21370-71-8Relevant academic research and scientific papers
Chemoselective Oxidation of Equatorial Alcohols with N-Ligated λ3-Iodanes
Mikhael, Myriam,Adler, Sophia A.,Wengryniuk, Sarah E.
supporting information, p. 5889 - 5893 (2019/08/26)
The site-selective and chemoselective functionalization of alcohols in complex polyols remains a formidable synthetic challenge. Whereas significant advancements have been made in selective derivatization at the oxygen center, chemoselective oxidation to the corresponding carbonyls is less developed. In cyclic systems, whereas the selective oxidation of axial alcohols is well known, a complementary equatorial selective process has not yet been reported. Herein we report the utility of nitrogen-ligated (bis)cationic λ3-iodanes (N-HVIs) for alcohol oxidation and their unprecedented levels of selectivity for the oxidation of equatorial over axial alcohols. The conditions are mild, and the simple pyridine-ligated reagent (Py-HVI) is readily synthesized from commercial PhI(OAc)2 and can be either isolated or generated in situ. Conformational selectivity is demonstrated in both flexible 1,2-substituted cyclohexanols and rigid polyol scaffolds, providing chemists with a novel tool for chemoselective oxidation.
(Poly)cationic λ3-Iodane-Mediated Oxidative Ring Expansion of Secondary Alcohols
Walters, Jennifer C.,Tierno, Anthony F.,Dubin, Aimee H.,Wengryniuk, Sarah E.
supporting information, p. 1460 - 1464 (2018/04/06)
Herein, a simplified approach to the synthesis of medium-ring ethers through the electrophilic activation of secondary alcohols with (poly)cationic λ3-iodanes (N-HVIs) is reported. Excellent levels of selectivity are achieved for C–O bond migration over established α-elimination pathways, enabled by the unique reactivity of a novel 2-OMe-pyridine-ligated N-HVI. The resulting hexafluoroisopropanol (HFIP) acetals are readily derivatized with a range of nucleophiles, providing a versatile functional handle for subsequent manipulations. The utility of this methodology for late-stage natural product derivatization was also demonstrated, providing a new tool for diversity-oriented synthesis and complexity-to-diversity (CTD) efforts. Preliminary mechanistic investigations reveal a strong effect of alcohol conformation on the reactive pathway, thus providing a predictive power in the application of this approach to complex molecule synthesis.
Alkane oxidation catalysed by a self-folded multi-iron complex
Mettry, Magi,Moehlig, Melissa Padilla,Gill, Adam D.,Hooley, Richard J.
, p. 120 - 128 (2016/11/09)
A preorganised ligand scaffold is capable of coordinating multiple Fe(II) centres to form an electrophilic CH oxidation catalyst. This catalyst oxidises unactivated hydrocarbons including simple, linear alkanes under mild conditions in good yields with selectivity for the oxidation of secondary CH bonds. Control complexes containing a single metal centre are incapable of oxidising unstrained linear hydrocarbons, indicating that participation of multiple centres aids the CH oxidation of challenging substrates.
From DNA to catalysis: A thymine-acetate ligated non-heme iron(III) catalyst for oxidative activation of aliphatic C-H bonds
Al-Hunaiti, Afnan,R?is?nen, Minn?,Repo, Timo
, p. 2043 - 2046 (2016/02/05)
A non-heme, iron(iii)/THA(thymine-1-acetate) catalyst together with H2O2 as an oxidant is efficient in oxidative C-H activation of alkanes. Although having a higher preference for tertiary C-H bonds, the catalyst also oxidizes aliphatic secondary C-H bonds into carbonyl compounds with good to excellent conversions. Based on the site selectivity of the catalyst and our mechanistic studies the reaction proceeds via an Fe-oxo species without long lived carbon centered radicals.
Selective activation of secondary C-H bonds by an iron catalyst: Insights into possibilities created by the use of a carboxyl-containing bipyridine ligand
Cheng, Shi,Li, Jing,Yu, Xiaoxiao,Chen, Chuncheng,Ji, Hongwei,Ma, Wanhong,Zhao, Jincai
, p. 3267 - 3273 (2013/10/01)
In this work, we report the discovery of a carboxyl-containing iron catalyst 1 (FeII-DCBPY, DCBPY = 2,2′-bipyridine-4,4′- dicarboxylic acid), which could activate the C-H bonds of cycloalkanes with high secondary (2°) C-H bond selectivity. A turnover number (TN) of 11.8 and a 30% yield (based on the H2O2 oxidant) were achieved during the catalytic oxidation of cyclohexane by 1 under irradiation with visible light. For the transformation of cycloalkanes and bicyclic decalins with both 2° and tertiary (3°) C-H bonds, 1 always preferred to oxidise the 2° C-H bonds to the corresponding ketone and alcohol products; the 2°/3° ratio ranged between 78/22 and >99/1 across 7 examples. 18O isotope labelling experiments, ESR experiments, a PPh3 method and the catalase method were used to characterize the reaction process during the oxidation. The success of 1 showed that, in addition to using a bulky catalyst, high 2° C-H bond selectivity could also be achieved using a less bulky molecular iron complex as the catalyst.
