40237-73-8Relevant articles and documents
Mechanistic Insights into the Chemo- And Regio-Selective B(C6F5)3 Catalyzed C-H Functionalization of Phenols with Diazoesters
Zhang, Qi,Zhang, Xiao-Fei,Li, Mo,Li, Cheng,Liu, Jia-Qin,Jiang, Yuan-Ye,Ji, Xin,Liu, Lu,Wu, Yu-Cheng
, p. 14508 - 14519 (2019/11/14)
The Lewis acidic B(C6F5)3 was recently demonstrated to be effective for the C-H alkylation of phenols with diazoesters. The method avoids the general hydroxyl activation in transition-metal catalysis. Ortho-selective C-H alkylation occurs regardless of potential para-selective C-H alkylation and O-H alkylation. In the present study, a theoretical calculation was carried out to elucidate the reaction mechanism and the origin of chemo- and regio-selectivity. It is found that the previously proposed B(C6F5)3/N or B(C6F5)3/C bonding-involved mechanisms are not favorable, and a more favored one involves the B(C6F5)3/C=O bonding, rate-determining N2 elimination, selectivity-determining electrophilic attack, and proton transfer steps. Meanwhile, the new mechanism is consistent with KIE and competition experiments. The facility of the mechanism is attributed to two factors. First, the B(C6F5)3/C=O bonding reduces the steric hindrance during electrophilic attack. Second, the bonding forms the conjugated system by which the LUMO energy is reduced via the electron-withdrawing B(C6F5)3. The ortho-selectivity resulted from the greater ortho-C-C (than para-C-C) interaction and the O-H···O and O-H···F hydrogen-bond interaction during electrophilic attack. The greater C-C (than C-O) interaction and the π-πstacking between the benzene rings of phenol and diazoester concerted contribute to the chemo-selective C-H alkylation.
Photochemical and Thermal Transformations of 2(3H)-Furanones and Bis(benzofuranones). A Laser Flash Photolysis study
Lohray, B. B.,Kumar, C. V.,Das, P. K.,George, M. V.
, p. 7352 - 7359 (2007/10/02)
Transformations of the 2(3H)-furanones 1-4 and bis(benzofuranones) 16-18 under steady-state photolysis and thermolysis are reported.Irradiation of 1 in benzene gives a mixture of the decarbonylated product 5 (62percent) and the cyclized phenanthrene derivative 10 (15percent).Similar results were obtained when the photolysis of 1 was carried out in methanol and acetone.Irradiation of 2 in benzene and methanol gave exclusively the decarbonylation product 6, whereas, in acetone, a mixture of the rearranged lactone 13 and and its cyclized product, 15, was obtained.Irradiation of both 3 and 4 gave the cyclized products 11 and 12, respectively.In contrast, the photolysis of the bis(benzofuranone) 16 in cyclohexane gave 3-phenylbenzo-2-(3H)-furanone (25), whereas the photolysis in methanol led to a mixture of methyl α-(2-hydroxyphenyl)phenylacetate (34) and 3-hydroxy-3-phenylbenzo-2(3H)-furanone (31).Similar results were obtained in the irradiation of 17 and 18.Neat thermolysis of furanones 1-3 at 350-450 deg C gave the decarbonylated products 5, 6, and 37 in 36-80 percent yields, whereas furanone 4 underwent facile isomerization to 5-benzyl-3,4,5-triphenyl-2(5H)-furanone (38), upon refluxing in diphenyl ether (ca. 255 deg C).Heating of bis(benzofuranones) 16-18 in refluxing cumene (ca. 150 deg C) gave the corresponding furanones 25-27 in 62-68 percent yields.Laser flash photolysis of furanones 1-4 at 248 and 337 nm leads to absorption spectral changes that can be explained in terms of singlet-mediated decarbonylation (φ = 0.3 for 2 in methanol, λex = 248 nm) and cyclization, i.e., dihydrophenanthrene formation (φ = 0.1-0.5 for 1, 3, and 4 in benzene and methanol, λex = 337 nm).The triplets of the furanones generated under energy-transfer sensitization by benzophenone in benzene are relatively long lived (r = 1.2-12 μs) and exhibit absorption maxima at 330-370 nm (εmax = (11-14) * 103 M-1 cm-1); these spectral and kinetic features appear to be characteristic of the styrene and cis-stilbene chromophores, constrained into planar configurations.Upon laser flash photolysis at 248 nm in methanol, bis(benzofuranones) 16-18 undergo facile fragmentation to the corresponding radicals 19-21, characterized by sharp and intense absorption maxima at ca. 330 nm, in addition to broad and weak absorption band systems at 500-600 nm; these radical species are the primary intermediates implicated in the formation of various final products in the course of steady-state photolysis of 16-18 under different conditions.
