630-17-1Relevant articles and documents
The Walling, El-Taliawi, and Zhao "Carnonyl Effect" in Radical Brominations Is an Example of HBr Reversal. It Is Not Relevant to ? and ? Radical Chemistry.
Skell, P. S.
, p. 1838 - 1840 (1984)
Walling, El-Taliawi, and Zhao claim that our "S? chemistry" is reproduced in photobrominations employing Br2 in the presence of carbonyl compounds (no NBS).Photobromination of alkanes by N-bromosuccinimide (NBS) shows selectivities that vary, but which show limiting values for significant ranges of rection conditions.We have attributed these different limiting values to three reaction paths which differ in involving either Br., S?, or S? as the intermediate hydrogen-abstracting radical.Walling, El-Taliawi, and Zhao (WEZ) have reported selectivities they belive are attributable to a carbonyl-bromine intermediate rather than our S?.Evidence is now presented to show that the WEZ results are due to HBr in varying amounts with or without carbonyl compounds present.This represents a fourth type of selectivity and one that is sensitive to HBr concentrations and probably arises in their systems from the following reaction: There is no carbonyl effect.This fourth type had been deliberately excluded from our work, so that reactions involving HBr reversal are not relevant to our published work on succinimidyl chemistry.Thus, the selectivities (per H basis) for the neopentane/methylene chloride competitions stand without modification, as published earlier: 0.067, 1.0 and 17 for B., S?, and S?, respectively.
Radical Chain Carriers in N-Bromosuccinimide Brominations
Walling, Cheves,El-Taliawi, Gamil M.,Zhao, Chengxue
, p. 5119 - 5124 (1983)
Relative reactivities per hydrogen (r's) for neopentane-CH2Cl2 have been redetermined for photobromination by Br2, r = 0.03-0.4, NBS + Br2, r = 1-2.5, and NBS + 1,1-dichloroethylene (DCE) as a Br. trap, r > 20.In the last case β-bromopropionyl isocyanate (BPI) is the major product.In Br2 reactions r's vary with experimental conditions and are increased significantly by a number of carbonyl and succinimide derivatives.BPI is also a major product in the brominaton of CHCl3 in the presence of DCE and in the UV photolysis of NBS in CD2Cl2 even in the presence of Br2.For CH2Cl2-CD2Cl2 mixtures, kH/kD ca. 10 for both NBS-Br2 and NBS-DCE systems.The kinetics of decomposition of NBS in CH2Cl2 in the presence of Br2, initiated by UV light, azobis(isobutyronitrile) and benzoyl peroxide are zero order in NBS, with k for attack of the chain-carrying radical on CH2Cl2 estimated as 55 at 50 deg C.In the presence of DCE, benzoyl peroxide initiated reactions in CH2Cl2 are also zero order, with rates corresponding to a rate constant for ring opening kd ca. 1660.Addition of cyclohexane produces an unexpected increase in rate corresponding to kd ca. 1.5*104, and k for reacton of the succinimide radical with cyclohexane ca. 104.If these rate constants are valid, they require a radical lifetime of ca. 10-4 s, and this and their low value appear inconsistent with a high-energy excited state of the succinimide radical.It is proposed that the chain carrier in the NBS-Br2 system is a reaction product of NBS and a bromine atom, for which some possible structures are suggested.
Tandem cyclopropanation with dibromomethane under Grignard conditions
Brunner, Gerhard,Eberhard, Laura,Oetiker, Juerg,Schroeder, Fridtjof
, p. 7543 - 7554 (2008/12/22)
(Chemical Equation Presented) Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and CH 2Br2 under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from α-substituted substrates, which are in accord with a staggered Houk model. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropyl carbinols.
Scavenger assisted combinatorial process for preparing libraries of tertiary amine compounds
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, (2008/06/13)
This invention relates to a novel solution phase process for the preparation of tertiary amine combinatorial libraries. These libraries have utility for drug discovery and are used to form wellplate components of novel assay kits.
