Halide exchanged Hoveyda-type complexes in olefin metathesis

• Julia Wappel,
• César A. Urbina-Blanco,
• Mudassar Abbas,
• Jörg H. Albering,
• Robert Saf,
• Steven P. Nolan and
• Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

• propagation rate constant decreases with increasing steric demand of the halo ligands (i.e., kp(1) > kp(2) >> kp(3)) and the ratio of initiation rate to propagation rate increases on going from 1 to 2 (i.e., ki/kp(1) < ki/kp(2) ≈ ki/kp(3) > 1) but remains of the same order of magnitude. By studying the

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• ]. Eckart-barrier approach For evaluation of the rate constant k, the activation barriers of the forward and back reaction, Vf and Vb, were computed, along with the imaginary frequency νi of the transition state and the frequency νξ, corresponding to the reaction coordinate. All energies were vibrationally

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• obey the same rate equation, but the reaction in propylene carbonate has an observed second-order rate constant a factor of four smaller than the reaction in dichloromethane, consistent with the lower conversions observed for reactions carried out in propylene carbonate (Table 1). To determine the

• at each catalyst concentration were determined in triplicate, using two different batches of propylene carbonate, and the average value of the rate constant was calculated from all three data points for each concentration. As shown in Figure 3, plots of k2obs against the concentration of catalyst 2

• temperatures between 253 and 293 K. The resulting rate data are presented in Table 4. The corresponding Eyring plot is shown in Figure 4. The Eyring equation (Equation 2) relates the rate constant for a reaction to the enthalpy and entropy of activation. Replacing the actual rate constant in Equation 2 with

β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

• Jaya S. Kudavalli and
• Rory A. More O'Ferrall

Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118

• solvolysis to be assessed, a rate constant for solvolysis of the corresponding tetrahydronaphthalene substrate lacking a β-hydroxy group, namely 1-chloro-1,2,3,4-tetrahydronaphthalene (5), has been measured. Results Cis- and trans-1-trichloroacetoxy-2-methoxy-1,2-dihydro-naphthalenes (3) Rate constants for

• water. A rate constant in water for the cis-substrate was extrapolated from measurements at different solvent compositions plotted as log k against YOTs (Supporting Information File 1, Figure S1) [4][5]. For the trans isomer the solvolysis was too slow for measurements over a wide range of solvent

• compositions and rate constants could conveniently be measured only for 10 and 20% (v/v) acetonitrile. A rate constant in water was crudely extrapolated from the ratio of rate constants for the cis and trans isomers at these two solvent compositions. Values in water are shown in brackets in Table 1. In the

Flow through reactors for organic chemistry: directly electrically heated tubular mini reactors as an enabling technology for organic synthesis

• Ulrich Kunz and
• Thomas Turek

Beilstein J. Org. Chem. 2009, 5, No. 70, doi:10.3762/bjoc.5.70

• time during the experimental run. c0 is the initial concentration of the ester and c is the current concentration, both in mol L−1. From the experiments 19 values for the reaction rate constant k could be calculated which were used to prepare an Arrhenius plot. This plot (Figure 3) was used to estimate

Preparation and Diels–Alder/cross coupling reactions of a 2-diethanolaminoboron- substituted 1,3-diene

• Liqiong Wang,
• Cynthia S. Day,
• Marcus W. Wright and
• Mark E. Welker

Beilstein J. Org. Chem. 2009, 5, No. 45, doi:10.3762/bjoc.5.45

• –100 °C in a sealed tube in toluene with N-phenylmaleimide to obtain >90% yield of cycloadduct, the diethanolamine boronyl diene 2 reacted with this same dienophile to afford a 98% isolated yield of cyclaooduct 4 after only 15 min at 25 °C! We tried to get more quantitative rate constant data about

From discovery to production: Scale- out of continuous flow meso reactors

• Peter Styring and
• Ana I. R. Parracho

Beilstein J. Org. Chem. 2009, 5, No. 29, doi:10.3762/bjoc.5.29

• product so the possibility arises that the catalyst takes an alternative pathway (route B) once the catalyst initiation has occurred. As the cross-coupled product is observed as the highest yielding product, it was proposed that the rate constant for route A is smaller than for route B. The proposed

Part 1. Reduction of S-alkyl- thionocarbonates and related compounds in the presence of trialkylboranes/air

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 45, doi:10.1186/1860-5397-3-45

• by 1H NMR. Regardless of the temperature, the yield of the reduction exceeds 82%. It is important to note that, at 20°C, the rate of reduction equals the rate of the 1,2-acetyl group migration. The rate constant for the latter process has been estimated to be 4.0 x 102 s-1 in benzene at 75°C.[26] We

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• cyclizations of 11b, so the related α-acyloxy radical fragmentations to give acyl radicals could have rate constants as high as 103 – 104 s-1. However, the results can also be interpreted through the intermediacy of cationic precursors of ketones produced by radical oxidation, in which case the rate constant