22460-52-2Relevant academic research and scientific papers
Ni-Catalyzed Formal Cross-Electrophile Coupling of Alcohols with Aryl Halides
Lin, Quan,Ma, Guobin,Gong, Hegui
, p. 14102 - 14109 (2021/11/20)
Direct coupling of unactivated alcohols remains a challenge in current synthetic chemistry. We herein demonstrate a strategy building upon in situ halogenation/reductive coupling of alcohols with aryl halides to forge Csp2-Csp3 bonds. The combination of 2-chloro-3-ethylbenzo[d]oxazol-3-ium salt (CEBO) and TBAB as the mild bromination reagents enables rapid transformation of a wide range of alcohols to their bromide counterparts within one to 5 min in CH3CN and DMF, which is compatible with the Ni-catalyzed cross-electrophile coupling conditions in the presence of a chemical reductant. The present method is suitable for arylation of a myriad of structurally complex alcohols with no need for prepreparation of alkyl halides. More importantly, the mild and kinetically rapid bromination process has shown good selectivity in the bromination/arylation of symmetric diols and less sterically hindered hydroxyl groups in polyols, thus offering promise for selective functionalization of diols and polyols without laborious protecting/deprotecting operations. The practicality of this work is also evident in the arylation of a number of carbohydrates, drug compounds, and naturally occurring alcohols.
Asymmetric Baeyer - Villiger oxidations of 4-mono- and 4,4-disubstituted cyclohexanones by whole cells of engineered Escherichia coli
Mihovilovic,Chen,Wang,Kyte,Rochon,Kayser,Stewart
, p. 733 - 738 (2007/10/03)
Whole cells of an Escherichia coli strain that overexpresses Acinetobacter sp. NCIB 9871 cyclohexanone monooxygenase have been used for the Baeyer-Villiger oxidations of a variety of 4-mono- and 4,4-disubstituted cyclohexanones. In cases where comparisons were possible, this new biocatalytic reagent provided lactones with chemical yields and optical purities that were comparable to those obtained from the purified enzyme or a strain of bakers' yeast that expresses the same enzyme. The efficient production of cyclohexanone monooxygenase in the E. coli expression system (ca. 30% of total soluble protein) allowed these oxidations to reach completion in approximately half the time required for the engineered bakers' yeast strain. Surprisingly, 4,4-disubstituted cyclohexanones were also accepted by the enzyme, and the enantioselectivities of these oxidations could be rationalized by considering the conformational energies of bound substrates along with the enzyme's intrinsic enantioselectivity. The enzyme expressed in E. coli cells also oxidized several 4-substituted cyclohexanones bearing polar substituents, often with high enantioselectivities. In the case of 4-iodocyclohexanone, the lactone was obtained in > 98% ee and its absolute configuration was assigned by X-ray crystallography. The crystal belongs to the monoclinic P21 space group with a = 5.7400(10), b = 6.1650(10), c = 11.377(2) A, b = 99.98(2)°, and Z = 2. Taken together, these results demonstrate the utility of an engineered bacterial strain in delivering useful chiral building blocks in an experimentally simple manner.
Fluorescence Quenching and Photoreactions of 2,3-Diazabicyclooct-2-enes. A Case of Charge Transfer and Hydrogen Atom Transfer
Engel, Paul S.,Kitamura, Akihide,Keys, Dalen E.
, p. 5015 - 5021 (2007/10/02)
A variety of organic compounds have been found to quench the long-lived fluorescence of 2,3-diazabicyclooct-2-ene (DBO), but photochemical reactions take place only with good hydrogen atom donors and tetrahalomethanes.A hydrogen isotope effect on kq of 1.7-3.0 was observed with 1,3- and 1,4-cyclohexadiene.While both quenchers photoreduced DBO, the 1,3-isomer also dimerized to a mixture characteristic of triplet diene.The results are rationalized in terms of the usual encounter complex and ion pair except that the former can undergo hydrogen transfer or react with 1,3-cyclohexadiene.A second case of photochemically induced electron transfer fragmentation was found in the reaction of 1-phenyl-DBO with bromotrichloromethane.
CLEAVAGE OF CYCLIC ETHERS WITH BORON BROMIDE. A CONVENIENT ROUTE TO THE BROMOSUBSTITUTED ALCOHOLS, ALDEHYDES AND KETONES
Kulkarni, Surendra U.,Patil, Vemanna D.
, p. 163 - 167 (2007/10/02)
Cyclic ethers are readily cleaved by BBr3 under mild conditions, providing the corresponding ω-bromoalkylborates (1).Redistribution of 1 with methanol affords ω-bromoalcohols (2).Oxidation of 1 with pyridinium chlorochromate forms the corresponding ω-bromoaldehydes (3).Under these conditions, epoxides yield first the borates of the corresponding bromohydrins, with subsequent oxidation of the intermediate (without isolation), giving the α-bromoketones in high purity and satisfactory yield.
