619-25-0Relevant articles and documents
Transition State Differences in Hydrolysis Reactions of Alkyl versus Aryl Phosphate Monoester Monoanions
Grzyska, Piotr K.,Czyryca, Przemyslaw G.,Purcell, Jamie,Hengge, Alvan C.
, p. 13106 - 13111 (2003)
Although aryl phosphates have been the subject of numerous experimental studies, far less data bearing on the mechanism and transition states for alkyl phosphate reactions have been presented. Except for esters with very good leaving groups such as 2,4-dinitrophenol, the monoanion of phosphate esters is more reactive than the dianion. Several mechanisms have been proposed for the hydrolysis of the monoanion species. 18O kinetic isotope effects in the nonbridging oxygen atoms and in the P-O(R) ester bond, and solvent deuterium isotope effects, have been measured for the hydrolysis of m-nitrobenzyl phosphate. The results rule out a proposed mechanism in which the phosphoryl group deprotonates water and then undergoes attack by hydroxide. The results are most consistent with a preequilibrium proton transfer from the phosphoryl group to the ester oxygen atom, followed by rate-limiting P-O bond fission, as originally proposed by Kirby and co-workers in 1967. The transition state for m-nitrobenzyl phosphate (leaving group pKa 14.9) exhibits much less P-O bond fission than the reaction of the more labile p-nitrophenyl phosphate (leaving group pKa = 7.14). This seemingly anti-Hammond behavior results from weakening of the P-O(R) ester bond resulting from protonation, an effect which calculations have shown is much more pronounced for aryl phosphates than for alkyl ones.
Reactivity of secondary N-alkyl acrylamides in Morita–Baylis–Hillman reactions
Ahmar, Mohammed,Queneau, Yves,Verrier, Charlie,Yue, Xiaoyang
, p. 319 - 330 (2021/10/29)
The Morita–Baylis–Hillman (MBH) reaction of secondary N-alkyl acrylamides, discarded up to now from investigations of the scope of activated alkenes, was studied. Optimization of the reaction conditions revealed that a balance must be found between activation of the MBH coupling reaction and that of the undesired competitive aldehyde Cannizzaro reaction. Using 3-Hydroxyquinuclidine (3-HQD) in a 1:1 water-2-MeTHF mixture provides the appropriate conditions that were applicable to a wide range of diversely substituted secondary N-alkyl acrylamides and aromatic aldehydes, giving rise to novel amide-containing MBH adducts under mild and clean conditions.
Hydroboration Reaction and Mechanism of Carboxylic Acids using NaNH2(BH3)2, a Hydroboration Reagent with Reducing Capability between NaBH4and LiAlH4
Wang, Jin,Ju, Ming-Yue,Wang, Xinghua,Ma, Yan-Na,Wei, Donghui,Chen, Xuenian
, p. 5305 - 5316 (2021/04/12)
Hydroboration reactions of carboxylic acids using sodium aminodiboranate (NaNH2[BH3]2, NaADBH) to form primary alcohols were systematically investigated, and the reduction mechanism was elucidated experimentally and computationally. The transfer of hydride ions from B atoms to C atoms, the key step in the mechanism, was theoretically illustrated and supported by experimental results. The intermediates of NH2B2H5, PhCH= CHCOOBH2NH2BH3-, PhCH= CHCH2OBO, and the byproducts of BH4-, NH2BH2, and NH2BH3- were identified and characterized by 11B and 1H NMR. The reducing capacity of NaADBH was found between that of NaBH4 and LiAlH4. We have thus found that NaADBH is a promising reducing agent for hydroboration because of its stability and easy handling. These reactions exhibit excellent yields and good selectivity, therefore providing alternative synthetic approaches for the conversion of carboxylic acids to primary alcohols with a wide range of functional group tolerance.
KB3H8: An environment-friendly reagent for the selective reduction of aldehydes and ketones to alcohols
Li, Xinying,Mi, Tongge,Guo, Wenjing,Ruan, Zhongrui,Guo, Yu,Ma, Yan-Na,Chen, Xuenian
supporting information, p. 12776 - 12779 (2021/12/10)
Selective reduction of aldehydes and ketones to their corresponding alcohols with KB3H8, an air- and moisture-stable, nontoxic, and easy-to-handle reagent, in water and THF has been explored under an air atmosphere for the first time. Control experiments illustrated the good selectivity of KB3H8 over NaBH4 for the reduction of 4-acetylbenzaldehyde and aromatic keto esters. This journal is