francis Group, LLC.
- Hazarika, Binod Kumar,Dutta, Dilip Kumar
-
experimental part
p. 1088 - 1093
(2011/04/25)
-
- Samarium/N-bromosuccinimide-induced reductive dimerization of carbonyl compounds
-
Stereoselective reductive coupling of carbonyl compounds has been achieved using samarium/N-bromosuccinimide in methanol. The combination of these agents has proved a powerful addition to the arsenal of samarium-based reductants currently utilized.
- Banik, Bimal K.,Banik, Indrani,Samajdar, Susanta,Cuellar, Rogelio
-
p. 2319 - 2322
(2007/10/03)
-
- Samarium-induced alkyl halide mediated reductive coupling of ketones
-
Reductive coupling of aromatic ketones was achieved by samarium metal in the presence of alkyl halides. (C) 2000 Published by Elsevier Science Ltd.
- Ghatak, Anjan,Becker, Frederick F.,Banik, Bimal K.
-
p. 3793 - 3796
(2007/10/03)
-
- Ultrasound-promoted samarium/ammonium chloride mediated reductive coupling of aromatic ketones
-
Ultrasound-promoted samarium/ammonium chloride mediated reductive coupling of aromatic ketones was investigated.
- Basu,Becker,Banik
-
p. 406 - 407
(2007/10/03)
-
- Preparation of Condensed Aromatics by Superacidic Dehydrative Cyclization of Arvl Pinacols and Eooxides
-
Aryl pinacols and epoxides, respectively, are cleanly and in high yield converted via superacidic dehydrative cyclization to the corresponding condensed aromatics. Dehydrative cyclization of benzopinacol (1a), triphenylacetophenone (2), and tetraphenylethylene oxide (9) give 9,10-diphenylphenanthrene (3a) as the major product in acidic media stronger than Ho = -11. Aryl pinacol 12a forms the condensed aromatic 13a as the major product in acidic media stronger than Ho = -13.5. It is proposed that the dehydrative cyclizations to provide aromatics 3a and 13a occurs through dicationic intermediates. Substituted benzopinacols 1f, 1g, and 1j are prepared and give the corresponding phenanthrenes (3f, 3g, and 3j) in high yields. The regiochemistry of the cyclization of substituted benzopinacols is controlled by deactivating substituents on the aryl rings. Aryl pinacols (12a-d) derived from acenaphthenequinone and pinacol 15 also give condensed aromatics (13a-d and 16, repectively) with superacidic triflic acid.
- Klumpp, Douglas A.,Baek, Donald N.,Prakash, G.K. Surya,Olah, George A.
-
p. 6666 - 6671
(2007/10/03)
-
- The preparation of substituted phenanthrenes from aryl pinacols in superacid
-
Reactions of aryl pinacols with the superacidic triflic acid give rise to substituted phenanthrenes in good yields.
- Olah,Klumpp,Neyer,Wang
-
p. 321 - 323
(2007/10/03)
-
- Reactions of pinacols with one-electron oxidants
-
Oxidation of the tetraarylpinacols (Ar2COH)2, 1a-e, in which Ar = C6H5 (1a), 4-ClC6H4 (1b), 4-MeC6H4 (1c), 4-MeOC6H4 (1d) and 4-Me2NC6H4 (1e), by thianthrene cation radical (Th?+) in CH3-CN and in CH2Cl2 led quantitatively to the corresponding diaryl ketones Ar2C=O (2a-e), provided a sufficient amount of base, 2,6-di-tert-butyl-4-methylpyridine (DTBMP), was present to prevent presumed acid-catalyzed rearrangement. In the case of 1e, continued oxidation of 2e was also observed. Oxidation of 1a by (4-BrC6H4)3N?+SbCl 6- and (4-BrC6H4)3N?+SbF 6- (Ar3N?+) occurred analogously. Evidence for the catalytic, cation-radical rearrangement of 1a by Ar3N?+ (reported in earlier literature) and by Th?+ could not be found. Quantitative oxidation of 1a to 2a and of 1d to 2d was obtained also with NOBF4, again provided that sufficient DTBMP was present to prevent acid-catalyzed rearrangement. Catalytic, oxidative rearrangement of 1d at room temperature and (as reported in earlier literature) at -5 °C was not observed. Oxidation was also observed of 2,3-diphenyl-2,3-butanediol (3) to acetophenone (9) and of 1,1-dimethyl-2,2-diphenylethanediol (4) to 2a and acetone by Th?+. Oxidation of 2,3-dimethyl-2,3-butanediol (5) by Th?+ was not observed. Instead, even in the presence of DTBMP, pinacolone (10) and tetramethyloxirane (11) were formed, through, it is proposed, a mechanism involving complexation with Th?+.
