4254-15-3Relevant academic research and scientific papers
Stereochemistry of Nucleophilic Displacement on Two Phosphoric Monoesters and a Phosphoguanidine: The Role of Metaphosphate
Buchwald Stephen L.,Friedman, Jonathan M.,Knowles, Jeremy R.
, p. 4911 - 4916 (1984)
For the role of monomeric metaphosphate and the nature of the transition states in the alcoholysis of phosphoric monoesters to be examined, phenyl phosphate and 2,4-dinitrophenyl phosphate have been synthesized and the stereochemical course of the methanolysis of phenyl phosphate monoanion and of dinitrophenyl phosphate dianion has been evaluated. Phosphocreatine has also been synthesized and the stereochemical course of the methanolysis of this molecule determined.In each case, complete inversion of configuration at phosphorus is observed.It is clear that metaphosphate, if it exists as a true intermediate in these reactions in protic solvent, does not leave the solvent cage in which it is generated.Indeed, product formation occurs more rapidly than rotation of the putative metaphosphate intermediate.These displacements must therefore occur by preassociative mechanisms in which there may be some assistance from the incoming nucleophile.The present results do not allow a distinction to be made between a "preassociative concerted" path (that is, an SN2-like displacement via a very loose transition state) and a "preassociative stepwise" path via a metaphosphate intermediate of very short lifetime.
Stereocontrolled Reduction of 2-Acyl-1,3-oxathiane Derivatives by Zn(BH4)2 and YCl3-NaBH4
Matsubara, Seijiro,Takahashi, Hideya,Utimoto, Kiitiro
, p. 2173 - 2176 (1992)
Both enantiomers of 1,2-alkanediols were prepared by the diastereocontrolled reduction of ketones containing (R)-6-methyl-1,3-oxathiane moiety as a chiral auxiliary; reduction with Zn(BH4)2 selected one diastereoface to give one diastereomer and that with YCl3-NaBH4 produced another diastereomer selectively.
THE CONFIGURATIONS OF (-)-2,3,3-TRIMETHYL-2-HYDROXYBUTANOIC ACID, Me3CC(Me)(OH)CO2H, (-)-3,3,4-TRIMETHYL-3-HYDROXY-1-PENTYNE AND (-)-3-t-BUTYL-3-METHYL-1-CHLOROALLENE
Eliel, Ernest L.,Lynch, Joseph E.,Kenan, William R.
, p. 4813 - 4816 (1987)
The configurations of the title compounds are reassigned, based on stereoselective syntheses of the hydroxyacid and corresponding glycol and application of Cram's, Prelog's and Sharpless' rules.
Mild electrocatalytic hydrogenation of lactic acid to lactaldehyde and propylene glycol
Dalavoy, Tulika S.,Jackson, James E.,Swain, Greg M.,Miller, Dennis J.,Li, Jie,Lipkowski, Jacek
, p. 15 - 28 (2007)
Reduction of fermentation-derived lactic acid (LA) offers a renewables-based pathway to propylene glycol (PG), a large-scale commodity chemical, currently manufactured by the oxidation of petroleum-derived propene. Complementing our previously described catalytic hydrogenation of LA to PG, we now report electrocatalytic hydrogenation (ECH) of LA in an aqueous electrolyte using constant current electrolysis. A reticulated vitreous carbon (RVC) electrode serves to agglomerate, support, and supply current to a 5% Ru/C powder catalyst, the same catalyst used in the classical hydrogenations. The ECH conditions are mild (ambient pressure, 70 °C vs 1500 psi H2, 150 °C) relative to the chemical hydrogenation. More surprisingly, the major electrohydrogenation product is lactaldehyde (LAL), with small quantities of PG also formed. Variable current studies in the range of 10-100 mA show an increase in product yields and a shift in selectivity toward PG with increasing current. Experiments carried out with different acids as electrolytes reveal a distinct effect of the anion on the yields of the two products. In situ ATR-FTIR studies of the ECH of LA point to a chelating bidentate carboxylate adsorption mode for lactate on the Ru surface and offer insight into the effects of electrolyte anions on surface adsorption and reactivity.
Catalytic hydroboration of carbonyl derivatives by using phosphinimino amide ligated magnesium complexes
Cui, Dongmei,Li, Min,Liu, Xinli
supporting information, p. 13037 - 13041 (2021/10/12)
Reduction of carbonyl derivatives by using Earth-abundant, cheap, and environmentally benign metal-based catalysts through an atom-efficient method is a challenging task. Herein, we report the synthesis and characterization of dinuclear magnesium complexes 1-3 chelated by a phosphinimino amide skeleton. In combination with pinacolborane (HBpin) as a reducing agent, complex 1 bearing an ortho-methyl substituent on the phenyl ring of the ligand showed excellent reduction capability for a broad range of carbonyl derivatives under mild reaction conditions. Aldehydes, ketones, and acrolein substrates were efficiently reduced to the corresponding alkoxy-borane products with a record high TOF. Besides, acrolein derivatives were exclusively reduced to 1,2-regioselective products. Using two equiv. of HBpin, ester substrates were reduced to two kinds of alkoxy-borane products. Carbonate reduction accomplished by using complex 1 and three equiv. of HBpin afforded diols and a methanol precursor, respectively. When chiral substrates such as (S)-1,2-propanediol carbonate and l-lactide or polymeric P(l-LA) were employed, the chirality was almost retained in their reductive products.
