Highly selective allylic bromination in a bicyclic system (original) (raw)
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J. Org.Chem. 1991, 56, 914-920.pdf
Reactions of thianthrene cation radical perchlorate (Th'+ClO,) with R4Sn, R = methyl (Me), ethyl (Et), n-butyl (Bu), phenyl (Ph), and vinyl, in acetonitrile took place cleanly in the stoichiometric ratio Th'+C1O4?R4Sn 2:l. Oxidative cleavage of R4Sn occurred into R3Sn3+, that was assayed as R3SnC1, and the radical R'. The latter was primarily trapped as the 5-R-thianthreniumyl perchlorate (la-e), although abstraction of hydrogen atom from the solvent was significant in the cases of phenyl and vinyl radicals. Reactions of Th'+C104-with RSnMe3, R = allyl, vinyl, Ph, Et, isopropyl (i-Pr), and tert-butyl (t-Bu), occurred with the same stoichiometry. Exclusive loss of the LPr, t-Bu, and allyl groups occurred. The allyl radical was trapped by Th'+ as 5-allylthianthreniumyl perchlorate (If). The LPr' radicals were mostly and the t-Bu' completely oxidized by Tho+ to the respective cations. Some i-Pr* were trapped by Th'+ as ring-substituted thianthrenes. Loss of vinyl, phenyl, and ethyl radicals was competitive with loss of methyl radical from the corresponding RSnMe3*+, and ratios (R/Me) of loss were measured from the composition of the products that were formed. From reaction of Th'+C104-with R6Sn2 (R = Me and Ph) R3Sn+ was formed exclusively; that is, the R6Sn2 underwent two-electron oxidation.
Supplementary Information Chem. Commun. 2012 D'Errico et al
All the reagents were obtained from commercial sources (Sigma-Aldrich) and were used without further purification. 1 H and 13 C-NMR spectra were acquired on a Varian Mercury Plus 400 MHz and on a Varian Unit Inova 700 MHz in CD 3 OD or CDCl 3 . Chemical shifts are reported in parts per million (δ) relative to the residual solvent signals: CD 2 HOD 3.31 and CHCl 3 7.27 for 1 H-NMR; CD 2 HOD 49.0 and CHCl 3 77.0 for 13 C-NMR. 1 H-NMR chemical shifts were assigned by 2D NMR experiments. The abbreviations s, bs, d, dd and m stand for singlet, broad singlet, doublet, doublet of doublets and multiplet, respectively. HPLC analyses and purifications were carried out on a Jasco UP-2075 Plus pump equipped with a Jasco UV-2075 Plus UV detector using a 4.60 x 150 mm LUNA (Phenomenex) silica column (particle size 5 µm) eluted with a linear gradient of MeOH in AcOEt (from 0 to 5% in 15 min, flow 1.0 mL min -1 , system A), with a linear gradient of AcOEt in n-hexane (from 0 to 100% in 30 min, flow 1.0 mL min -1 , system B) or using a 4.8 x 150 mm C-18 reverse-phase column (particle size 5 µm) eluted with a linear gradient of MeOH in H 2 O (from 0 to 100% in 30 min, flow 1.3 mL min -1 , system C). UV spectra were recorded on a Jasco V-530 UV spectrophotometer. High Resolution MS spectra were recorded on a Bruker APEX II FT-ICR mass spectrometer using electrospray ionization (ESI) technique in positive mode. Elemental analyses were performed on a Thermo Finnigan Flash EA 1112 CHN analyser. IR spectra were recorded on a Jasco FT-IR 430 spectrophotometer. Optical rotations were determined on a Jasco polarimeter using a 1 dm cell at 25 °C; concentrations are in g/100 mL. Preparative PLC chromatography was performed using F254 silica gel plates (0.5 mm thick, Merck). Analytical TLC analyses were performed using F254 silica gel plates (0.2 mm thick, Merck). TLC spots were detected under UV light (254 nm). For MTS assays the UV absorbance at 490 nm was read using a Beckman Anthos 96 well Microplate Reader.
