Chiral Quaternary Ammonium Aryloxide/N,O‐Bis(trimethyl‐ silyl)acetamide Combination as Efficient Organocatalytic System for the Direct Vinylogous Aldol Reaction of (5H)‐Furan‐2‐one Derivatives

A chiral quaternary ammonium amide was generated in situ from N,O‐bis(trimethylsilyl)acetamide (BSA) as non‐nucleophilic Brønsted base precursor and the combination of chiral quaternary ammonium halide/sodium aryloxide as chiral Lewis base. This system was applied to an anti‐selective organocatalytic direct vinylogous aldol (ODVA) reaction of (5H)‐furan‐2‐one derivatives with aldehydes. Several 5‐(1′‐hydroxy)‐γ‐butenolides were obtained in good diastereomeric ratios (up to 95/5) and excellent enantioselectivities (up to 94%) with both aliphatic or (hetero)aromatic aldehydes, so providing a rare example of general and efficient conditions for the ODVA reaction.     

Superparamagnetic Nanoparticle‐Supported (S)‐Diphenyl‐ prolinol Trimethylsilyl Ether as a Recyclable Catalyst for Asymmetric Michael Addition in Water

A new superparamagnetic nanoparticle‐supported (S)‐diphenylprolinol trimethylsilyl ether (Jørgensen–Hayashi catalyst) was synthesized and applied for the asymmetric Michael addition of aldehydes to nitroalkenes in water, which gives products in moderate to good yields (up to 96%), good enantioselectivity (up to 90% ee) and diastereoselectivities (up to 99:1). The immobilized catalyst could be easily separated from the reaction by an external magnet and recycled for four times without significant loss of catalytic efficiency.     

Highly Efficient Asymmetric Three‐Component Vinylogous Mannich Reaction Catalyzed by a Chiral Scandium(III)‐ N,N′‐Dioxide Complex

The asymmetric three‐component vinylogous Mannich reaction of an acyclic silyl dienol ester, an aldehyde and 2‐aminophenol was accomplished using a chiral N,N′‐dioxide‐scandium(III) complex as the catalyst. A variety of aldehydes were found to be suitable substrates for the reaction and the desired δ‐amino‐α,β‐unsaturated esters were obtained in 90–99% yields with good to excellent enantioselectivities (up to >99% ee) and complete regioselectivities. Moreover, the simple experimental procedures were air‐tolerant and convenient. The present catalytic process provides the potential for large‐scale syntheses of the chiral δ‐amino‐α,β‐unsaturated esters.     

Asymmetric Aza‐Morita–Baylis–Hillman‐Type Reactions: The Highly Enantioselective Reaction between Unmodified α,β‐ Unsaturated Aldehydes and N‐Acylimines by Organo‐co‐catalysis

The highly enantioselective organo‐co‐catalytic aza‐Morita–Baylis–Hillman (MBH)‐type reaction between N‐carbamate‐protected imines and α,β‐unsaturated aldehydes has been developed. The organic co‐catalytic system of proline and 1,4‐diazabicyclo[2.2.2]octane (DABCO) enables the asymmetric synthesis of the corresponding N‐Boc‐ and N‐Cbz‐protected β‐amino‐α‐alkylidene‐aldehydes in good to high yields and up to 99% ee. In the case of aza‐MBH‐type addition of enals to phenylprop‐2‐ene‐1‐imines, the co‐catalytic reaction exhibits excellent 1,2‐selectivity. The organo‐co‐catalytic aza‐MBH‐type reaction can also be performed by the direct highly enantioselective addition of α,β‐unsaturated aldehydes to bench‐stable N‐carbamate‐protected α‐amidosulfones to give the corresponding β‐amino‐α‐alkylidene‐aldehydes with up to 99% ee. The organo‐co‐catalytic aza‐MBH‐type reaction is also an expeditious entry to nearly enantiomerically pure β‐amino‐α‐alkylidene‐amino acids and β‐amino‐α‐alkylidene‐lactams (99% ee). The mechanism and stereochemistry of the chiral amine and DABCO co‐catalyzed aza‐MBH‐type reaction are also discussed.     

Enantioselective Aza‐Henry Reaction of Imines Bearing a Benzothiazole Moiety Catalyzed by a Cinchona‐Based Squaramide

An efficient enantioselective aza‐Henry reaction of nitroalkanes to imines bearing a benzothiazole moiety catalyzed by a Cinchona‐based squaramide has been developed. In the reaction of imines, the corresponding products were obtained in good to excellent yields (up to 99%) with excellent enantioselectivities (up to >99% ee) for most of the aromatic substituted imines. The imines with electron‐withdrawing groups gave better yields than those bearing electron‐donating groups in the aza‐Henry reaction. Moreover, a one‐pot three‐component enantioselective aza‐Henry reaction using 2‐aminobenzothiazoles, aldehydes, and nitromethane was also developed. Moderate to good yields and high enantioselectivities were obtained in the one‐pot cases (up to 98% ee).     

