Conjugate Addition Of Dialkylzinc Research Articles

Copper–Bis(NHC)-Catalyzed Asymmetric Conjugate Addition of Dialkylzincs to Enones

Copper–Bis(NHC)-Catalyzed Asymmetric Conjugate Addition of Dialkylzincs to Enones

ChemInform Abstract: Re‐Evaluating the Nucleophilicity of Zinc Enolates in Alkylation Reactions.

AbstractThe allylic and benzylic alkylation of zinc enolates, generated by asymmetric copper‐catalyzed conjugate addition of dialkylzinc (II) towards cyclic enones (I), with various electrophiles is described.

Re‐Evaluating the Nucleophilicity of Zinc Enolates in Alkylation Reactions

AbstractThe use of toluene allows for allylic and benzylic alkylation of zinc enolates, derived from an asymmetric copper‐catalyzed conjugate addition of dialkylzinc, using a range of valuable electrophiles. The one‐pot procedure avoids the use of additional transition‐metal catalysts and does not require highly activated electrophiles.

One-Pot Asymmetric Conjugate Addition−Trapping of Zinc Enolates by Activated Electrophiles

The copper-catalyzed asymmetric conjugate addition of dialkyl zinc leads to homochiral zinc enolates. These intermediates were trapped in situ with activated allylic electrophiles, without the need of additional palladium catalysis. High trans selectivity (85/15 to 100/0) and excellent enantioselectivities (up to 99%) could be attained. The functionalized nature of the electrophiles makes the new synthons potential candidates for further elaboration.

Discovery of a new efficient chiral ligand for copper-catalyzed enantioselective Michael additions by high-throughput screening of a parallel library.

A combinatorial library of 125 chiral Schiff base ligands 5 was synthesized with the use of solution-phase parallel synthesis and solid-phase extraction (SPE) techniques to scavenge excess reagents and reaction by-products and avoid chromatography. The synthetic methodology coupled five N-Boc-protected beta-amino sulfonyl chlorides 1a-e with five different amines 2f-j to give 25 N-Boc sulfonamides 3, which were in turn deprotected and coupled with five salicylaldehydes 4p-t to give 125 ligands 5 in good yields and of sufficient purity to be used in ligand-catalyzed reactions. These ligands were tested in the copper-catalyzed conjugate addition of dialkyl zinc to cyclic and acyclic enones. A multisubstrate high-throughput screening of the library was performed with an equimolar mixture of 2-cyclohexenone and 2-cycloheptenone (9 and 10, respectively, 0.2 mmol total), with 5.5 mol% ligand 5 (0.011 mmol) and 5 mol% Cu(OTf)2 (OTf= OSO2CF3) (0.010 mmol) in 1:1 toluene/ hexane at - 20 degrees C. From the screening of the library, 5bhr was identified as the best ligand, which yielded 3-ethylcyclohexanone (12) and 3-ethylcycloheptanone (13) in 82% and 81% ee, respectively, and complete conversions. Under optimized conditions (2.75 mol% 5bhr, 2.5 mol% copper(i) triflate, toluene as reaction solvent), improved results were obtained for 12 (90% ee, 93% yield) and for 13 (91% ee, 95% yield). Selected ligands 5 were also tested in the addition of Me2Zn to 2-cyclohexenone (9, ee up to 79%), of Et2Zn to 2-cyclopentenone (11, ee up to 80%) and to acyclic enones 16 and 17 (ee up to 50%).

Novel Biphenol Phosphoramidite Ligands for the Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl zincs

Phosphoramidite ligands, based on a chiral amine and atropoisomerically flexible biphenols, induce high enantioselectivities (ee's up to 98%) in the copper-catalyzed conjugate addition of dialkyl zinc reagents to a variety of Michael acceptors.

ChemInform Abstract: Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl Zinc to Nitro-Olefins.

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ChemInform Abstract: Design and Synthesis of the Chiral Ligands for the Highly Enantioselective Asymmetric Reactions of Carbonyl Compounds

Several chiral ligands were designed and synthesized which perform highly enantioselective asymmetric reactions of carbonyl compounds. Enantioselective reduction of ketones with lithium borohydride modified with N, N'-dibenzoylcystine (or N-benzoylcystein) and tent-butyl alcohol (or ethanol) provided optically active sec.-alcohols in up to 9293% e.e. Functionalized ketones such as α-, β- haloketones, α- and β-aminoketones, pyridyl ketones, and fl-ketoesters were also reduced enantioselectively to afford opticall active epoxides, oxetanes, aminoalcohols, pyridyl alcohols, and β-hydroxyesters in high e.e.'s. Chiral pyrrolidinylmethanols, N, N-dibutylnorephedrine (DBNE), chiral piperazine, and polymer bound N-alkylnorephedrine were efficient chiral catalysts of the enantioselective addition of dialkyl zincs to aldehydes. Alkylation of both aliphatic and aryl aldehydes afforded optically active sec-alcohols in high e.e.'s. Formylesters afforded optically active lactones. Enantioselective conjugate addition of dialkyl zincs to enones was catalyzed by chiral complex prepared from DBNE and Ni (acac) 2 or NiBr2.

カルボニル化合物の高エナンチオ選択的不斉反応を目的とする不斉配位子の設計と合成

Several chiral ligands were designed and synthesized which perform highly enantioselective asymmetric reactions of carbonyl compounds. Enantioselective reduction of ketones with lithium borohydride modified with N, N'-dibenzoylcystine (or N-benzoylcystein) and tent-butyl alcohol (or ethanol) provided optically active sec.-alcohols in up to 9293% e.e. Functionalized ketones such as α-, β- haloketones, α- and β-aminoketones, pyridyl ketones, and fl-ketoesters were also reduced enantioselectively to afford opticall active epoxides, oxetanes, aminoalcohols, pyridyl alcohols, and β-hydroxyesters in high e.e.'s. Chiral pyrrolidinylmethanols, N, N-dibutylnorephedrine (DBNE), chiral piperazine, and polymer bound N-alkylnorephedrine were efficient chiral catalysts of the enantioselective addition of dialkyl zincs to aldehydes. Alkylation of both aliphatic and aryl aldehydes afforded optically active sec-alcohols in high e.e.'s. Formylesters afforded optically active lactones. Enantioselective conjugate addition of dialkyl zincs to enones was catalyzed by chiral complex prepared from DBNE and Ni (acac) 2 or NiBr2.