Enantioselective copper-catalyzed conjugate addition using chiral diaminocarbene ligands

Chiral diaminocarbene ligands, generated by in-situ deprotonation of the corresponding chiral imidazolinium salts, are shown to be efficient ligands in the asymmetric copper-catalyzed 1,4-conjugate addition of diethylzinc to enones, allowing enantiomeric excesses of up to 51% to be achieved.     

Mechanistic rationalization of organocatalyzed conjugate addition of linear aldehydes to nitro-olefins

Kinetic studies of the conjugate addition of propanal to nitrostyrene catalyzed by diarylprolinol ethers reveal that formation of the product iminium species is rate-determining and is promoted by both the reaction product and acid additives. The beneficial role of a dominant cyclobutane intermediate in maintaining high stereoselectivity is highlighted. This mechanistic understanding led to the design of highly productive reaction protocols.     

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to nitroalkenes

Copper-catalyzed asymmetric conjugate addition of diethylzinc to nitroalkenes using new chiral monodentate phosphoramidite ligands proceeds with high enantioselectivity up to 99% ee. [reaction: see text]     

Enantioselective conjugate radical addition to alpha'-hydroxy enones

Enantioselective conjugate radical addition to alpha'-hydroxy alpha,beta-unsaturated ketones, compounds containing bidentate donors, has been investigated. It has been found that radical additions to alpha'-hydroxy alpha,beta-unsaturated ketones in the presence of Mg(NTf2)2 and bisoxazoline ligand 5a proceeded cleanly, yielding the addition products in high chemical yields and good enantiomeric excesses.     

Enantioselective radical conjugate addition to alpha'-phosphoric enones

Catalytic enantioselective radical conjugate addition reactions using alpha'-phosphoric enone templates have been studied. The C 2-symmetric bisoxazoline-zinc(II) complex proves to be effective for high enantioselectivities and chemical yields. In addition, intermediate alpha-carbonyl alkyl radicals could be trapped with allyltributylstannane to afford anti-isomers as major products with high enantioselectivities.     

Enantioselective organocatalytic amine conjugate addition

The first enantioselective organocatalytic amine conjugate addition has been successfully developed. The application of LUMO-lowering iminium catalysis has enabled the highly chemo- and enantioselective 1,4-addition of a rationally designed N-silyloxycarbamate nucleophile (HOMO-raised) to alpha,beta-unsaturated aldehydes. Imidazolidinone 2*pTSA was found to catalyze the addition of various orthogonally N-protected silyloxycarbamate nucleophiles to a range of alpha,beta-unsaturated aldehydes, affording synthetically useful beta-amino aldehyde intermediates. The synthetic utility of the protocol was demonstrated in the rapid synthesis of enantioenriched beta-amino acids in one operation and 1,3-amino alcohol derivatives in three operations.     

Enantioselective organocatalytic conjugate addition of alpha-aminoketone to nitroolefins

The enantioselective organocatalytic conjugate addition of alpha-aminoketone to nitroolefins is reported.     

Enantioselective organocatalytic conjugate addition of aldehydes to nitrodienes

The asymmetric organocatalyzed Michael addition of aldehydes to alpha,beta-gamma,delta-unsaturated nitro compounds has been accomplished using only 5 mol % of (S)-diphenylprolinol silyl ether and 2 equiv of aldehyde in a mixture of ethanol and water (5% v/v). The Michael adducts were obtained in good yields, diastereoselectivities up to 94/6, and ee's up to 99%. This process provides synthetically useful compounds which can easily lead to more complex molecules, as exemplified with substituted tetrahydropyran or cyclohexene.     

Enantioselective palladium-catalysed conjugate addition of arylsiloxanes

The complex formed from Pd(CH(3)CN)(4)(BF(4))(2) and (R,R)-MeDUPHOS is a highly enantioselective catalyst for the asymmetric conjugate addition of aryltriethylsiloxanes to a variety of unsaturated ketones, lactones and lactams.     