Organocatalyzed Highly Enantioselective and anti‐Selective Construction of γ‐Butenolides through Vinylogous Mukaiyama Aldol Reaction

The formation of chiral γ‐butenolides has been achieved with good yields (up to 90%), high enantioselectivity (up to 91%) and diastereoselectivity (up to 9/1, anti‐selective) through an organocatalyzed vinylogous Mukaiyama aldol reaction of 2‐(trimethylsilyloxy)furan and aldehydes. A wide range of chiral γ‐butenolides was obtained under mild conditions by this methodology.     

One‐Pot Synthesis of cis‐Isoquinolonic Acid Derivatives via Three‐Component Reaction of Homophthalic Anhydride with Aldehydes and Amines using Ytterbium(III) Triflate as Catalyst

Ytterbium(III) triflate efficiently catalyzes the one‐pot reaction of homophthalic anhydride with aldehydes and amines at ambient temperature to afford the corresponding cis‐isoquinolonic acid derivatives in good to excellent yields with high diastereoselectivity. This method provides a novel and much improved modification of the three‐component reaction in terms of mild reaction conditions, short reaction times, clean reaction profiles, small quantity of catalyst, and simple work‐up procedure. Another important feature of this method is that the catalyst can be easily recovered from the aqueous layer after the reaction and can be reused with no loss of activity.     

Iron(III) Chloride‐Catalyzed Tandem Aza‐Prins/Friedel–Crafts Cyclization of 2‐Arylethyl‐2,3‐butadienyl Tosylamides and Aldehydes‐An Efficient Synthesis of Benzo[f]isoquinolines

An efficient approach for the synthesis of 1,2,3,4,5,6‐hexahydrobenzo[f]isoquinolines via a tandem aza‐Prins/Friedel–Crafts cyclization from 2‐arylethyl‐2,3‐butadienyl tosylamides and aldehydes has been developed. This iron(III) chloride‐catalyzed cascade cyclization at the room temperature with different types of aldehydes, such as aromatic and heteroaromatic aldehydes, alkyl aldehydes, and α,β‐unsaturated aldehydes, affords the products in moderate to excellent yields (up to 97 %). In this reaction, chlorotrimethylsilane was applied to activate the aldehydes. The cheap catalyst, the mild reaction conditions, and the broad scope of the substrates make this method highly useful.

     

Activated α,β‐Unsaturated Aldehydes as Substrate of Dihydroxyacetone Phosphate (DHAP)‐Dependent Aldolases in the Context of a Multienzyme System

The utility for carbon‐carbon bond formation of a multienzyme system composed of recombinant dihydroxyacetone kinase (DHAK) from Citrobacter freundii, the fructose bisphosphate aldolase from rabbit muscle (RAMA) and acetate kinase (AK) for adenosine triphosphate (ATP) regeneration has been studied. Several aldehydes with great structural diversity, including three α,β‐unsaturated aldehydes, have been analysed as acceptor substrates. It was found that α,β‐unsaturated aldehydes bearing an electron‐withdrawing group in the β position to the double bond with a trans configuration are good acceptors for RAMA in this multienzyme system. The aldol reaction proceeds with excellent D ‐threo enantioselectivity and the aldol adduct is obtained in good overall yield. The L ‐threo and D ‐erythro enantiomers are also accessible from rhamnulose 1‐phosphate aldolase (Rha‐1PA) and fuculose 1‐phosphate aldolase (Fuc‐1PA) catalysed reactions, respectively.     

Novel environmentally benign procedure for the synthesis of 2‐aryl‐ and 2‐hetaryl‐4(3H)‐quinazolinones

A novel environmentally benign procedure for the synthesis of 2‐aryl‐ or 2‐hetaryl‐4(3H)‐quinazolinones by condensation of anthranilamide with various aromatic aldehydes in polyethylene glycol under microwave irradiation has been developed. In contrast with other reported methods, this procedure provides the corresponding quinazolinones with good to high yields and purity, in very short reaction times and without the use of an oxidant.     