Enantiodivergent syntheses of (+)- and (?)-1-(2,6-dimethylphenoxy)propan-2-ol: A way to access (+)- and (?)-mexiletine from D-(+)-mannitol
Manna, Avrajit,Chatterjee, Sandip,Chakraborty, Ipsita,Bhaumik, Tanurima
, (2020/01/08)
Chiron approach was used to acquire optically pure (R)- and (S)-1-(2,6-dimethylphenoxy)propan-2-ol, immediate precursors of (S)- and (R)-mexiletines, respectively. Two different routes were followed from a D-mannitol-derived optically pure common precursor to get the enantiomeric alcohols separately. Comparison of their specific rotation values with the corresponding literature values as well as exact mirror-image relationship between their CD curves proved their high enantiopurity. These alcohols were then transformed to the corresponding amine-drugs in an efficient one-step process instead of two steps described in the literature.
Lewis pairs for ring-opening alternating copolymerization of cyclic anhydrides and epoxides
Ji, He-Yuan,Wang, Bin,Pan, Li,Li, Yue-Sheng
supporting information, p. 641 - 648 (2018/02/14)
A simple and highly active catalytic process for ring-opening alternating copolymerization (ROAC) of cyclic anhydrides and epoxides still remains a key challenge. Herein, we have described an effective group of versatile and low-toxic zinc dicarbyl/amine Lewis pairs for the ROAC. The facile route showed a high catalytic activity (TOF ≤ 210 h-1 at 110 °C) and perfectly alternating selectivity (>99%). An unexpected highly regioselective ring-opening of asymmetric epoxides (PO, ECH and SO) was also achieved by the combination of zinc alkyls (or aryls) and amines. Of note, deprotonation side reaction of α-H of anhydrides with organic bases was uncovered, and subsequently was inhibited by using nonpolar solvents and Lewis acid/base pairs. Thus, an array of polyesters was synthesized by the coupling of various anhydrides (PA, CHA, SA and NA) and epoxides (CHO, PO, ECH and SO) using the same Lewis pairs. Furthermore, variable temperature 1H NMR spectral and MALDI TOF MS analyses were performed to understand the possible mechanism and microstructure. The experimental results indicated that zwitterionic alkoxide and carboxylate intermediates alternately formed to enhance the ester repeat units in chain initiation and propagation. This work provides a simple and green catalytic strategy to prepare diversified polyesters from the ROAC process of cyclic anhydrides and epoxides with considerable catalytic activity and alternating selectivity.
In-Situ Monitoring of Enantiomeric Excess during a Catalytic Kinetic Resolution
Mower, Matthew P.,Blackmond, Donna G.
, p. 5977 - 5982 (2018/06/01)
Vibrational Circular Dichroism combined with FTIR spectroscopy (VCD-IR) is demonstrated as a viable tool for the in situ measurement of enantiomeric excess during asymmetric catalytic transformations. Employing the Jacobsen (salen)Co-catalyzed hydrolytic kinetic resolution of racemic epoxides as a proof-of-concept case study, methodology is developed to monitor the enantiomeric excess of the epoxide substrate as a function of conversion of the limiting reactant, water. Comparison of results for monomeric and oligomeric catalysts probes the molecularity of the catalyst by investigating nonlinear effects in catalyst enantiopurity. These results are in excellent agreement with previous mechanistic investigations of this reaction based on kinetic measurements and computational studies.
Kinetic Resolution of 1,2-Diols via NHC-Catalyzed Site-Selective Esterification
Liu, Bin,Yan, Jiekuan,Huang, Ruoyan,Wang, Weihong,Jin, Zhichao,Zanoni, Giuseppe,Zheng, Pengcheng,Yang, Song,Chi, Yonggui Robin
supporting information, p. 3447 - 3450 (2018/06/26)
A kinetic resolution of 1,2-diols bearing both a secondary and a primary alcohol motif through an N-heterocyclic carbene-catalyzed oxidative acylation reaction has been developed. A site- and enantioselective esterification reaction is involved for this process. Both the monoacylated diols obtained and the remaining enantioenriched 1,2-diols are versatile building blocks for the preparation of functional molecules with proven biological activities.
Encapsulation of Homogeneous Catalysts in Mesoporous Materials Using Diffusion-Limited Atomic Layer Deposition
Zhang, Shufang,Zhang, Bin,Liang, Haojie,Liu, Yequn,Qiao, Yan,Qin, Yong
supporting information, p. 1091 - 1095 (2018/01/01)
The heterogenization of homogeneous metal complex catalysts has attracted great attention. The encapsulation of metal complexes into nanochannels of mesoporous materials is achieved by coating metal oxides at/near the pore entrance by diffusion-limited atomic layer deposition (ALD) to produce a hollow plug. The pore size of the hollow plug is precisely controlled on the sub-nanometer scale by the number of ALD cycles to fit various metal complexes with different molecular sizes. Typically, Co or Ti complexes are successfully encapsulated into the nanochannels of SBA-15, SBA-16, and MCM-41. The encapsulated Co and Ti catalysts show excellent catalytic activity and reusability in the hydrolytic kinetic resolution of epoxides and asymmetric cyanosilylation of carbonyl compounds, respectively. This ALD-assisted encapsulation method can be extended to the encapsulation of other homogeneous catalysts into different mesoporous materials for various heterogeneous reactions.
