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Paul Knochel

Publications and source records attributed to Paul Knochel.

At least 37 records · Page 2Linked to original sources
PubMed2005

Efficient cross-coupling of functionalized arylzinc halides catalyzed by a nickel chloride-diethyl phosphite system.

[reaction: see text] The combination of diethyl phosphite and DMAP as ligands for nickel in an 8:1 THF-N-ethylpyrrolidinone (NEP) mixture allows a very efficient cross-coupling reaction to be performed between various functionalized arylzinc halides and aryl bromides, triflates and activated chlorides. The reaction proceeds at 25 degrees C within 1-48 h and requires only 0.05 mol % of the nickel catalyst.

Journal Article↗
PubMed2005

Functionalized magnesium organometallics as versatile intermediates for the synthesis of polyfunctional heterocycles.

In the last few years, we have demonstrated that the halogen/magnesium-exchange reaction is a unique method for preparing a variety of new functionalized aryl, alkenyl, heteroaryl magnesium compounds which has considerably extended the range of functionalized Grignard reagents available for synthetic purposes. A variety of functional groups such as an ester, nitrile, iodide, imine and even sensitive groups like nitro, hydroxyl and boronic ester can be tolerated in these organomagnesium compounds. We wish to describe the application of this halogen/magnesium-exchange reaction for the preparation of a broad range of five- and six-membered functionalized heteroaryl magnesium compounds and their reactions with various electrophiles providing a new entry to a range of polyfunctional heterocycles such as thiophene, furan, pyrrole, imidazole, thiazole, antipyrine, pyridine, quinoline and uracil derivatives.

Antipyrine↗
PubMed2005

Stereoselective functionalization of cyclopropane derivatives using bromine/magnesium and sulfoxide/magnesium exchange reactions.

The reaction of 2,2-dibromo-1-methyl-cyclopropanecarbonitrile (1) with i-PrMgCl in Et(2)O/CH(2)Cl(2) provides the cis-magnesium-carbenoid (2), which reacts with high retention of configuration with various electrophiles. If E = SPh, a stereoselective generation of a quaternary center via a sequential Br/Mg- and sulfoxide/Mg-exchange can be achieved. [reaction: see text]

Journal Article↗
PubMed2005

Preparation of polyfunctional arylmagnesium reagents bearing a triazene moiety. A new carbazole synthesis.

[reaction: see text] The reaction of iodo- or bromo-substituted aryltriazenes with i-PrMgCl.LiCl generates the corresponding magnesiated derivatives which react with various electrophiles (acid chlorides, 3-iodoenones, allylic halides, aldehydes) affording polyfunctional triazenes. They can be readily converted to the corresponding polyfunctional aryl iodides. This new synthetic strategy was applied to prepare functionalized carbazoles.

Journal Article↗
PubMed2005

Synthesis of functionalized nitroarylmagnesium halides via an iodine-magnesium exchange.

[reaction: see text] Various nitro-substituted aryl and heteroaryl iodides undergo an iodine-magnesium exchange reaction when treated with PhMgCl leading to nitro-containing magnesium organometallics. These Grignard reagents display an excellent stability at temperatures below -40 degrees C and do not undergo electron-transfer reactions. They react as expected with various electrophiles.

Journal Article↗
PubMed2005

Metalated nitriles: organolithium, -magnesium, and -copper exchange of alpha-halonitriles.

[reaction: see text] alpha-Halonitriles react with alkyllithium, organomagnesium, and lithium dimethylcuprate reagents generating reactive, metalated nitriles. The rapid halogen-metal exchange with alkyllithium and Grignard reagents allows selective exchange in the presence of reactive carbonyl electrophiles, including aldehydes, providing a high-yielding alkylation protocol. Lithiated and magnesiated nitriles react with propargyl bromide by S(N)2 displacement whereas organocopper nitriles react by S(N)2' displacement, correlating with the formation of a C-metalated nitrile.

Copper↗
PubMed2004

Preparation of cyclic alkenylmagnesium reagents via an iodine/magnesium exchange.

The reaction of various cyclic alkenyl iodides with i-PrMgCl.LiCl produces the corresponding alkenylmagnesium reagents under mild conditions. After reaction with various electrophiles, like allylic halides, disulfides, aldehydes and acid chlorides, the expected products are obtained in 53-91% yield. Remarkably, the mild conditions of the I/Mg-exchange tolerate the presence of sensitive diene functionalities.

Journal Article↗
PubMed2004

Stereoselective preparation of functionalized acyclic alkenylmagnesium reagents using i-PrMgCl.LiCl.

Acyclic functionalized alkenyl iodides are converted with high stereoselectivity to the corresponding functionalized alkenylmagnesium derivatives by the reaction with i-PrMgCl.LiCl between -40 and -20 degrees C. Functional groups such as a nitrile, chloride, iodide, and ester are readily tolerated. The conversion of an alkenyl iodide bearing a keto group to the corresponding silylated cyanohydrin allows preparation of the corresponding Grignard reagent affording, after acylation and deprotection, unsaturated 1,4-diketones.

Journal Article↗