PHOTOSTIMULATED REACTIONS OF NEOPENTYL IODIDES WITH CARBANIONS IN DMSO BY THE SRN1 MECHANISM
Penenory, Alicia B.,Rossi, Roberto A.
, p. 605 - 610 (2007/10/03)
Neopentyl iodide, 1, reacted under photostimulation with several carbanionic nucleophiles in DMSO.With acetone enolate ion only reduction and dimerization occured, but good yields of substitution products have been obtained with acetophenone, 5, and anthrone, 9, anions as nucleophiles.Nitromethane anion, 7, does not react with 1 under irradiation, but good yields of the substitution products are obtained when the photostimulated reaction is carried out in the presence of acetone enolate ions (entrainment reaction).Inhibition experiments by p-dinitrobenzene and by the radical trap TEMPO, suggest that these reactions occur by the SRN1 mechanism of nucleophilic substitution.The photostimulated reaction of 1,3-diiodo-2,2-dimethylpropane, 15, with 5 gave the disubstitution product 17 and the reduced monosubstitution product 18.It has been found that the monosubstitution product 16 (in which iodine is retained) is not an intermediate of these reactions. 1-iodoadamantane, 12, is more reactive (ca. 4.9 times) than 1 in competitive experiments toward 5 and under photostimulation.
Preparation and properties of metallacyclobutanes of nickel and palladium
Miyashita, Akira,Ohyoshi, Mayumi,Shitara, Hiroaki,Nohira, Hiroyuki
, p. 103 - 112 (2007/10/02)
Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes.Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carb
SELECTIVE HYDROBROMINATION OF BRANCHED ALCOHOLS USING PHASE TRANSFER CATALYSIS
Dakka, Gihad,Sasson, Yoel
, p. 1223 - 1224 (2007/10/02)
In the presence of quaternary ammonium phase transfer catalysts hydrobromination of branched alcohols proceed via selective SN2 mechanism practically without rearrangements.
Ground- and Excited-State Succinimidyl Radicals in Chain Reactions: A Reexamination
Skell, Philip, S.,Luening, Ulrich,McBain, Douglas S.,Tanko, James M.
, p. 121 - 127 (2007/10/02)
The succinimidyl radical chemistry reported earlier and previously attributed to the ? state is reproduced, leaving unsettled only its assignment to the ? and ? state.This chemistry, observed in the presence of small amounts of alkenes which scavenge bromine, includes the following: (1) additions to alkenes, (2) additions to arenes, (3) Cl-like substitution selectivities, and (4) ring-openings.The chemistry previously reported under the title "?" is neither as simple nor conclusive as thought earlier.As reported earlier, ring-opening is suppressed by inclusion of bromine, benzene, bromotrichloromethane, or larger amounts of alkenes.These observations indicate the presence of a different chain carrier, formerly labeled as S?.We show now that the S? explanation was not correct with addends benzene, bromotrichloromethane, and olefins, and we identify the specific competitive processes.Reactions in the presence of bromine still show evidence for a third hydrogen abstractor besides an imidyl radical and a bromine atom.At this time there is no unambiguous identification of this third chain intermediate.
REACTIONS OF BrCl WITH ALKYL RADICALS.
Skell, P. S.,Baxter, H. N.,Tanko, J. M.
, p. 5181 - 5184 (2007/10/02)
It is demonstrated that photohalogenation of low reactivity substrates with BrCl occurs mainly with Cl. selectivity.With tertiary or benzylic hydrogens in the substrate, mainly Br. selectivity is observed.These observations are rationalized, taking into account the relative concentrations of halogen atoms and their respective rates of hydrogen abstractions.The resultant radicals react with BrCl to make (RBr/RCl) in ratios between 1 and 15.
Electrophilic cleavages in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si, C). 1. Product distribution
Hawker, Darryl W.,Wells, Peter R.
, p. 821 - 825 (2008/10/08)
The extent to which Sn-CH2 and/or Sn-CH3 cleavage occurs in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si) in reactions with several electrophiles has been determined. With iodine and with