39720-17-7Relevant academic research and scientific papers
Keto-Enol Tautomerization of 2-(2'-Hydroxyphenyl)benzoxazole and 2-(2'-Hydroxy-4'-methylphenyl)benzoxazole in the Triplet State: Hydrogen Tunneling and Isotope Effects. 1 . Transient Absorption Kinetics
Al-Soufi, Wajih,Grellmann, Karl H.,Nickel, Bernhard
, p. 10503 - 10509 (1991)
Hydrogen tunnel effects in the metastable triplet states of 2-(2'-hydroxyphenyl)benzoxazole (HBO) and 2-(2'-hydroxy-4'-methylphenyl)benzoxazole (m-MeHBO) and their deuteriooxy analogues DBO and m-MeDBO have been investigated between 25 and 250 K in three alkane solvents that have drastically different viscosities at low temperatures.In the triplet states of HBO the hydrogen transfer between the enol and keto tautomers is reversible because the two triplet states are isoenergetic.In m-MeHBO the hydrogen transfer is virtually unidirectional because the initially populated keto triplet state has a higher energy than the enol triplet state.In spite of these differences the observed hydrogen-transfer rate constants of the two compounds have nearly the same values.The temperature dependence of the rate constants is insensitive to large changes in solvent viscosity, i. e., hydrogen tunneling in HBO and m-MeHBO depends on solvent friction neither at intermediate nor at very low temperatures.The couples HBO, DBO and m-MeHBO, m-MeDBO are the first examples where the determination of tunneling rate constants has been extended for both isotopomers into a temperature region where the rates and the isotope effect on these rates become temperature independent.
Highly efficient AgNO3-catalyzed approach to 2-(benzo[d]azol-2-yl)phenols from salicylaldehydes with 2-aminothiophenol, 2-aminophenol and benzene-1,2-diamine
He, Xinwei,Wu, Yuhao,Jin, Wenjing,Wang, Xiaoshun,Wu, Cong,Shang, Yongjia
, (2018/02/13)
A new, convenient and efficient AgNO3-catalyzed strategy for the preparation of 2-(benzo[d]azol-2-yl)phenol derivatives in good to excellent yields (63–98%) is described. The reaction proceeds via condensation/intramolecular nucleophilic addition/oxidation process between substituted salicylaldehydes and 2-aminothiophenol, 2-aminophenol or benzene-1,2-diamine under mild reaction conditions. Notably, this reaction utilizes cheap AgNO3 as a readily available and low-cost benign oxidant at low catalyst loadings with excellent functional group tolerance.
Rhodium(III)-Catalyzed ortho-Heteroarylation of Phenols through Internal Oxidative C-H Activation: Rapid Screening of Single-Molecular White-Light-Emitting Materials
Li, Bijin,Lan, Jingbo,Wu, Di,You, Jingsong
, p. 14008 - 14012 (2016/01/25)
Reported herein is the first example of a transition-metal-catalyzed internal oxidative C-H/C-H cross-coupling between two (hetero)arenes through a traceless oxidation directing strategy. Without the requirement of an external metal oxidant, a wide range of phenols, including phenol-containing natural products, can undergo the coupling with azoles to assemble a large library of highly functionalized 2-(2-hydroxyphenyl)azoles. The route provides an opportunity to rapidly screen white-light-emitting materials. As illustrative examples, two bis(triphenylamine)-bearing 2-(2-hydroxyphenyl)oxazoles, which are difficult to access otherwise, exhibit bright white-light emission, high quantum yield, and thermal stability. Also presented is the first example of the white-light emission, in a single excited-state intramolecular proton transfer system, of 2-(2-hydroxyphenyl)azoles, thus highlighting the charm of C-H activation in the discovery of new organic optoelectronic materials.
