- Trapping a Highly Reactive Nonheme Iron Intermediate That Oxygenates Strong C-H Bonds with Stereoretention
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An unprecedentedly reactive iron species (2) has been generated by reaction of excess peracetic acid with a mononuclear iron complex [FeII(CF3SO3)2(PyNMe3)] (1) at cryogenic temperatures, and characterized spectroscopically. Compound 2 is kinetically competent for breaking strong C-H bonds of alkanes (BDE ≈ 100 kcal·mol-1) through a hydrogen-atom transfer mechanism, and the transformations proceed with stereoretention and regioselectively, responding to bond strength, as well as to steric and polar effects. Bimolecular reaction rates are at least an order of magnitude faster than those of the most reactive synthetic high-valent nonheme oxoiron species described to date. EPR studies in tandem with kinetic analysis show that the 490 nm chromophore of 2 is associated with two S = 1/2 species in rapid equilibrium. The minor component 2a (～5% iron) has g-values at 2.20, 2.19, and 1.99 characteristic of a low-spin iron(III) center, and it is assigned as [FeIII(OOAc)(PyNMe3)]2+, also by comparison with the EPR parameters of the structurally characterized hydroxamate analogue [FeIII(tBuCON(H)O)(PyNMe3)]2+ (4). The major component 2b (～40% iron, g-values = 2.07, 2.01, 1.95) has unusual EPR parameters, and it is proposed to be [FeV(O)(OAc)(PyNMe3)]2+, where the O-O bond in 2a has been broken. Consistent with this assignment, 2b undergoes exchange of its acetate ligand with CD3CO2D and very rapidly reacts with olefins to produce the corresponding cis-1,2-hydroxoacetate product. Therefore, this work constitutes the first example where a synthetic nonheme iron species responsible for stereospecific and site selective C-H hydroxylation is spectroscopically trapped, and its catalytic reactivity against C-H bonds can be directly interrogated by kinetic methods. The accumulated evidence indicates that 2 consists mainly of an extraordinarily reactive [FeV(O)(OAc)(PyNMe3)]2+ (2b) species capable of hydroxylating unactivated alkyl C-H bonds with stereoretention in a rapid and site-selective manner, and that exists in fast equilibrium with its [FeIII(OOAc)(PyNMe3)]2+ precursor.
- Serrano-Plana, Joan,Oloo, Williamson N.,Acosta-Rueda, Laura,Meier, Katlyn K.,Verdejo, Bego?a,García-Espa?a, Enrique,Basallote, Manuel G.,Münck, Eckard,Que, Lawrence,Company, Anna,Costas, Miquel
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supporting information
p. 15833 - 15842
(2016/01/09)
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- Selective reduction of ketones using water as a hydrogen source under high hydrostatic pressure
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A selective reduction of a broad variety of ketones is described. The method is based on the combination of a Ni-Al alloy and high hydrostatic pressure (HHP, 2.8 kbar) in an aqueous medium. The reaction of the Ni-Al alloy with water provides in situ hydrogen generation and the high pressure ensures that the H2 formed remains in the solution, thus the CO reduction readily occurs. The application of the HHP resulted in selective formation of the desired products and the common problem of non-selective overhydrogenation could be avoided. In most cases the reductions resulted in high yields and excellent selectivities without the use of any base.
- Tomin, Anna,Lazarev, Alexander,Bere, Matthew P.,Redjeb, Hana,T?r?k, Béla
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experimental part
p. 7321 - 7326
(2012/09/22)
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- Orally active and brain permeable proline amides as highly selective 5HT2c agonists for the treatment of obesity
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Brain-penetrable proline amides were developed as 5HT2c agonists with more than 1000-fold binding selectivity against 5HT2b receptor. After medicinal chemistry optimization and SAR studies, orally active proline amides with robust efficacy in a rodent foo
- Liu, Kevin K.-C.,Lefker, Bruce A.,Dombroski, Mark A.,Chiang, Phoebe,Cornelius, Peter,Patterson, Terrell A.,Zeng, Yuan,Santucci, Stephanie,Tomlinson, Elizabeth,Gibbons, Colleen P.,Marala, Ravi,Brown, Janice A.,Kong, Jimmy X.,Lee, Eunsun,Werner, Wendy,Wenzel, Zane,Giragossian, Craig,Chen, Hou,Coffey, Steven B.