An iron catalyst for oxidation of alkyl C-H bonds showing enhanced selectivity for methylenic sites
Prat, Irene,Gomez, Laura,Canta, Merce,Ribas, Xavi,Costas, Miquel
supporting information, p. 1908 - 1913 (2013/03/14)
Many are called but few are chosen: A nonheme iron complex catalyzes the oxidation of alkyl C-H bonds by using H2O2 as the oxidant, showing an enhanced selectivity for secondary over tertiary C-H bonds (see scheme). Copyright
Self-terminating radical cyclizations: How are thiyl radicals performing?
Tan, Kristine J.,White, Jonathan M.,Wille, Uta
supporting information; experimental part, p. 4902 - 4911 (2010/11/05)
The performance of thiyl radicals RS' in "self-terminating radical cyclisations" was explored. Using the medium-sized cyclodecyne (1) as model system, the reaction of PhS' generated by photolysis of (PhS)2 was used to study the intermolecular S-radical addition and subsequent intramolecular radical translocations. This reaction resulted in the formation of three stereoisomeric sulfides 17a in very good yield, which all possess the bicyclo[4.4.0]decane framework with either cis and trans ring fusion. The isomeric bicyclo[5.3,0]decane framework was not: formed. Product identification was performed using a combination of techniques, e.g. synthesis of authentic samples, X-ray analysis and computational studies of the potential energy surface, which also revealed valuable insight into the mechanism, of this radical cyclisation cascade. The (PhS)2/PhS' system provides an efficient source for in situ generated thiols, which mediate reduction of the α-thio radical, e.g., 13a→17a. The radical cascade initiated by the addition of BnS', tBuS' or AllylS', respectively, to cycloalkyne 1 was typically terminated also by reduction, even in the absence of an apparent H-donor, and resulted in formation of various bicyclic and monocyclic thioethers. The desired "selftermination", e.g., β-fragmentation of the S-R bond in radical intermediate 12/13 and release of a stabilized radical R', was only observed, as minor reaction, pathway in one particular instance where tBuS' was generated by autoxidation of tBuSH. Computional studies showed that the different stereochemical outcome of the radical cyclizations involving S-radicals, compared to O- or N-centred radicals, could be attributed to the reversibility of the initial intermolecular Sradical addition to the C≡C triple bond in cycloalkyne 1.
The selective functionalization of saturated hydrocarbons. Part 46. An investigation of Udenfriend's system under Gif conditions
Barton, Derek H.R.,Delanghe, Nathalie C.
, p. 4471 - 4476 (2007/10/03)
Under Gif conditions using ascorbic acid as reductant and oxygen as oxidant in pyridine, the selectivity for secondary hydrogen functionalization is exceptional. EDTA (ethylenediamine-tetra-acetic acid) is not needed as a ligand for iron.
Oxidation with the "O2 - H2O2 - Vauauium complex - Pyrazine-2-carboxylic acid" reagent 9. Oxidation of cyclohexene and decalin
Schuchardt,Guerreiro,Shul'pin
, p. 247 - 252 (2007/11/27)
The oxidation of cyclohexene with hydrogen peroxide catalyzed by a vanadium complex and pyrazine-2-carboxylic acid (PCA) in air results in the formation of cyclohex-2-enyl hydroperoxide as the main product and cyclohex-2-enol, cyclohex-2-enone, cyclohex-3-enyl hydroperoxide, cyclohex-3-enol, cyclohexanol, cyclohexane, and 1,2-epoxycyclohexane in lesser amounts. The composition of the products of oxidation of decalin isomers with the system in question is similar to those obtained in the photochemical oxidation with hydrogen peroxide in air and in the oxidation with air in the presence of anthraquinone. A proposed mechanism for the oxidation includes the initiation by hydroxyl radicals generated from hydrogen peroxide under the action of the V - PCA system.
Transannular cyclizations of medium-sized cycloalkynes and cycloalkynones induced by electro- and photochemically generated NO3 radicals
Wille, Uta,Plath, Christian
, p. 111 - 119 (2007/10/03)
Transannular radical cyclizations of medium-sized cycloalkynes and cycloalkynones induced by addition of NO3 radicals to the C-C triple bond were studied. In the reaction of NO3? with medium-sized cycloalkynes oxidation of the triple bond to a carbonyl group occurred and formation of cis-fused bicyclic alkanones by transannular cyclization was observed. In the reaction of NO3 radicals with medium-sized cycloalkynones α,β-epoxy ketones were formed in a transannular reaction sequence which can be formally considered as a retro Eschenmoser-Ohloff fragmentation reaction. The scope and limitations of these reactions are presented and reaction mechanisms are proposed. VCH Verlagsgesellschaft mbH, 1997.