- Han, Dong Sul,Shine, Henry J.
-
p. 3977 - 3982
(2007/10/03)
-
- Surface modification of CdS quantum dots with fluorinated thiophenol
-
CdS nanocrystallites prepared by capping with pentafluorothiophenol, 2,3,5,6-tetrafluorothiophenol or 4-fluorothiophenol are characterized as quantum dots by TEM, FTIR, NMR, UV-VIS and fluorescence spectroscopy. The crystalline size tends to increase with an increase in the number of fluorine atoms in the capping molecules while maintaining high solubility in organic solvents, with solubility in alcohols depending on the number of fluorine atoms in the capping molecules. Pentafluorophenyl-capped CdS nanocrystallites have the highest solubilities in alcohols, and exhibit quantum dot photocatalysis in methanol, leading to the efficient two-electron transfer photoreduction under visible-light irradiation.
- Hosokawa, Hiroji,Ogata, Tomoyuki,Wada, Yuji,Murakoshi, Kei,Sakata, Takao,Mori, Hirotaro,Yanagida, Shozo
-
p. 4575 - 4580
(2007/10/03)
-
- 2-benzoylbenzoic acid: A photolabile mask for alcohols and thiols
-
Photolysis of 2-benzoylbenzoate esters of primary and secondary alcohols 1 in the presence of a hydrogen donor (2-isopropanol) or an electron donor (primary amines) produces the corresponding alcohol in high yield. The fate of the benzoate is dependent on the conditions used for the photoreaction. In 2-propanol, the ketyl radical that derives from photoreduction dimerizes, to afford the benzpinacol product 3,3"-diphenylbiphthalidyl, 5. In the presence of amines the product is 3-phenylphthalide, 6, a benzhydrol derivative which is the result of simple reduction of the ketone followed by lactonization. While the photoproduct of the benzoate - 2-propanol reaction results from anticipated free radical chemistry, the amine-promoted reaction appears to result from a second, "dark", electron transfer process. We conclude that 2-benzoylbenzoic acid is an effective photolabile protecting group for primary and secondary alcohols, and preliminary studies indicate that thiols can be protected in an analogous way. Studies on the effect of benzophenone substituents and reaction solvent on the benzhydrol:benzpinacol product ratio provide mechanistic insight into the process.
- Jones, Paul B.,Pollastri, Michael P.,Porter, Ned A.
-
p. 9455 - 9461
(2007/10/03)
-
- Semiconductor Photocatalysis: Size Control of Surface-Capped CdS Nanocrystallites and the Quantum Size Effect in Their Photocatalysis
-
Size-controlled CdS nanocrystallites were prepared by using thiophenol or hexanethiol as a capping reagent by controlling the ratio of Cd2+ to bis(trimethylsilyl) sulfide (S(TMS)2) as a source of the sulfide ion in reversed micelles.Their solubility and photocatalysis were examined.A series of size-controlled phenyl-capped CdS nanocrystallites catalyze the photoreduction of aromatic ketones in the presence of triethylamine as an electron donor under visible-light irradiation.The photocatalytic activity is affected by the particle size, i.e., the reducing power of the photogenerated electron on CdS nanocrystallites toward the ketones increases with decreasing the particle size.The enhancement of photocatalytic activity observed by reducing the particle size should be ascribed to not only a negative shift of the conduction band edge, but also suppression of the formation of surface defects.
- Yanagida, Shozo,Ogata, Tomoyuki,Shindo, Akihiro,Hosokawa, Hiroji,Mori, Hirotaro,et al.
-
p. 752 - 758
(2007/10/02)
-
- Semiconductor Photocatalysis: Effect of Light Intensity on Nanoscale CdS-Catalyzed Photolysis of Organic Substrates
-
The relationship between light intensity and product distribution in semiconductor photocatalysis was investigated by using nanoscale CdS microcrystallites (CdS-0) as photocatalysts, triethylamine (TEA) as the electron donor, and either aromatic ketones, electron-deficient alkenes, or 1-benzylnicotinamide (BNA+) as substrates.In the case of the ketones and BNA+, the yield of their respective one-electron reduction products, pinacols and the dimer, (BNA)2, increases with decreasing light intensity.When alkenes are employed in the CdS-0 system, cis-trans photoisomerization always occur regardless of the light intensity.The kinetics for the photocatalysis of the alkanes and the measuement of the inital formation rate of active lattice Cd atoms (Cd0) (which act as catalytic sites for two-electron-transfer reductions) reveal that Cd0 formation is proportional to the square of the relative light intensity, Ir2.The chemoselectivity in the photocatalysis using nanoscale CdS should be affected by the quantity of the Cd0, whose formation strongly depends on the light intensity.
