61066-88-4Relevant academic research and scientific papers
N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading
Berkessel, Albrecht,Biswas, Animesh,Harnying, Wacharee,Sudkaow, Panyapon
supporting information, p. 19631 - 19636 (2021/08/09)
We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02–1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
Enantioselective Synthesis of cis- A nd trans-Borocyclopropylmethanol: Simple Building Blocks to Access Heterocycle-Substituted Cyclopropylmethanols
Charette, André B.,Navuluri, Chandrasekhar,Siddiqui, Saher H.
, p. 3834 - 3846 (2019/10/11)
An enantioselective and non-oxidative methodology was developed to obtain enantioenriched cyclopropyl boronates using a diethanolamine-promoted selective decomplexation of dioxaborolane. The non-oxidative decomplexation of the dioxaborolane ligand from the cyclopropylmethoxide species formed in the dioxaborolane-mediated Simmons-Smith cyclopropanation reaction provided the enantio?-enriched CIDA-based (CIDA = N-cyclohexyliminodiacetic acid) boro?-cyclopropane in 92% yield and 95.6:4.4 er. A robustness screen has shown diethanolamine to be compatible with esters, carbamates and N-heterocycles, providing a tool to access enantioenriched cyclopropanes carrying not only base-sensitive but oxidizable functional groups as well. Diethanolamine was found to be compatible with the modified zinco-cyclopropanation reaction of allyl alcohol to remove residual dioxaborolane from the corresponding cis-N-heterocycle cyclopropylmethanol, thereby leading to improved yields.
Formation of α-SF5-enolate enables preparation of 3-SF5-quinolin-2-ones, 3-SF5-Quinolines, and 3-SF5-pyridin-2-ones: Evaluation of their physicochemical properties
Joliton, Adrien,Plancher, Jean-Marc,Carreira, Erick M.
supporting information, p. 2113 - 2117 (2016/02/18)
This study describes, for the first time, the generation of a SF5-substituted ester enolate from benzyl SF5-acetate under soft enolization conditions, which in turn participates in aldol addition reactions in high yield. The reaction was applied in the synthesis of 3-SF5-quinolin-2-ones, 3-SF5-quinolines, and 3-SF5-pyridin-2-ones, none of which have previously been reported. To provide guidelines for their use in drug discovery, the physicochemical properties of these building blocks were determined and compared with those of their CF3- and t-Bu-analogues.
Oxidation of primary aliphatic and aromatic aldehydes with difluoro(aryl)-λ3-bromane
Ochiai, Masahito,Yoshimura, Akira,Hoque, Md. Mahbubul,Okubo, Takuji,Saito, Motomichi,Miyamoto, Kazunori
supporting information; experimental part, p. 5568 - 5571 (2011/12/03)
Oxidation of primary aliphatic aldehydes with p- trifluoromethylphenyl(difluoro)-λ3-bromane in dichloromethane at 0 °C afforded acid fluorides selectively in good yields, while that of aromatic aldehydes in chloroform at room temperature produced aryl difluoromethyl ethers. A larger migratory aptitude of aryl groups compared to primary alkyl groups during a 1,2-shift from carbon to an electron-deficient oxygen atom in bromane(III) Criegee-type intermediates will result in these differences in the reaction courses.
'Me2CuLi·TMSCl in CH2Cl2'. The most powerful methylating agent for sterically congested α,β-enoates
Asao, Naoki,Lee, Sunyoung,Yamamoto, Yoshinori
, p. 4265 - 4266 (2007/10/03)
The reaction of Me2CuLi with sterically congested α,β-unsaturated esters in the presence of TMSCl in CH2Cl2 proceeded very smoothly to produce the conjugate addition products in high yields.
Novel Template Effects of Distannoxane Catalysts in Highly Efficient Transesterification and Esterification
Otera, Junzo,Dan-oh, Nobushisa,Nozaki, Hitosi
, p. 5307 - 5311 (2007/10/02)
The transesterification of carboxylic esters and the esterification of carboxylic acids are effected under mild conditions under catalysis by 1,3-disubstituted tetraalkyldistannoxanes 1.Various functional groups remain unaffected and otherwise difficult to obtain esters are accessible.An ester bearing a tertiary butyl group in the carboxylic acid moiety remained unchanged in competition experiments with a less bulky ester, which undergoes transesterification quantitatively.The unique features of the reactions are attributable to the template effects of the dimeric structure of 1.The facility with which compounds 1 can be converted into alkoxystannoxanes 2 and the synergistic effect of the proximate tin atoms of 2 play key roles in permitting smooth reactions and high selectivity.Another notable feature of compounds 1 is their unusually high solubility in organic solvents, even though the compounds have a metaloxane core as a major skeletal part.The double-layered structure of 1, in which the inorganic moiety is surrounded by eight alkyl groups, permits esterification to be driven to completion simply by heating a mixture of the carboxylic acid and the alcohol.The distannoxane-catalyzed esterification is irreversible, and thus, no hydrolysis of the product esters occurs when compounds 1 are used as catalysts.
