Enantioselective sulfa-Michael addition of thioacids to α,β-unsaturated ketones with bifunctional organocatalyst

Organocatalytic conjugate addition of thioacids to α,β-unsaturated ketones has been studied in the presence of cinchona alkaloid derived urea catalyst. Both the enantiomers of products are accessible with the same level of enantioselectivity using pseudoenantiomeric quinine/quinidine derived catalysts. The catalytic process provides optically active thioesters with high chemical yields (up to 99%) and useful enantioselectivity (up to 83% ee). The reaction was performed with 1 mol % of catalyst in toluene at room temperature. A transition state model has been proposed to explain the stereochemical outcome of the reaction.     

Enantioselective aldol reactions of α,β-unsaturated ketones with trifluoroacetophenone catalyzed by a chiral primary amine

Chiral primary amine catalyzed direct asymmetric aldol reactions of ketones with trifluoroacetophenone, afforded trifluoromethylated β-hydroxycarbonyl aldol products bearing a quaternary carbon stereogenic center in high yields (up to 93% yield) and with high to excellent enantioselectivities of up to 99% ee.     

Asymmetric conjugate addition of malonate to α,β-unsaturated ketones in water using a perfluoroalkanesulfonamide organocatalyst

Perfluoroalkanesulfonamide organocatalyst 7 efficiently promotes asymmetric Michael additions of malonates to enones in cyclohexane or water to produce the corresponding addition products with excellent yields and with up to 99% ee.     

Asymmetric Michael addition of substituted rhodanines to α,β-unsaturated ketones catalyzed by bulky primary amines

A bulky group was introduced by design into a diamine catalyst, and a series of robust and tunable bulky chiral primary amine catalysts were developed and successfully applied in the direct conjugate addition of substituted rhodanines to α,β-unsaturated ketones. High yields (up to 99%) and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to 98% ee) were observed.     

Asymmetric aldol reactions of α,β-unsaturated ketoester substrates catalyzed by chiral diamines

Highly efficient asymmetric aldol reactions between α,β-unsaturated keto esters and acyclic ketones catalyzed by chiral diamines are reported. The corresponding products were obtained in excellent yields with excellent enantioselectivities. The absolute configuration for the product was determined by X-ray analysis. A variety of substrates were tolerable in the present catalytic system.     

Conjugate addition of unactivated thiols to α,β-unsaturated ketones catalyzed by a bifunctional rhenium(V)–oxo complex

ReOCl₃(OPPh₃)(S(CH₃)₂) has been found to be an efficient bifunctional catalyst for the 1,4-addition of thiols to α,β-unsaturated ketones. The addition of thiophenol derivatives and alkyl thiols proceeds under mild reaction conditions without pre-activation of the thiol or exogenous base. Reactions of aryl, alkyl, and cyclic enones produce the corresponding β-sulfanyl ketones in good to excellent yield.     

Asymmetric aldol addition of α-azido ketones to ethyl pyruvate mediated by a cinchona-based bifunctional urea catalyst

The first asymmetric synthesis of ethyl 4-aryl-3-azido-2-hydroxy-2-methyl-4-oxobutanoates via a cinchona organocatalyst induced aldol addition of α-azido ketones to ethyl pyruvate has been developed. The coupling reaction under optimized conditions was carried out to furnish tetrafunctionalized synthons with enantioselectivities of up to 91:9 and enriched diastereoselectivities of up to 95:5 (syn:anti).     

Highly diastereoselective and enantioselective Michael addition of 5H-oxazol-4-ones to α,β-unsaturated ketones catalyzed by a new bifunctional organocatalyst with broad substrate scope and applicability

A new thiourea-tertiary amine bifunctional catalyst derived from L-tert-leucine was developed and provides excellent stereocontrol in a novel and direct Michael addition of 5H-oxazol-4-ones to α,β-unsaturated ketones with much broad substrate scope. The conjugate addition products with chiral vicinal quaternary and tertiary stereocenters can be easily transformed to structurally interesting compounds or building blocks.     