The Journal of Physical Chemistry A, 1999
Cavity ring-down spectroscopy (CRDS), end-product analysis, and ab initio calculations have determined absorption cross sections, rate coefficients, reaction mechanisms, and thermochemistry relevant to the addition of halogen atoms to propargyl chloride and propargyl bromide. Halogen atoms were produced by laser photolysis, and the addition reaction products were probed at a variable delay by CRDS using a second laser pulse. We report the continuum spectra of C 3 H 3 Cl 2 (1,2-dichloroallyl), C 3 H 3 ClBr (1-chloro-2-bromoallyl), and C 3 H 3 Br 2 (1,2-dibromoallyl) radicals between 238 and 252 nm and the absorption cross sections, σ 240 (C 3 H 3 -Cl 2 ) ) (4.20 ( 1.05) × 10 -17 cm 2 molecule -1 and σ 242 (C 3 H 3 Br 2 ) ) (1.04 ( 0.31) × 10 -17 cm 2 molecule -1 . When the observed data are fit to complex reaction schemes, the 298 K rate coefficients for formation of 1,2-dihaloallyl radicals at 665 Pa were found to be k(Cl + C 3 H 3 Cl) ) (1.2 ( 0.2) × 10 -10 cm 3 molecule -1 s -1 and k(Br + C 3 H 3 Br) ) (2 ( 1) × 10 -12 cm 3 molecule -1 s -1 . At 298 K and 665 Pa the self-reaction rate coefficients of these radicals were found to be k(C 3 H 3 Cl 2 + C 3 H 3 Cl 2 ) ) (3.4 ( 0.9) × 10 -11 cm 3 molecule -1 s -1 and k(C 3 H 3 Br 2 + C 3 H 3 Br 2 ) ) (1.7 ( 1.1) × 10 -11 cm 3 molecule -1 s -1 . The listed uncertainties are twice the standard deviation of individual determinations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section. † NIST/NRC Postdoctoral Associate 1995-1997.
J. Am.Chem.Soc. 1988, 110, 3247-3252.pdf
Acid-catalyzed rearrangement of 6-bromo-2,4-dimethyl-4-(phenylamino)cyclohexa-1 ,4-dienone (1, a quinamine) in aqueous methanol gives, from a so-called quinamine rearrangement, 4'-amino-6-bromo-2,4-dimethyldiphenyl ether (2) and a number of byproducts. The ratio of yield of 2 to that of byproducts is 76:24. The byproducts are, mostly, 1,3-dimethylcarbazole (7) and some of its derivatives, the relative yields of which depend on the concentration of the catalyzing acid, HCI. The major byproduct in low HC1 concentrations is 1,3-dimethyl-4-methoxycarbazole (9). Kinetic isotope effects (KIE) were measured for the formation of 2 from 1, which was labeled at the carbonyl oxygen atom (['*0]-1), the nitrogen atom ([I5N]-1), and the para position of the aniline ring ([4-I4C]-1). The KIE (averages) were as follows: k ( ' 6 0 ) / k ( 1 8 0 ) , 1.0399; k(I4N)/k(l5N), 1.0089; /~( ' * c ) / k (~~C ) , 1.0501. The results suggest that the formation of 2 is a concerted process, a [5,5]-sigmatropic rearrangement, and not a two-step one, going through the rate-determining formation of a r-complex. KIE were measured for the formation of both 2 and 9 from 1, which was labeled in the ortho position of the anilino ring ([2-14C]-1). The KIE [k(12C)/k(14C)] were respectively 0.9895 and 1.0697. These results suggest that the byproduct (9) is formed by a concerted process, too, a [3,3]-sigmatropic rearrangement to an intermediate , which continues on to 9 and the other byproducts. The results show also that 2 cannot be formed from 1 by a succession of two [3,3]-sigmatropic rearrangements, the first of which is to 14. Thus, the quinamine rearrangements. on the basis of our results with 1, appear to be concerted, rather than a-complex intermediate, processes.
