Sandmeyer reactions. Part 5. Estimation of the rates of 1,5-aryl/aryl radical translocation and cyclisation during Pschorr fluorenone synthesis with a comparative analysis of reaction energetics

Abstract

During the Pschorr cyclisation of 2-aroylphenyl radicals, a rearrangement occurs reversibly by 1,5-hydrogen transfer to give 2-benzoylaryl radicals. Rate constants of (1.2 ± 0.2) × 10 6 s Ϫ1 at 293 K are estimated for both the forward and back reactions in the equilibrium between 2-(4-methylbenzoyl)phenyl and 2-benzoyl-5-methylphenyl radicals. Assuming an empirical estimate of 1.6 × 10 Ϫ2 dm 3 mol Ϫ1 s Ϫ1 for the hypothetical rate of abstraction of hydrogen from benzene by phenyl radicals, the radical translocation is calculated to occur with a statistically corrected effective molarity of 2.2 × 10 8 mol dm Ϫ3 . By contrast, the competing cyclisation, though occurring at a rate of (8.0 ± 0.9) × 10 5 s Ϫ1 , exhibits an effective molarity of only 5.3 mol dm Ϫ3 . The causes of these differences are analysed in terms of reaction mechanism.

Time-of-Flight Secondary Ion Mass Spectroscopy Characterization of the Covalent Bonding between a Carbon Surface and Aryl Groups

“…59, 60 It has already been observed that the growth of the layer was somewhat impeded in the presence of dioxygen, 25 which is in favor of termination reactions by oxidation. For instance, the hydroxycyclohexadienyl radical is oxidized by Fe(C 2 O 4 ) 3 3-(E°) +0.239 V/SCE) with a rate of 1.30 × 10 6 L mol -1 s -1 and the cyclohexadienyl radicals deriving from 3-methylfluorene-9-one are oxidized in the presence of an excess of hexa-aquacopper(II) with a rate constant >10 7 L mol -1 s -1 .…”

One-Pot Synthesis of Quinoline-2(1H)-thiones from 2-Isocyanostyrenes via Electrocyclic Reaction of the Corresponding 2-Isothiocyanatestyrenes

“…These compounds, except for 1a and 1e, were prepared by treating 2-aminobenzonitriles with arylmagnesium bromides, followed by acidic hydrolysis, according to the procedure reported by Hanson et al 6 (2-Aminophenyl)(4-methoxyphenyl)methanone (1c) The spectral (IR and 1 H NMR) data of this product were identical to those reported previously. 12 (2-Amino-4-chlorophenyl)(4-methylphenyl)methanone (1f) Yield: 76%; yellow solid; mp 115-116 °C (hexane).…”

“…(2-Amininophenyl)phenylmethanone (1a) was commercially available. (2-Aminophenyl)(4-methylphenyl)methanone (1b) was prepared according to the procedure reported by Hanson et al 6 (2-Isocyanophenyl)phenylmethanone (3a) was prepared from 1a via N-(2-benzoylphenyl)formamide (2a) as described previously. 9 1-Isocyano-2-(1-methylethenyl)benzene (4e) was prepared from 2-(1-methylethenyl)benzenamine by the procedure reported previously by us.…”

“…4 A report on the utilization of quinoline-2(1H)-thiones to the synthesis of more complex and important heterocycles has appeared. 5 Our synthesis of 4-substituted quinoline-2(1H)-thiones 6 started mainly from 2-aminophenyl aryl ketones 1, which are commercially available or readily obtained from the reaction of 2-aminobenzonitriles with arylmagnesium bromide followed by acid hydrolysis according to the pro-cedure reported by Hanson et al, 6 as illustrated in Scheme 1. Thus, treatment of 1 with formic acid in refluxing toluene afforded the corresponding N-(2-aroylphenyl)formamides 2, which were then dehydrated with phosphoryl chloride in the presence of triethylamine in THF at 0 °C 7 to afford 2-isocyanophenyl ketones 3.…”

Ring-closure reaction of 2-benzoylbenzenediazonium salts in 1-butyl-3-methylimidazolium ionic liquids

“…High-resolution mass spectral data were recorded with electron impact ionization at 70 eV. Diazonium tetrafluoroborates 1a, 8 1b, 18,19 1c, 18 1d, 18 1e, 20 and 1f 21 12 were prepared using methods similar to those reported in the literature. The other reagents were commercially available and were used as received.…”