ABSTRACT
[reaction: see text] The value of arylboranes as precursors for arylzinc reagents in asymmetric catalysis is demonstrated. Kinetic studies on the transmetalation reaction with zinc reagents rationalize the observed differences of three classes of arylboranes in catalytic applications. By using the stable and easily accessible triarylborane ammonia complexes, an array of chiral diarylmethanols in high yield and enantioselectivity was synthesized.
Subject(s)
Benzyl Alcohols/chemical synthesis , Boranes/chemistry , Organometallic Compounds/chemistry , Quaternary Ammonium Compounds/chemistry , Zinc/chemistry , Benzyl Alcohols/chemistry , Catalysis , Molecular StructureABSTRACT
Various new diazonium ions on a polymeric support that have a variety of counterions and complexation with crown ethers have been prepared, and the thermal stability of these resins over a larger temperature interval has been investigated. Nonisothermal kinetics applied to DSC data have been used predicting the lifetime of the resins.
ABSTRACT
[reaction: see text] [2.2]Paracyclophane-based ketimine ligands were evaluated as catalysts for the enantioselective addition of in situ-prepared alkynylzinc reagents to aldehydes. The initial high activity and enantioselectivity of these ligands could be improved by an additive screening. The final protocol gives chiral propargyl alcohols in up to >98% ee.
ABSTRACT
The efficient esterification of various sulfonic acids and sulfonates using polymer-bound triazenes based on the triazene T2 linker is described. Esterification of enantiopure alpha-substituted sodium sulfonates was performed in the presence of an alkylating resin without racemization. Racemization is a serious drawback in the esterification route via sulfonyl chlorides because of intermediate sulfene formation. To demonstrate the versatility of this protocol, phosphoric and phosphinic acids have been converted into the corresponding esters as well. All products were obtained in good yield and excellent purities without any further purification steps.
ABSTRACT
The application of planar and central chiral [2.2]paracyclophane-based N,O-ligands in asymmetric diethylzinc additions to various aldehydes is described revealing an unusual substrate spectrum for the catalysts and their remarkably high activity.
ABSTRACT
A range of di- and tri-substituted triazenes have been synthesized from a polymer-supported diazonium salt and various primary and secondary amines. The triazenes obtained were treated with transition metal salts to form polymer-supported metal complexes in firstly a general screen and then in a specific manner.
Subject(s)
Palladium/chemistry , Polymers/chemistry , Ruthenium/chemistry , Triazenes/chemistry , Amines/chemistry , Catalysis , Chemistry, Organic/methods , Combinatorial Chemistry Techniques , Diazonium Compounds/chemistry , Ligands , Organometallic Compounds/chemical synthesis , Organometallic Compounds/chemistry , Triazenes/chemical synthesisABSTRACT
A range of polymer-supported triazenes and their metal-bound analogues were screened for use in catalysis. Fe, Cu and Zr complexes were, together with the polymer-supported triazene ligand alone, screened in the addition of Et(2)Zn to benzaldehyde. A supported Pd triazene complex was screened for activity in Suzuki and Sonogashira reactions and a supported Ru triazene complex screened for transfer hydrogenation.
Subject(s)
Organometallic Compounds/chemistry , Polymers/chemistry , Triazenes/chemistry , Amines/chemistry , Benzaldehydes/chemistry , Catalysis , Chemistry, Organic/methods , Diazonium Compounds/chemistry , Hydrogenation , Indicators and Reagents , Ligands , Metals, Heavy/chemistry , Stereoisomerism , Triazenes/chemical synthesisABSTRACT
The first highly enantioselective dialkylzinc addition to imines in the presence of catalytic amounts of N,O-ligands is reported. N-formyl-alpha-(p-tolysulfonyl)benzylamines are the readily available starting materials easily obtained in a one-pot synthesis from benzaldehydes, formamide, and p-tolylsulfinic acid. Upon deprotonation, the sulfinate is eliminated to give the acyl imine. The acyl imines further react with alkylzinc reagents in the presence of catalytic amounts of [2.2]paracyclophane-based N,O-ligands L yielding the alkylated N-(1-phenylpropyl)formamides with excellent yields and enantioselectivities.
