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Dneprovskii, A. S.; Eliseenkov, E. V.; Chulkova, Tatiana G.

doi:10.1023/a:1016365605288

Cited by 6 publications

(5 citation statements)

References 11 publications

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“…CBrCl 3 and N -bromosuccinimide (NBS) give rapid (ca. 10 8 L·mol -1 s -1 ) Br atom transfer to alkyl radicals. With ibuprofen and C MR (IV,IV) , CBrCl 3 and NBS (0.125 M, 5 equiv vs substrate) did not yield any halogenated product (Table ) suggesting that the half-life of the radical formed must be ≤10 -7 s. This indicates the “rebound” happens at a rate >10 8 L·mol -1 s -1 .…”

Section: Resultsmentioning

confidence: 99%

High Turnover Remote Catalytic Oxygenation of Alkyl Groups: How Steric Exclusion of Unbound Substrate Contributes to High Molecular Recognition Selectivity

2008

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H-bonding mediated molecular recognition between substrate and ligand -COOH groups orients the substrate so that remote, catalyzed oxygenation of an alkyl C-H bond by a Mn-oxo active site can occur with very high (>98%) regio- and stereoselectivity. This paper identifies steric exclusion-exclusion of non H-bonded substrate molecules from the active site-as one requirement for high selectivity, along with the entropic advantage of intramolecularity. If unbound substrate molecules were able to reach the active site, they would react unselectively, degrading the observed selectivity. Both of the faces of the catalyst are blocked by two ligand molecules each with a -COOH group. The acid p-(t)BuC6H4COOH binds to the ligand -COOH recognition site but is not oxidized and merely blocks approach of the substrate therefore acting as an effective inhibitor for ibuprofen oxidation in both free acid and ibuprofen ester form. Dixon plots show that inhibition is competitive for the free acid ibuprofen substrate, no doubt because this substrate can compete with the inhibitor for binding to the recognition site. In contrast, inhibition is uncompetitive for the ibuprofen-ester substrate, consistent with this ester substrate no longer being able to bind to the recognition site. Inhibition can be reversed with MeCOOH, an acid that can competitively bind to the recognition site but, being sterically small, no longer blocks access to the active site.

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Section: Resultsmentioning

confidence: 99%

High Turnover Remote Catalytic Oxygenation of Alkyl Groups: How Steric Exclusion of Unbound Substrate Contributes to High Molecular Recognition Selectivity

2008

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“…The relative rate constants k(XHlg 1 )/k(YHlg 2 ) for halogen abstraction from ArSO 2 Cl, ArSO 2 NCl 2 , and ArICl 2 were reported in [2].…”

Section: Methodsmentioning

confidence: 99%

“…On the other hand, general relations holding in halogen transfer to alkyl radicals have been studied poorly. Therefore, we examined the effect of the structure of organic halogen compounds on the rate of halogen transfer therefrom to alkyl radicals.We determined the relative rate constants for abstraction of chlorine and bromine atoms from halogenating agents and arenesulfonyl chlorides by cyclohexyl and benzyl radical, following the procedure developed previDeceased.ously [2]. This procedure is based on competing abstraction of halogen from reagents XHlg 1 and YHlg 2 by alkyl radicals generated by radical chain halogenation of the corresponding alkane under conditions excluding formation of molecular halogen.…”

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confidence: 99%

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Structural and Kinetic Relations Holding in the Halogen Abstraction from Organohalogen Compounds by Alkyl Radicals

2005

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The relative rate constants were determined, and the absolute rate constants were estimated, for halogen transfer from N,N-dihaloarenesulfonamides, (dichloroiodo)arenes, benzyl bromides, and arenesulfonyl chlorides to cyclohexyl radical and from N,N-dihaloarenesulfonamides to benzyl radical. Polar effect of the substituent was found to be the main factor determining the rate of halogen transfer from benzyl bromides and arenesulfonyl chlorides; it increases with rise in the electrophilicity of the organohalogen substrate due mainly to charge distribution in the transition state.While considering the relations between the structure of organic molecules and the rate of radical transfer of hydrogen, the main factor is the heat effect of the hydrogen transfer stage, and its rate increases in parallel with the exothermic effect. In keeping with the Bell EvansPolanyi principle, in most cases the rate of transfer of an atom is linearly related to the heat effect. Exceptions are possible when a radical to which an atom is transferred possesses pronounced electrophilic or nucleophilic properties. In terms of the model based on the Marcus equation, increase in the electrophilicity or nucleophilicity of a radical leads to change of the internal reaction barrier as a result of charge separation in the transition state [1]. For example, the rate of abstraction of a hydrogen atom by chlorine and some other electrophilic radical species depends on polar effects of substituents in the substrate to a greater extent than on the heat effect. On the other hand, general relations holding in halogen transfer to alkyl radicals have been studied poorly. Therefore, we examined the effect of the structure of organic halogen compounds on the rate of halogen transfer therefrom to alkyl radicals.We determined the relative rate constants for abstraction of chlorine and bromine atoms from halogenating agents and arenesulfonyl chlorides by cyclohexyl and benzyl radical, following the procedure developed previDeceased.ously [2]. This procedure is based on competing abstraction of halogen from reagents XHlg 1 and YHlg 2 by alkyl radicals generated by radical chain halogenation of the corresponding alkane under conditions excluding formation of molecular halogen. Using the absolute rate constant for bromine transfer from N-bromosuccinimide (NBS) to benzyl radical, k(NBS) = (5.0 ± 0.3) 1 0 5 l mol 1 s 1 [3], we estimated the absolute rate constants of halogen transfer in the examined reactions. The relative and absolute rate constants are given in Table 1.

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“…a-Bromo-a-fluorotoluene was synthesized by the procedure described in [25]. Activated lead was prepared according to [15].…”

Section: Methodsmentioning

confidence: 99%

Reaction of Fluoro(phenyl)carbene with Schiff Bases: Synthesis of 2-Fluoro-2-phenylaziridines

2005

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Fluoro(phenyl)carbene generated by reaction of =-bromo-=-fluorotoluene with potassium tertbutoxide reacts with Schiff bases to afford the corresponding 2-fluoro-2-phenylaziridines. The latter were isolated in low yields due to their instability under the carbene generation conditions. Although the reaction of =,=-dibromo-=-fluorotoluene with zinc and lead involves formation of fluoro(phenyl)carbene, this procedure is not suitable for the synthesis of 2-fluoro-2-phenylaziridines.

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Cited by 6 publications

References 11 publications

High Turnover Remote Catalytic Oxygenation of Alkyl Groups: How Steric Exclusion of Unbound Substrate Contributes to High Molecular Recognition Selectivity

High Turnover Remote Catalytic Oxygenation of Alkyl Groups: How Steric Exclusion of Unbound Substrate Contributes to High Molecular Recognition Selectivity

Structural and Kinetic Relations Holding in the Halogen Abstraction from Organohalogen Compounds by Alkyl Radicals

Reaction of Fluoro(phenyl)carbene with Schiff Bases: Synthesis of 2-Fluoro-2-phenylaziridines

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