Asymmetric Morita-Baylis-Hillman reactions catalyzed by chiral Brønsted acids

Chiral BINOL-derived Br?nsted acids catalyze the enantioselective asymmetric Morita-Baylis-Hillman (MBH) reaction of cyclohexenone with aldehydes. The asymmetric MBH reaction requires 2-20 mol % of the chiral Br?nsted acid 2e or 2f and triethylphosphine as the nucleophilic promoter. The reaction products are obtained in good yields (39-88%) and high enantioselectivities (67-96% ee). The Br?nsted-acid-catalyzed reaction is the first example of a highly enantioselective asymmetric MBH reaction of cyclohexenone with aldehydes.     

Enantioselective conjugate addition of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones catalyzed by chiral bifunctional organocatalysts

The catalytic enantioselective conjugate addition reaction of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones promoted by chiral bifunctional organocatalysts is described. The treatment of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones under mild reaction conditions afforded the corresponding Michael adducts with high enantioselectivity. The conjugate addition adducts are useful for the synthesis of chiral monofluoromethylated compounds.     

Asymmetric Michael addition of α-fluoro-α-phenylsulfonyl ketones to nitroolefins catalyzed by phenylalanine-based bifunctional thioureas

Phenylalanine-based bifunctional thiourea derivatives promoted the asymmetric Michael addition of α-fluoro-α-phenylsulfonyl ketones to nitroolefins, affording enantiomerically enriched fluorine-containing multifunctional molecules containing adjoining chiral fluorine-substituted quaternary and tertiary centers in good yields and enantioselectivities.     

Asymmetric Brønsted acid catalyzed carbonyl activation--organocatalytic domino electrocyclization-halogenation reaction

A highly efficient Br?nsted acid catalyzed enantioselective Nazarov cyclization-bromination reaction has been developed. The protocol gives access to highly functionalized trans-4,5-substituted 5-bromocyclopentenone derivatives in good yields and with excellent enantioselectivities.     

Asymmetric transfer hydrogenation of beta,gamma-alkynyl alpha-imino esters by a Brønsted acid

Asymmetric synthesis of trans-alkenyl alpha-amino esters was realized by chiral phosphoric acid catalyzed transfer hydrogenation of beta,gamma-alkynyl alpha-imino esters. Utilizing Hantzsch esters as the hydrogen donor, both the alkyne and imine moieties of beta,gamma-alkynyl alpha-imino esters were reduced to afford trans-alkenyl alpha-amino esters with up to 96% ee.     

An environmentally friendly Mukaiyama aldol reaction catalyzed by a strong Brønsted acid in solvent-free conditions

o-Benzenedisulfonimide, a new strong bench-stable Br?nsted acid, has been shown to efficiently catalyze the Mukaiyama aldol reaction of aldehydes or dimethyl acetals with silyl enol ethers under mild solvent-free reaction conditions.     

Reversal of chemoselectivity in Diels-Alder reaction with alpha,beta-unsaturated aldehydes and ketones catalyzed by Brønsted acid or Lewis acid

[reaction: see text] High chemoselectivity was observed in the Diels-Alder reaction of alpha,beta-unsaturated aldehyde and alpha,beta-unsaturated ketone with cyclopentadiene. Using Tf2NH as catalyst, the reaction gave Diels-Alder adduct derived from alpha,beta-unsaturated ketone as a major product. On the other hand, bulky Lewis acid, B(C6F5)3, gave mainly the cycloadduct of alpha,beta-unsaturated aldehyde and cyclopentadiene.     

Reaction of unsymmetrical α,β-unsaturated ketones with thiobarbituric acid

Carbocyclization of unsymmetrical 1,5-diarylpenta-1,4-dien-3-ones with thiobarbituric acid afforded previously unknown 7,11-diaryl-3-thioxo-2,4-diazaspiro[5.5]undecane-1,5,9-triones with high regio- and stereoselectivity. The same spiro compounds were also synthesized by three-component condensation of thiobarbituric acid with the corresponding aromatic aldehydes and 4-arylbut-3-en-2-ones.