28895-03-6Relevant articles and documents
Hydrogen Atoms as Convenient Synthetic Reagents: Mercury-Photosensitized Dimerization of Functionalized Organic Compounds in the Presence of H2
Muedas, Cesar A.,Ferguson, Richard R.,Brown, Stephen H.,Crabtree, Robert H.
, p. 2233 - 2242 (2007/10/02)
Hydrogen atoms are generated by mercury photosensitization in an unexceptional apparatus that makes them readily available for organic chemistry on a preparatively useful scale at 1 atm of pressure and temperatures from 0-150 °C. The H atoms add to CH2=CH-CH2X to give the intermediate radical CH3-(?CH)-CH2X, which dimerizes to give CH3CH(CH2X)-CH(CH2X)CH3. The saturated substrates CH3CH2CH2X undergo H abstraction to give CH3CH2(?CH)X as intermediates and CH3CH2CH(X)-CH(X)CH2CH3 as final products. The reaction shows a tolerance for different functional groups, X, which may be an alkyl or fluoroalkyl chain or contain vinyl, epoxy, ester, ketone, nitrile, and silyl groups. Radical disproportionation products are also formed but are easily separated. H atoms attack the weakest C-H bonds of the substrates with high selectivity. In our earliest direct mercury photosensitization, Hg* often failed to attack the substrate C-H bonds to give dimers; the presence of H2 strongly suppresses direct Hg* chemistry. H atoms are not sensitive to steric or polar effects Radical fragmentation is avoided by using "high" pressures (1 atm). Intramolecular radical additions to C=C bonds and methyl group 1,2-shift were also seen in some cases. Exceptional product ratios are observed for cross-reactions involving hydroxyalkyl radicals where H-bonding favors the homodimers in certain cases. Several bond strengths of C-H bonds α to CO were determined: EtCO2Me, 94.5; i-PrCO2Me, 92.7; cyclopentanone, 94.3; (i-Pr)2CO, 91.9 kcal/mol.
DEHYDRODIMERIZATION OF KETONES, CARBOXYLIC ACIDS, AMIDES, ESTERS, ALCOHOLS, AND AMINES, VIA MERCURY-PHOTOSENSITIZATION
Boojamra, Constantine G.,Crabtree, Robert H.,Ferguson, Richard R.,Muedas, Cesar A.
, p. 5583 - 5586 (2007/10/02)
Selective dehydrodimerization of the title compounds can be carried out on a preparative scale at 1 atm. and at 25-110 deg C in a simple apparatus by Hg-photosensitized reaction under H2.
Selectivity of Radical Formation in the Reaction of Carbonyl Compounds with Manganese(III) Acetate
Midgley, Gary,Thomas, C. Barry
, p. 1103 - 1108 (2007/10/02)
The selectivity of radical generation in the oxidation of carbonyl compounds by manganese(III) has been studied in two ways.Competitive reaction of acetic and propionic acids under conditions in which the resultant radicals are trapped efficiently by an alkene suggests that propionic acid reacts some 3.8 times more readily than does acetic acid.Oxidation of butanone under similar conditions gives products in the formation of which reaction has occurred 2.9 times more readily at C-3 of butanone than at C-1.However, this ratio reflects a combination of chain propagation and of initiation by manganese(III) oxidation.When propagation is effectively eliminated, the C-1 position is the more reactive.The significance of these observations on the mechanism of oxidation of carbonyl compounds by manganese(III) is discussed.It is suggested that enol radical-cations can be formed in the reaction but that these do not give carbonyl-stabilised radicals by deprotonation.
TETRAHALOBENZENES AS DI-ARYNE EQUIVALENTS IN POLYCYCLIC ARENE SYNTHESIS
Hart, Harold,Lai, Chung-yin,Nwokogu, Godson Chukuemaka,Shamouilian, Shamouil
, p. 5203 - 5224 (2007/10/02)
1,2,4,5-Tetrabromobenzenes and analogous naphthalenes react with one or two equivalents of n-butyllithium and various dienes (furans, pyroles, cyclopentadienes, fulvenes) to form mono- or bis-cycloadducts.Highly substituted arenes can be obtained by removing the oxygen or nitrogen bridges from the furan or pyrrole adducts.By choice of conditions, two identical or two different rings can be fused to the di-aryne equivalent.Improved short syntheses of permethylnaphthalene, -anthracene and -naphthacene are described.A new triphenylene synthesis is presented.
Oxydation anodique de β-cetocarboxylates en milieu aqueux ou hydroorganique. Application a la synthese de γ-dicetones, de cetones ethyleniques et de cetoamides
Chkir, Moncef,Lelandais, Daniel,Bacquet, Cathy
, p. 945 - 951 (2007/10/02)
A systematic study of the anodic oxidation of β-ketocarboxylate anions in aqueous or hydroorganic solvents allows to distinguish the factors directing this reaction.Thus, it is possible by the appropriate choice of reaction medium and structure of the starting ion to synthesize products such as γ diketones, ethylenic ketones and ketoamides.