Samarium(III) triflate: A new catalyst for facile synthesis of benzothiazoles and benzoxazoles from carboxylic acids in aqueous media
Gorepatil, Pratapsinha B.,Mane, Yogesh D.,Gorepatil, Amarsinha B.,Gaikwad, Mahadev V.,Ingle, Vilas S.
, p. 8355 - 8362 (2015/10/20)
A facile synthetic method for benzothiazoles and benzoxazoles comprising the reaction of corresponding 2-aminothiophenol and 2-aminophenol with various substituted aromatic carboxylic acids using Samarium(III) triflate as a catalyst has been described. The advantages of the method are short reaction times and aqueous reaction media and easy work-up. The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of efficiency.
Fluorescence resonance energy transfer between polydiacetylene vesicles and embedded benzoxazole molecules for pH sensing
Seo, Seongwon,Kim, Daigeun,Jang, Geunseok,Kim, Dong-Myung,Kim, Dong Wook,Seo, Bum-Kyoung,Lee, Kune-Woo,Lee, Taek Seung
, p. 451 - 456 (2013/04/10)
A mixed polydiacetylenes (PDAs) vesicle with a phospholipid unit is functionalized by entrapping fluorescent benzoxazole (BZ) molecules inside the PDA vesicles. Upon photo-polymerization and heat-treatment of the self-assembled vesicles, a weak red fluorescence can be observed. Excitation of BZ molecules enables the amplification of PDA vesicle fluorescence resonance energy transfer (FRET) to more than four times that of the direct excitation of red-phase PDA vesicles. The backbone of the PDA vesicles act as energy acceptors, which absorb energy from embedded BZ donor molecules inside the PDA vesicle, which emit blue fluorescence. The amplified red emission from the PDA vesicle can be altered by pH changes in the aqueous solution and thus the PDA vesicle mixed with a phospholipid and entrapped molecules inside can be a promising candidate as a pH sensor.
Keto-enol tautomerism in the triplet state of hydroxyphenylbenzoxazoles in an alkane galss: hydrogen tunneling and isotope effects down to 2 K
Nickel, Bernhard,Grellmann, Karl H.,Stephan, Jens S.,Walla, Peter J.
, p. 436 - 447 (2007/10/03)
2-(2′-HydroxyphenyI)benzoxazole (HBO) and its meta-methyl derivative (m-MeHBO) can exist in two tautomeric forms, an enol tautomer (E) and a keto tautomer (K). The stable ground state is an enol state, 1E, and the lowesi excited singlet state is a keto state, 1K*. Intersystem crossing 1K*3K* is followed by triplet-state tautomerization (TST) 3K*3E* if the energy relation E(3K*) -E(3E*) = hcx > 0 holds. In an alkane glass., the wavenumber x is >0 for ≈90% of all HBO molecules and for virtually all m-MeHBO molecules. The kinetics of TST of HBO, m-MeHBO and of the deuteriooxy analogues DBO and m-MeDBO in an alkane glass was studied between ≈2 and ≈80 K. TST can be observed by measuring the transient absorption after pulsed excitation, due to the different absorption spectra of 3K* and 3E*. The basic results are: (1; TST is a tunnel reaction and its kinetics is independent of temperature between 2 and 25 K. (2) The rate constant kKE of TST depends on the energy difference hex. Due to the wide distribution of x, the kinetics of TST is multiexponenlial; an empirical biexponenliai description of TST yields the ratios k1/k2 ≈ 5 for the rate constants and A1/A2≈2 for the preexponential factors. (3) The wide distribution of the rate constant kKE can be rationalized by a kinetic model, in which the generation of phonons is an important rate-limiting factor. (4) The TST of DBO is ≈ 1700 times slower than that of HBO, and the TST of m-MeDBO is ≈700 times slower than mat of m-MeHBO. - Clear glassy solutions without cracks were obtained by using absorption cells made of polymethylmethacrylate (PMMA), whose thermal expansion coefficient is similar to that of hydrocarbon glasses. WILEY-VCH Verlag GmbH, 1998.
