John Cong Gui Zhao

A Homochiral Microporous Hydrogen-Bonded Organic Framework for Highly Enantioselective Separation of Secondary Alcohols

A homochiral microporous hydrogen-bonded organic framework (HOF-2) based on a BINOL derivative has been synthesized and structurally characterized to be a uninodal 6-connected {3(3)5(5)6(6)7} network. This new HOF exhibits not only a permanent porosity with the BET of 237.6 m(2) g(-1) but also, more importantly, a highly enantioselective separation of chiral secondary alcohols with ee value up to 92% for 1-phenylethanol.

Highly Diastereo‐ and Enantioselective Organocatalytic One‐Pot Sequential 1,4‐Addition/Dearomative‐Fluorination Transformation

Fluorination: A wide range of nitroolefins and pyrazol-5-ones undergo a sequential 1,4-addition/dearomative-fluorination transformation when treated with a catalytic amount of a tertiary-amine-thiourea compound and the terminal electrophile, N-fluorobenzenesulfonimide, to give fluorinated products in 72-95% yield with up to 99:1 d.r. and 98% ee. Notably, these products contain adjacent tertiary and α-fluoro quaternary stereocenters (see scheme).

Highly Enantioselective Inverse‐Electron‐Demand Hetero‐Diels–Alder Reactions Catalyzed by Modularly Designed Organocatalysts

With the exponential developments of organocatalytic methods in recent years, organocatalysis has now been established as a very powerful tool for the synthesis of functional molecules. Most recently, there was considerable interest in applying self-assembled organocatalysts in catalytic reactions. Compared to conventional organocatalysts, the structure of self-assembled organocatalysts is easy to modify and optimize due to the fact that synthesis is not involved in the final catalyst formation step. Moreover, it is very convenient to build a large catalyst library of these self-assembled organocatalysts for high-throughput screenings. Several self-assembled organocatalysts have been reported since the seminal work of Clarke and co-workers; nonetheless, the reactions catalyzed by these catalysts are still very limited. Most of the reported catalytic systems can only catalyze Michael and/or aldol reactions through the enamine mechanism. In 2008, we developed the modularly designed organocatalysts (MDOs) through the self-assembly of amino acids and cinchona alkaloids through ionic interactions ACHTUNGTRENNUNG(Scheme 1). Previously we demonstrated that these

Highly enantioselective three-component direct mannich reactions of unfunctionalized ketones catalyzed by bifunctional organocatalysts

A highly stereoselective three-component direct Mannich reaction between aromatic aldehydes, p-toluenesulfonamide, and unfunctionalized ketones was achieved through an enolate mechanism for the first time with a bifunctional quinidine thiourea catalyst. The corresponding N-tosylated β-aminoketones were obtained in high yields and excellent diastereo- and enantioselectivities (up to >99:1 dr and >99% ee).

Acetylphosphonate as a Surrogate of Acetate or Acetamide in Organocatalyzed Enantioselective Aldol Reactions

Highly enantioselective aldol reactions of acetylphosphonates and activated carbonyl compounds was realized with cinchona alkaloid derived catalysts, in which the acetylphosphonate was directly used as an enolate precursor for the first time. The aldol product obtained was converted in situ to its corresponding ester or amide through methanolysis or aminolysis. The overall process may be viewed as formal highly enantioselective acetate or acetamide aldol reactions, which are very difficult to achieve directly with organocatalytic methods.

Highly Diastereodivergent Synthesis of Tetrasubstituted Cyclohexanes Catalyzed by Modularly Designed Organocatalysts

A highly diastereodivergent synthesis of tetrasubstituted cyclohexanes has been achieved using modularly designed organocatalysts (MDOs) which are self-assembled in situ from amino acids and cinchona alkaloid derivatives. Diastereodivergence is realized through controlling the stereoselectivity of the individual steps of a tandem Michael/Michael reaction. Up to 8 of the 16 possible stereoisomers have been successfully obtained in high stereoselectivities using MDOs for the tandem reaction and an ensuing epimerization. The method was used in the enantioselective synthesis of the natural products (-)-α- and β-lycoranes.

Enantioselective ring-opening of meso-epoxides by aromatic amines catalyzed by a homochiral metal–organic framework

The enantioselective ring-opening of meso-epoxides by aromatic amines was achieved by using a new chiral metal-organic framework . The corresponding α-hydroxyamines were obtained with good yields and ee values (up to 89% ee).

Diastereodivergent Catalysis Using Modularly Designed Organocatalysts: Synthesis of both cis‐ and trans‐Fused Pyrano[2,3‐b]pyrans

Both enantiomers of cis- and trans-fused 3,4,4a,8a-tetrahydro-2H,5H-pyrano[2,3-b]pyran-7-carboxylates have been obtained in high diastereoselectivities and enantioselectivities from the same starting materials using a tandem inverse-electron-demand hetero-Diels-Alder/oxa-Michael reaction catalyzed by modularly designed organocatalysts (MDOs). Diastereodivergence was achieved in these reactions through the direct control of the stereochemistry of the bridgehead atoms of the fused ring using new MDOs self-assembled from both enantiomers of proline and cinchona alkaloid thiourea derivatives.

List-Barbas-Mannich reaction catalyzed by modularly designed organocatalysts.

The List-Barbas-Mannich reaction of ethyl (p-methoxyphenylimino)acetate (p-methoxyphenyl = PMP) with unmodified aldehydes or ketones catalyzed by modularly designed organocatalysts (MDOs) that are self-assembled from proline and cinchona alkaloid thioureas (such as a quinidine-derived thiourea) produces the corresponding γ-oxo-α-amino acid derivatives in high yields and excellent stereoselectivities. No solvent is necessary for this reaction. Aldehydes are especially good substrates for this reaction: The reaction takes only a few minutes to yield the corresponding List-Barbas-Mannich products in excellent dr (up to >99:1) and ee values (up to >99% ee).

One‐Pot Sequential Organocatalysis: Highly Stereoselective Synthesis of Trisubstituted Cyclohexanols

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96%) synthesis of trisubstituted cyclohexanols was achieved by using a one-pot sequential organocatalysis that involved a quinidine thiourea-catalyzed tandem Henry-Michael reaction between nitromethane and 7-oxo-hept-5-en-1-als followed by a tetramethyl guanidine (TMG)-catalyzed tandem retro-Henry-Henry reaction on the reaction products of the tandem Henry-Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one-pot sequential organocatalysis by using the racemic Henry product as the substrate.