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scheme or table
p. 2365 - 2369
(2010/09/03)
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- 2-iodoxybenzenesulfonic acid as an extremely active catalyst for the selective oxidation of alcohols to aldehydes, ketones, carboxylic acids, and enones with oxone
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Electron-donating group-substituted 2-iodoxybenzoic acids (IBXs) such as5-Me-IBX (1g), 5-MeO-IBX (1h), and 4,5-Me2-IBX were superior to IBX 1a as catalysts for the oxidation of alcohols with Oxone (a trad emark of DuPont) under nonaqueous conditions, although Oxone was almost insoluble in most organic solvents. The catalytic oxidation proceeded more rapidly and cleanly in nitromethane. Furthermore, 2-iodoxybenzenesulfonic acid (IBS, 6a) was much more active than modified IBXs. Thus, we established a highly efficient and selective method for the oxidation of primary and secondary alcohols to carbonyl compounds such as aldehydes, carboxylic acids, and ketones with Oxone in nonaqueous nitromethane, acetonitrile, or ethyl acetate in the presence of 0.05-5molpercentof 6a, which was generated in situ from 2-iodobenzenesulfonic acid (7a) or its sodium salt. Cycloalkanones could be further oxidized to α,β- cycloalkenones or lactones by controlling the amounts of Oxone under the same conditions as above. When Oxone was used under nonaqueous conditions, Oxone wastes could be removed by simple filtration. Based on theoretical calculations, we considered that the relatively ionic character of the intramolecular hypervalent iodine-OSO2 bond of IBS might lower the twisting barrier of the alkoxyperiodinane intermediate 16.
- Uyanik, Muhammet,Akakura, Matsujiro,Ishihara, Kazuaki
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supporting information; experimental part
p. 251 - 262
(2009/06/28)
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- A free radical method for reduction of cyclohexanones - Preferential formation of equatorial alcohols
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Cyclohexanones react with 2-hydroselenobenzoic acid to afford spiro-[4H-3,1-benzoxaselenin-2,1′-cyclohexan]-4-ones. Stannane reduction and basic hydrolysis gives epimeric cyclohexanols, with the equatorial isomer predominating.
- Clive, Derrick L. J.,Cheng, Hua
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p. 1951 - 1961
(2007/10/03)
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- Reductions of α,β-unsaturated ketones by NaBH4 or NaBH4 + CoCl2: Selectivity control by water or by aqueous micellar solutions
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Operationally simple and environmentally benign procedures have been developed to selectively reduce different α,β-unsaturated ketones, 4,4- dimethylcyclohex-2-ene-1-one (1), isophorone (2), benzylideneacetone (3), chalcone (4) by NaBH4 or by the system NaBH4 + COCl2. Alternative reaction media to the extensively used MeOH have been explored, and new procedures take advantage of the acceleration and chemoselectivity induced by water or by aqueous micellar solutions. It was possible to selectively and quantitatively afford pure products of 1,2 and of 1,4 reduction as well as the totally reduced compounds (yield and selectivity > 90%) by simple changes in the experimental conditions.
- Aramini, Andrea,Brinchi, Lucia,Germani, Raimondo,Savelli, Gianfranco
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p. 1793 - 1797
(2007/10/03)
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- Lanthanide complexes in organic synthesis: Selective NaBH4 reduction of α,β-unsaturated carbonyl compounds
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The anhydrous lanthanide(III) complexes of N, N'-ethylene-bis(2-aminobenzamide) and N,N'-propylene-bis (2-aminobenzamide) catalyze the sodium borohydride reduction of α, β-unsaturated carbonyl compounds very selectively under ambient conditions. The heavier lanthanide complexes give good yields as compared to their hydrated chloride salts.
- Swamy, S. Jagannatha,Kumar, B. Kishore
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p. 484 - 486
(2007/10/03)
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- THE INFLUENCE OF LITHIUM COMPLEXING AGENTS ON THE REGIOSELECTIVITY OF REDUCTIONS OF SUBSTITUTED 2-CYCLOHEXENONES BY LiAlH4 and LiBH4
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A reversal of regioselectivity of LiAlH4 or LiBH4 reduction of 2-cyclohexenone induced by addition of -cryptand to the reaction medium is accompanied by a rate decrease.In the absence of the cryptand, carbonyl attack predominates (C1:C3=86:14 with LiAlH4 in THF).In the presence of the cryptand, double bond attack is favoured (C1:C3=14:86).This effect is larger with LiAlH4 than with LiBH4.This trend is general in the case of five substituted 2-cyclohexenones.Using 12-crown-4 as a Li+ coordinator, a change in regioselectivity occurs but it is less pronunced than with the cryptand.
- Loupy, Andre,Seyden-Penne, Jacqueline
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p. 1937 - 1942
(2007/10/02)
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- ENZYMATIC "IN VITRO" REDUCTION OF KETONES VII. (1) Reduction rates and stereochemistry of the HLAD catalyzed reduction of 2-alkyl cyclohexanones, dimethyl cyclohexanones, cycloalkanones and bicycloalkanones.
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Values for the rate constants of the catalytic step HLAD-NADH + ketone -> HLAD-NAD1+ + alcohol in the HLAD catalyzed reduction of some 2-alkyl cyclohexanones, geminal dimethyl cyclohexanones, cycloalkanones and bicyclic ketones are presented.Also the thermodynamic parameters of activation are given and they are compared with the activation parameters of the NaBH4 reduction leading to a better understanding of some forces at work in enzymatic catalysis.The results are rationalized in the same way as was previously done for the 3-alkyl and 4-alkyl cyclohexanones.A reaction model is obtained in which steric hindrances and hydrophobic zones are responsible for rate decreasing, respectively increasing interactions between enzyme and substrates.
- Osselaer, T. A. Van,Lemiere, G. L.,Lepoivre, J. A.,Alderweireldt, F. C.
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p. 389 - 398
(2007/10/02)
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