13901-19-4Relevant academic research and scientific papers
Selectivity and Mechanism of Iridium-Catalyzed Cyclohexyl Methyl Ether Cleavage
Fast, Caleb D.,Jones, Caleb A. H.,Schley, Nathan D.
, p. 6450 - 6456 (2020)
Cationic bis(phosphine)iridium complexes are found to catalyze the cleavage of cyclohexyl methyl ethers by triethylsilane. Selectivity for C-O cleavage is determined by the relative rates of SN2 demethylation versus SN1 demethoxylation, with the axial or equatorial disposition of the silyloxonium ion intermediate acting as an important contributing factor. Modulation of the electron-donor power of the supporting phosphine ligands enables a switch in selectivity from demethylation of equatorial methyl ethers to 2° demethoxylation. Applications of these accessible catalysts to the selective demethoxylation of the 3α-methoxy group of cholic acid derivatives is demonstrated, including a switch in observed selectivity controlled by 7α-substitution. The resting state of the catalyst has been characterized for two phosphine derivatives, demonstrating that the observed switch in C-O cleavage selectivity likely results from electronic factors rather than from a major perturbation of the catalyst structure.
Iron(III)-catalyzed halogenations by substitution of sulfonate esters
Ortega, Nuria,Feher-Voelger, Andres,Brovetto, Margarita,Padron, Juan I.,Martin, Victor S.,Martin, Tomas
experimental part, p. 963 - 972 (2011/06/20)
A novel halogenation reaction from sulfonates catalyzed by iron(III) is described. The reaction can be performed as a stoichiometric or a catalytic version. This reaction provides a convenient strategy for the efficient access to structurally diverse secondary chlorides, bromides and iodides. The stereochemical course of the reaction is governed by the substrate and the experimental conditions. Secondary alcohols modified as quisylates or pysylates are substantially more reactive. Aliphatic quisylates proceed with overall inversion of configuration under catalytic conditions. Chemoselectivity in bismesylates was observed in favour of the secondary mesylate. Additionally, based on the experimental results, a possible catalytic cycle for the halogenation has been proposed.
One-pot reductive cleavage of exo-olefin to methylene with a mild ozonolysis-Clemmensen reduction sequence
Xu, Shu,Toyama, Takayuki,Nakamura, Jun,Arimoto, Hirokazu
scheme or table, p. 4534 - 4537 (2010/10/02)
A one-pot exo-olefin reductive cleavage was for the first time developed. The reaction could proceed under a mild condition avoiding the use of hazardous and expensive reagents. Meanwhile, a TMSCl-mediated Clemmensen reduction in alcoholic solvent was also examined.
Clarification of the stereochemical course of nucleophilic substitution of arylsulfonate-based nucleophile assisting leaving groups
Braddock, D. Christopher,Pouwer, Rebecca H.,Burton, Jonathan W.,Broadwith, Phillip
experimental part, p. 6042 - 6049 (2009/12/24)
(Chemical Equation Presented) Secondary alcohols modified as tosylates, PEG-sulfonates, or quisylates undergo inversion of configuration at the reacting center when treated with lithium halide in acetone at reflux, where the PEG-sulfonates and quisylates are substantially more reactive. In sterically hindered cases, elimination is a competing process. In contrast, when treated with TiCl4, simple secondary sulfonates give chloride products with partial inversion of configuration. Any observed retention of configuration in a given alkyl sulfonate substrate under these conditions is likely due to neighboring group participation or diastereoselective attack on a carbocation (or ion pair) rather than an SNi mechanism.
2-(Prenyloxymethyl)benzoyl (POMB) group: a new temporary protecting group removable by intramolecular cyclization
Vatèle, Jean-Michel
, p. 10921 - 10929 (2008/02/12)
2-(Prenyloxymethyl)benzoates can be prepared from alcohols and readily available 2-(prenyloxymethyl)benzoic acid by standard acylation techniques or by Mitsunobu reaction with inversion of configuration. The POMB group can be cleaved first by oxidative removal of the prenyl group with DDQ followed by lactonization with expulsion of the alcohol catalyzed by Yb(OTf)3. These reaction conditions are compatible with the presence of a large number of common protecting groups.