- Shiragami, Tsutomu,Fukami, Shinako,Wada, Yuji,Yanagida, Shozo
-
p. 12882 - 12887
(2007/10/02)
-
- Visible-Light-Induced Two-Electron-Transfer Photoreductions on CdS: Effeects of Morphology
-
Freshly prepared CdS suspensions (CdS-0) consisting of quantized particles and their loose aggregation catalyze photoreductions of aromatic ketones and olefins in methanol under visible light irradiation using triethylamine as sacrificial electron donor, yielding alcohols and dihydro compounds, respectively, which are more selective than photocatalysis of commercially available crystalline CdS (Aldrich) (CdS-Ald).Deuterium incorporation experiments in photolysis of dimethyl maleate in methanol-O-D revealed that CdS-0 catalyzes sequental two-electron-transfer photoreduction, affording dideuterated dimethyl succinate, while CdS-Ald induces both photoreduction and photoisomerization through disproportionation between one-electron-transfer-reduction intermediates, yielding much trideuterated dimethyl succinate and monodeuterated dimethyl fumarate and maleate.
- Shiragami, Tsutomu,Pac, Chyongjin,Yanagida, Shozo
-
p. 504 - 506
(2007/10/02)
-
- Novel reduction of carbonyl compounds with Al/NH3/halide under irradiation of ultrasonic wave
-
Various carbonyl compounds, such as benzophenones and acetophenones, were reduced by Al/NH3/halide under ultrasonic wave irradiation to give the corresponding monohydric alcohols and/or pinacols in satisfactory yields. The addition of inorganic halides improved the selectivity in the formation of monohydric alcohols and pinacols.
- Sato,Nagaoka,Goto,Saito
-
p. 290 - 292
(2007/10/02)
-
- Photochemical Reaction of Benzophenones with Allylic Silanes
-
Photocycloaddition and hydrogen abstraction reactions between benzophenones and allylic silanes have benn investigated.The high regioselective oxetane formations were explained in terms of an stability due to the ?Si-C-p? hyperconjugation of β-silyl radicals in diradical intermediates.Allyl radical substituted by a trimethylsilyl-group, which was generated from a hydrogen abstraction reaction, recombinated with benzophenone ketyl radical at the γ position.No electron transfer products were observed in the reactions.
- Takuwa, Akio,Fujii, Naomi,Tagawa Hiroyuki,Iwamoto, Hidetoshi
-
p. 336 - 338
(2007/10/02)
-
- Nonmetallised CdS-catalised Photoreduction of Aromatic Ketones to Alcohols and/or Pinacols
-
In acatonitrile containing triethylamine as a sacrificial electron donor, non-metallized CdS shows photocatalytic activity for reduction of benzophenone derivatives whose reduction potentials are larger than -1.90 V vs. standard calomel electrode (SCE), giving alcohols and/or pinacols under visible light irradiation.
- Shiragami, Tsutomu,Pac, Chyongjin,Yanagida, Shozo
-
p. 831 - 832
(2007/10/02)
-
- Cp2TiCl2-CATALYZED REACTION OF GRIGNARD REAGENTS WITH DIARYL KETONES, FORMATION OF PINACOLIC COUPLING FROM DIARYL KETONES
-
Diaryl ketones react with Grignard reagents in the presence of a catalytic amount of Cp2TiCl2 to give the corresponding pinacolic coupling products.
- Zhang, Yongmin,Liu, Tianchun
-
p. 2173 - 2178
(2007/10/02)
-
- VIOLOGENS THAT PLUNDER ELECTRON FROM SOLID REDUCING AGENT. REDUCTION OF ARYL KETONES BY ZINC POWDER IN THE PRESENCE OF PROPYL VIOLOGEN AS AN ELECTRON TRANSFER CATALYST
-
It was found that viologen (propyl viologen) acted as an Electron Transfer Catalyst (ETC) in the reduction of aryl ketones with zinc powder. α-Diketones undertook the two-electron reduction to obtain the corresponding benzoins in good yields and aromatic ketones could one-electron reduced selectively to give the corresponding pinacols.
- Endo, Takeshi,Saotome, Yasushi,Okawara, Makoto
-
p. 4525 - 4526
(2007/10/02)
-