38513-66-5Relevant articles and documents
Metal-Free Aerobic Oxidative C–O Coupling of C(sp3)–H with Carboxylic Acids Catalyzed by DDQ and tert-Butyl Nitrite
Pan, Decheng,Pan, Zilong,Hu, Zhiming,Li, Meichao,Hu, Xinquan,Jin, Liqun,Sun, Nan,Hu, Baoxiang,Shen, Zhenlu
, p. 5650 - 5655 (2019/08/20)
The formation of the C–O bond is one of the hot topics in the area of C(sp3)–H bond functionalization. A metal-free oxidative cross-coupling between benzylic C(sp3)–H bond and carboxylic acids has been developed. The reactions were performed with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as the catalyst, tert-butyl nitrite (TBN) as the co-catalyst, and molecular oxygen as the terminal oxidant. A variety of diarylmethanes could be successfully coupled with various carboxylic acids to obtain diarylmethanol esters in good to excellent yields. In addition, 2-benzylbenzoic acids could be converted into phthalides in moderate yields through an intramolecular oxidative cyclization.
DDQ-catalyzed oxidative C-O coupling of sp3 C-H bonds with carboxylic acids
Yi, Hong,Liu, Qiang,Liu, Jie,Zeng, Ziqi,Yang, Yuhong,Lei, Aiwen
, p. 2143 - 2146 (2013/01/15)
Da-ddy, DDQ: By using catalytic amounts of DDQ combined with MnO 2 as oxidant, an efficient oxidative C-O coupling of benzylic sp 3 C-H bonds with carboxylic acids affords a series of carboxylic esters in 70-98 % yields. A wide range
The nature of the transition state in diarylmethyl cation - Nucleophile combination reactions as probed by secondary α-deuterium isotope effects
Van Pham, Thuy,McClelland, Robert A.
, p. 1887 - 1897 (2007/10/03)
Transition-state structures for the carbocation-nucleophile combination reactions of (4-substituted-4′-methoxydiphenyl)methyl cations with water, chloride, and bromide ions in acetonitrile-water mixtures have been investigated by measuring the secondary α-deuterium kinetic and equilibrium isotope effects. Rate constants in the combination direction were measured with laser flash photolysis. Equilibrium constants were measured for the water reaction by a comparison method in moderately concentrated sulfuric acid solutions, for the bromide reaction via the observation of reversible combination, and for the chloride reaction from the ratio of the combination rate constant and the rate constant for the ionization of the diarylmethyl chloride product. The fraction of bond making in the transition state has been calculated as the ratio log (kinetic isotope effect):log (equilibrium isotope effect). For the water reaction, there is 50-65% bond making in the transition state; this is also true for cations that are many orders of magnitude less reactive. The same conclusions, 50-65% bond formation in the transition state independent of reactivity, have previously been made in corre-lations of log kw vs. log KR. Thus, two quite different measures of transition structure provide the same result. The kH:kD values for the halide combinations in 100% acetonitrile are within experimental error of unity. This is consistent with suggestions that these reactions are occurring with diffusional encounter as the rate-limiting step. Addition of water has a dramatic retarding effect on the halide reactions, with rate constants decreasing steadily with increased water content. Small inverse kinetic isotope effects are observed (in 20% acetonitrile:80% water) indicating that carbon-halogen bond formation is rate-limiting. Comparison of the kinetic and equilibrium isotope effects shows ～25 and ～40% bond formation in the transition states for the reactions with bromide and chloride, respectively.