Russ. Chem. Rev. 2005, 74, 639-669
The published data on the intramolecular Diels ± Alder The published data on the intramolecular Diels ± Alder reaction in compounds of the 2-alkenylfuran series are general-reaction in compounds of the 2-alkenylfuran series are generalised. The methods and conditions for the preparation of tricyclic ised. The methods and conditions for the preparation of tricyclic systems are considered. The effects of the substituents in the furan systems are considered. The effects of the substituents in the furan and the unsaturated fragments on the cycloaddition are discussed. and the unsaturated fragments on the cycloaddition are discussed. The application of this reaction to the synthesis of alkaloids and The application of this reaction to the synthesis of alkaloids and terpenoids is exemplified. The bibliography includes 168 referen-terpenoids is exemplified. The bibliography includes 168 references ces. .
J. Org.Chem. 1982, 47, 3199-3207.pdf
The behavior of cyclic thiolsulfiiates 5 and 6 (dibenzo[c,e]-l,2-dithiin 1-oxide and naphtho[l,&cd]-l,2-dithiole 1-oxide) upon treatment with either sulfite, cyanide, or t-Bus-ions has been examined and compared with the behavior of the corresponding thiolsulfonates 1 and 2 (dibemo[c,e]-1,2-dithiin and naphtho[l,&cd]-l,2-dithiole 1,l-dioxides). Very marked differences are observed. Whereas thiolsulfonates 1 and 2 are converted essentially quantitatively to ring-open substitution produds (3 and 4) upon treatment with exceas sulfite, cyanide, or t-Bus-, with thiolsulfiites 5 and 6 the equilibrium constants for opening of the sulfur-containing ring are so much smaller that only in the case of 5 and t-Bus-is the equilibrium constant large enough that a significant fraction of the thiolsulfinate is converted to the ring-opened product (7 or 8) at equilibrium. Kinetic studies of the rates of nucleophilmtalyzed racemization of optically active 5 and 6 show that the major factor reaponsible for the dramatic difference in the magnitude of the equilibrium constants is not a decrease in the rate constant for opening of the ring by the nucleophile but rather a huge increase in the rate constant for the reverse of the ring-opening reaction, which in the case of the thiolsulfinates involves displacement of the nucleophile (Nu-) from SNu by a sulfenate (SO-) group, whereas for the thiolsulfonates it is a sulfinate (SOz-) group that performs the same displacement. In the 5-t-BUS-system the rate constant for the displacement by the sulfenate is 30 OOO times faster than the rate constant for the corresponding displacement in the 1-t-Bus-system involving the sulfmate; this provides the first quantitative measure of just how much more reactive a sulfenate ion is as a nucleophile than the corresponding sulfinate. Other aspects of the kinetics of the reactions of 5 and 6 with these nucleophiles provide additional information on the behavior of 7 and 8 and their conjugate acids and thereby furnish new insight into the chemistry and reactivity and of arenesulfenates and arenesulfenic acids.
J. Org.Chem. 1983, 48, 995-1000.pdf
J. Org. Chem. the relative ease of formation of the intermediates (IB > I H ) , while the slopes (greater a t lower pH) may reflect the relative ease of trapping of the two intermediates.
Croat. Chem. Acta 2015, 88(3), 259–266.pdf
Redox kinetics of the reaction of an adipato bridged iron(III)-salen complex, [(Fe(salen))2adi] with dithionite ion, S2O4 2-, was investigated in perchloric acid at I = 0.05 mol dm -3 (NaClO4) and T = 29 ± 1 °C. Spectrophotometric titrations indicated consumption of one mole of S2O4 2per mole of [(Fe(salen))2adi] reduced. Under pseudo-first order conditions of [S2O4 2-] above ten-fold excess of concentration of [(Fe(salen))2adi], observed rates increased with increase in [S2O4 2-] and second order rate constants were fairly constant (0.285 ± 0.01 dm 3 mol -1 s -1 ) indicating first order dependence of the rate on [(Fe(salen))2adi]. A plot of logkobs versus log[S2O4 2-] was linear and gave a slope of 1.0 indicating first order dependence of the rate on [S2O4 2-]. The reaction rate increased with increase in [H + ] within 3 × 10 -3 mol dm -3 ≤ [H + ] ≤ 14 × 10 -3 mol dm -3 . The reaction was unaffected by variation of ionic strength and dielectric constant of the medium. Addition of anion and cation did not catalyze the reaction. The reaction has been analyzed on the basis of an inner-sphere mechanism mediated by proton transfer.