Chloromethanesulfonate as an efficient leaving group: Rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles
Shimizu, Takeshi,Ohzeki, Tomoya,Hiramoto, Katsuya,Hori, Nobuyuki,Nakata, Tadashi
, p. 1373 - 1385 (2007/10/03)
The chloromethanesulfonate (monochlate) served as an efficient leaving group for rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles. The treatment of the monochlate 16a with zinc acetate in dioxane at 90 °C effected migration of the 4α-methyl group to give alkene 17a. Upon similar treatment of the monochlates 22a, 25a, 28a, and 31a with zinc acetate, the carbon-carbon bonds antiperiplanar to the hydroxyl groups efficiently migrated to afford the alkenes 23a, 26a-c, 29a,b, and 32a, respectively. In the case of the diol 40, the monochlate was converted into the ketone 41 via a rearrangement-ring expansion. The reaction of the monochlates 44a, 47a, 49a, 52a, and 57a with sodium azide or lithium azide in N,N-dimethylformamide efficiently afforded the azides with inversion of the configuration. The introduction of a nitrile group to the sterically hindered alcohol 59 was performed in high yield by the reaction of the monochlate 60a with sodium cyanide.
Nucleophilic Substitution Reactions of (Alkoxymethylene)dimethylammonium Chloride
Barrett, Anthony G. M.,Braddock, D. Christopher,James, Rachel A.,Koike, Nobuyuki,Procopiou, Panayiotis A.
, p. 6273 - 6280 (2007/10/03)
The use of imidate esters as potential replacements for diethyl azodicarboxylate and triphenylphosphine in the Mitsunobu reaction is described. A series of secondary alcohols were allowed to react with (chloromethylene)dimethylammonium chloride, generated from dimethylformamide (DMF) and oxalyl chloride, to give imidate esters. Reaction of these salts with potassium benzoate or potassium phthalimide gave the products of SN2 substitution in excellent yields with clean inversion of stereochemistry. Optimization of reaction conditions is discussed as a means to increase the atom economy of the process by minimizing the quantity of nucleophile required.
Nucleophilic Substitution of (Alkoxymethylene)dimethylammonium Chloride with Carboxylate Salts: a Convenient Procedure for the Synthesis of Esters with Inversion of Configuration
Barrett, Anthony G. M.,Koike, Nobuyuki,Procopiou, Panayiotis A.
, p. 1403 - 1404 (2007/10/02)
Secondary alcohols are converted into benzoate esters with inversion of configuration via sequential reaction with (chloromethylene)dimethylammonium chloride and potassium benzoate.
Electrochemical preparation and some reactions of alkoxy triphenylphosphonium ions
Maeda,Koide,Maki,Ohmori
, p. 1076 - 1080 (2007/10/02)
The formation of an alkoxy triphenylphosphonium ion by anodic oxidation of Ph3P in the presence of an alcohol was investigated. When a CH2Cl2 solution of Ph3P, Ph3P-H·ClO4-, and an alcohol was subjected to constant-current electrolysis in an undivided cell equipped with a graphite anode and a Pt cathode, the 31P-NMR spectra of the resulting electrolyte showed that alkoxy triphenylphosphonium perchlorates (2) were formed in good to fair yields from primary and secondary aliphatic alcohols, while allylic and bencyclic alcohols were transformed to the corresponding alkyl phosphonium ions, and in the case of tertiary aliphatic alcohols, no formation of the corresponding alkoxy or alkyl phosphonium ions was recognized at all. The isolation of 2 thus formed was achieved in good yields by a simple procedure. For the electrolysis, Ph3P+H·BF4- could be utilized instead of the perchlorate salt, giving an alkoxy triphenylphosphonium tetrafluoroborate (3) from primary and secondary aliphatic alcohols. The reaction of the alkoxy phosphonium ion prepared from β- and α-cholestanol with various nucleophiles such as Bu4N+·X- (X = Br, Cl, F, N3, SCN), PhSH, and PhOH was examined. The results indicated that the reaction site of the phosphonium ions is dictated by the identity of the nucleophile. A soft nucleophile was apt to attack at the α-carbon, giving the corresponding SN2 reaction product in a good yield, while a hard one tended to react at the phosphorus of the phosphonium ion, leading to the regeneration of the cholestanol.
