- Phosphabarrelenes as ligands in rhodium-catalyzed hydroformylation of internal alkenes essentially free of alkene isomerization
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Despite significant research efforts in the past, one of the remaining problems to be solved in industrially important hydroformylation is the chemoselective low-pressure hydroformylation of internal alkenes. We report here on a new class of phosphabarrelene/rhodium catalysts 2 that display very high activity towards hydroformylation of internal alkenes with an unusually low tendency towards alkene isomerization. Preparation of new phosphabarrelene ligands, studies of their coordination properties, as well as results obtained in the rhodium-catalyzed hydroformylation of cyclic and acyclic internal alkenes are reported.
- Fuchs, Evelyn,Keller, Manfred,Breit, Bernhard
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p. 6930 - 6939
(2007/10/03)
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- B-alkylcatecholboranes as a source of radicals for efficient conjugate additions to unsaturated ketones and aldehydes
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Selective and efficient generation of alkyl radicals from alkenes as well as their addition to unsaturated ketones and aldehydes is reported. The method is based on a simple one-pot procedure involving the hydroboration of the alkene with catecholborane, followed by treatment with a catalytic amount of oxygen in the presence of DMPU and a radical trap. Examples of cyclization and cascade reactions are reported.
- Ollivier, Cyril,Renaud, Philippe
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p. 1468 - 1473
(2007/10/03)
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- TRIS(TRIMETHYLSILYL)SILANE AS MEDIATOR IN ORGANIC SYNTHESIS VIA RADICALS
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Silane 3 is an effective mediator in organic synthesis via radicals.Reactions with this silane give smaller amounts of unwanted reduction products than reactions with toxic stannanes.
- Giese, Bernd,Kopping, Birgit,Chatgilialoglu, Chryssostomos
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p. 681 - 684
(2007/10/02)
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- Synthesis of aldehydes and products of such synthesis
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The disclosure describes the production of complex aliphatic, unsaturated and cycloalkane aldehydes utilizing heterocyclic ring compounds, such as oxazines, particularly dihydro-1,3-oxazines. The oxazines are treated with an alkali metal-alkane compound, such as butyl lithium in the presence of an organic solvent at subzero temperature to form an anion of the oxazine. This anion is then alkylated in the anhydrous reaction mixture by introduction of a suitable halide, epoxide or ketone while still at a subzero temperature and mixture is permitted to warm up to room temperature, following which the reaction mixture is acidified, as with hydrochloric acid to pH 2 to 3, extracted and then made basic, as with caustic alkali with cooling. The reaction mixture is then extracted, as with ether, to produce after evaporation the alkylated dihydro-1,3-oxazine. The alkylated dihydro-1,3-oxazine is then reacted with an alkali metal or sodium borohydride or borodeuteride or borotritide, with cooling to subzero temperatures at about a neutral pH and then transferred into a basic aqueous environment following extraction of the aqueous layer with an organic solvent, such as ether, to give a tetrahydro-1,3-oxazine. This compound may then be converted to the aldehyde desired by steam distillation or by hydrolysis in the presence of a dilute or weak acid, such as hydrochloric or oxalic acid. The aldehydes may then be extracted. These aldehydes are useful as components or intermediates in flavoring or perfumes, in insect attractants and repellants, and in pharmaceuticals.
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