Enantioselective conjugate addition of alkenylboronic acids to indole-appended enones

An enantioselective addition of alkenylboronic acids and alkynylboronic esters to unprotected indole-appended enones is reported. This transformation proceeds with high enantioselectivity and high product yields via the use of catalytic amounts of 3,3'-bis(pentafluorophenyl)-BINOL and Mg(Ot-Bu)(2). A range of α-branched indole derivatives are available from the transformation.     

Enantioselective organocatalytic conjugate addition of organoboron nucleophiles

This review covers the use of organoboron nucleophiles in enantioselective conjugate additions catalyzed by organic-based catalysts. It is divided into sections based on the type of nucleophile, with each section arranged in roughly chronological order. The categories of nucleophiles are alkynyl, alkenyl, and aryl boronates or borates. The principle modes of catalysis, iminium formation and boron chelation, are covered.     

Enantioselective Cu-catalyzed conjugate addition of diethylzinc to acyclic aliphatic enones

[reaction: see text] A new P-chiral phosphine bis(sulfonamide) ligand has been developed that allows the Cu-catalyzed enantioselective conjugate addition of Et(2)Zn to acyclic aliphatic enones. The reactions proceed with excellent levels of enantioselectivity (90-95% ee) with a range of enone substrates, involve the use of only 1.2 equiv of Et(2)Zn, and give best results at ambient temperature.     

Enantioselective conjugate addition of N,N-dialkylhydrazones to alpha-hydroxy enones

The activation of alpha-hydroxy enones by the Zn(OTf)2/tBuBOX catalyst enables the enantioselective conjugate addition of 1-methyleneaminopyrrolidine as a neutral d1 synthon. Experimental evidence supports a stereochemical model where a triflate ligand controls the geometry of the catalyst-substrate complex by means of a OH-OTf hydrogen bond. The synthesis of beta-cyano acids illustrates the potential of the methodology.     

Unprecedented copper-catalyzed asymmetric conjugate addition of organometallic reagents to alpha,beta-unsaturated lactams

For the first time, an excellent enantioselectivity has been obtained in the conjugate addition of hard organometallic reagents to alpha,beta-unsaturated lactams bearing appropriate protecting-activating groups on the nitrogen.     

Enantioselective Friedel-Crafts type addition of indoles to nitro-olefins using a chiral hydrogen-bonding catalyst--synthesis of optically active tetrahydro-beta-carbolines

The enantioselective Friedel-Crafts addition of indoles to nitro-olefins using chiral hydrogen-bonding bis-sulfonamides as the catalysts has been developed. The reactions, in the presence of only 2 mol% catalyst, generally proceed in high yields and with enantioselectivities up to 64% ee, and the enantiomeric excess can be improved to >98% ee by recrystallization. Various synthetic transformations of the Friedel-Crafts adducts are demonstrated: the nitro group can easily be reduced to the corresponding amine and the product obtained can undergo a stereocontrolled Pictet-Spengler cyclization to give, for example, enantiopure tetrahydro-beta-carbolines. The X-ray structure of the chiral bis-sulfonamides has been determined and based on these structures the mechanism for the stereoselectivity in the reaction is discussed.     

Aminohydroxyphosphine ligand for the copper-catalyzed enantioselective conjugate addition of organozinc reagents

An alanine-derived aminohydroxyphosphine ligand was developed for copper-catalyzed asymmetric conjugate addition of organozinc reagents to alpha,beta-unsaturated carbonyl compounds. This new tridentate ligand induces consistently high enantioselectivity in reactions of a variety of acyclic substrates. Theoretical mechanistic analysis suggests that the C-C bond formation takes place through a highly ordered transition state by the coordination of the phosphorus and nitrogen atoms to the copper(III) and zinc(II) atoms, respectively, and of the oxygen anion to both the metal centers.     

Biphenol-based phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of diethylzinc

Phosphoramidite ligands, based on ortho-substituted biphenols and a chiral amine, induce high enantioselectivities (ee's up to 99%) in the copper-catalyzed conjugate addition of dialkylzinc reagents to a variety of Michael acceptors. Particularly, the best reported ee's were obtained for acyclic nitroolefins.