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Paul Knochel

Publications and source records attributed to Paul Knochel.

At least 19 recordsLinked to original sources
PubMed2007

The Mg-oppenauer oxidation as a mild method for the synthesis of aryl and metallocenyl ketones.

Magnesium alkoxides undergo a hydride-transfer oxidation with benzaldehyde as the oxidant. This magnesium variant of the Oppenauer oxidation was used for the synthesis of polyfunctional biaryl ketones. LiCl was found to promote this reaction by enhancing the solubility of magnesium alkoxides. This mild oxidation method was especially useful for preparing ketones bearing a metallocenyl unit as well as various new ferrocenyl ketones and tricarbonylchromium complexes. This last class of ketones was reduced with the CBS catalyst (CBS=Corey-Bakshi-Shibata, diphenyl oxazaborolidine) to chiral benzhydrol complexes with high enantioselectivity enabling an asymmetric synthesis of electron-rich or -poor benzhydryl alcohols (up to 94 % ee).

Alcohols↗
PubMed2006

Synthesis of functionalized diarylmethanes via a copper-catalyzed cross-coupling of arylmagnesium reagents with benzylic phosphates.

A combination of copper chloride, triethyl phosphite, and tetrabutylammonium iodide is a very efficient catalytic system for the synthesis of polyfunctionalized diarylmethanes, using the cross-coupling reaction of arylmagnesium halides with benzylic phosphates. The antibiotic Trimethoprim has been prepared using this Cu(I)-catalyzed cross-coupling in 52% overall yield (four steps).

Journal Article↗
PubMed2006

Practical highly enantioselective synthesis of propargylamines through a copper-catalyzed one-pot three-component condensation reaction.

The one-pot three-component reaction of terminal alkynes, aldehydes and secondary amines in the presence of copper(I) bromide/quinap is reported. The reaction scope has been determined and a broad variety of all three components has been used, which afforded the corresponding propargylamines in good to excellent yields and moderate to very good enantioselectivities. The reaction showed a strong positive nonlinear effect. The transformation of a propargylamine intermediate into the alkaloid (S)-(+)-coniine has also been described.

Aldehydes↗
PubMed2006

Stereoselective functionalization of beta-iodo-alpha,beta-unsaturated ketones via an iodine-copper exchange reaction.

[reaction: see text] Beta-iodo-alpha,beta-unsaturated carbonyl compounds undergo a stereoselective iodine-copper exchange reaction with (Nphyl)(2)CuLi, providing the corresponding alkenyl cuprates with retention of the double bond configuration. No competitive addition/elimination was observed, and the resulting cuprates were successfully functionalized with various electrophiles.

Journal Article↗
PubMed2006

Selective functionalization of imidazoles via an iodine-copper exchange reaction.

The reaction of protected 4,5-diiodoimidazoles with (PhMe2CCH2)2CuLi regioselectively provides 5-cuprated imidazoles, which readily react with various electrophiles furnishing functionalized imidazoles in good yields; remarkably, these resulting mono-iodoimidazoles undergo again an iodine-copper exchange reaction in the presence of sensitive functional groups, like an aldehyde or a ketone.

Copper↗
PubMed2006

Magnesiated unsaturated silylated cyanohydrins as synthetic equivalents of aromatic and heterocyclic grignard reagents bearing a ketone or an aldehyde.

[reaction: see text] The preparation of iodo-substituted aryl, heteroaryl, or cycloalkenyl ketones as silylated cyanohydrins allows the smooth performance of an I/Mg-exchange using i-PrMgCl.LiCl. A facile deprotection of the resulting functionalized products obtained by a reaction with electrophiles (acid chlorides, allylic bromide, benzylidene-p-toluenesulfonamide, and 3-iodocyclohexenone) produces polyfunctional ketones in good overall yields. This sequence can be extended to aromatic iodoaldehydes. In these cases, the deprotection of the silylated cyanohydrin functionality is best performed with aqueous CuSO(4) under basic conditions.

Journal Article↗
PubMed2006

Cobalt(II)-catalyzed cross-coupling between polyfunctional arylcopper reagents and aryl fluorides or tosylates.

[reaction: see text] Organocopper compounds prepared by the transmetalation of functionalized arylmagnesium halides with CuCN.2LiCl undergo smooth cross-coupling reactions with aryl fluorides and tosylates bearing a carbonyl function in the ortho position in the presence of Co(acac)(2) (7.5 mol %), Bu(4)NI (1 equiv), and 4-fluorostyrene (20 mol %) as promoters in DME/THF/DMPU leading to polyfunctional aromatics or heterocycles.

Journal Article↗