Enantioselective Vanadium‐Catalyzed Oxidation of 1,3‐Dithianes from Aldehydes and Ketones using β‐Amino Alcohol Derived Schiff Base Ligands

The asymmetric vanadium‐catalyzed oxidation of 1,3‐dithianes from aldehydes and ketones by β‐amino alcohol‐derived Schiff base ligands with two stereogenic centers was investigated. Using aqueous hydrogen peroxide as the oxidant and the Schiff base 3b as a chiral ligand, a variety of 1,3‐dithianes derived from aldehydes were easily converted into the corresponding mono‐sulfoxides in good yields (81–88%) with excellent enantioselectivities (up to 99% ee). Additionally, 99% ee was obtained for the enantioselective vanadium‐catalyzed oxidation of the 1,3‐dithianes derived from ketones. We found a slight kinetic resolution when using a higher ratio of hydrogen peroxide during the oxidation of the aldehyde‐derived 1,3‐dithianes but not in the ketone‐derived 1,3‐dithianes.     

Synthesis of an Enantiocomplementary Catalyst of β‐Isocupreidine (β‐ICD) from Quinine

Compound 20 , a pseudoenantiomer of β‐isocupreidine (β‐ICD), was synthesized from quinine employing a Barton reaction of nitrosyl ester 13 and acid‐catalyzed cyclization of carbinol 18 as key steps. The Baylis–Hillman reaction of benzaldehyde, p‐nitrobenzaldehyde, and hydrocinnamaldehyde with 1,1,1,3,3,3‐hexafluoroisopropyl acrylate (HFIPA) using 20 as a chiral amine catalyst was found to give the corresponding S‐enriched adducts in high optical purity (>91% ee) in contrast to the β‐ICD‐catalyzed reaction which affords R‐enriched adducts. This result suggests that compound 20 can serve as an enantiocomplementary catalyst of β‐ICD in the asymmetric Baylis–Hillman reaction of aldehydes with HFIPA.     

Synthesis of 2‐Aminobenzothiazoles via Copper(I)‐Catalyzed Cross‐Coupling with Part‐Per‐Million Catalyst Loadings

An efficient protocol has been developed for the preparation of 2‐aminobenzothiazoles via a copper(I)‐catalyzed tandem reaction of 2‐iodoanilines with isothiocyanates at very low catalyst loadings [typically 50 ppm of copper(I) iodide (CuI)]. A variety of 2‐iodoanilines could be cross‐coupled with isothiocyanates, affording 2‐aminobenzothiazoles in moderate to good yields (49–93%) under the given conditions. The turnover number (TON) of this reaction reaches 67,000 and the reaction could be scaled up, at least, to the gram‐scale.     

Asymmetric Domino Nitro‐Michael/Horner–Wadsworth–Emmons Reaction for Disubstituted Cyclohexenecarboxylate Annulation: Efficient Synthesis of Dipeptidyl Peptidase IV Inhibitor ABT‐341 and Influenza Neuraminidase Inhibitor

An asymmetric domino nitro‐Michael/Horner–Wadsworth–Emmons (HWE) reaction involving α,β‐unsaturated aldehydes and nitro phosphonates has been developed, which gave 4,5‐disubstituted cyclohexenecarboxylates with high stereoselectivities (dr up to >20:1, ee 83–92%) in good yields (44–76%). Furthermore, using this methodology as a key step, a short and practical synthesis of pharmaceutically useful compounds (such as the dipeptidyl peptidase IV inhibitor ABT‐341 and an influenza neuraminidase inhibitor) has also been accomplished.     

Phase‐Transfer‐Catalyzed Enantioselective Mannich Reaction of Malonates with α‐Amido Sulfones

The highly enantioselective reaction between in situ generated, Cbz‐protected azomethines and malonates in the presence of 150 mol % of potassium carbonate (50 % w/w) and 1 mol % of quinine‐derived quaternary ammonium bromides as phase‐transfer organocatalysts has been developed. This study reports a novel approach for the asymmetric Mannich‐type reaction and a wide range of azomethines, including those derived from enolizable aldehydes, is tolerated by the present system. The adducts, obtained in excellent yields with ee up to 98 %, are suitable precursors of optically pure β‐amino acids.     

Enantioselective Additions of Aryltitanium Tris(isopropoxide) to Ketones: Structure of [(i‐PrO)2Ti{μ‐(S)‐BINOLate}(μ‐O‐i‐Pr)TiPh(O‐i‐Pr)2], Study of Mechanistic and Stereochemical Insights

Aryl addition reactions of ArTi(O‐i‐Pr)₃ to aromatic, heteroaromatic, or α,β‐unsaturated ketones are described, producing tertiary alcohols in good to excellent enantioselectivities of up to 97% ee. The structure of the dititanium complex [(i‐PrO)₂Ti{μ‐(S)‐BINOLate}(μ‐O‐i‐Pr)TiPh(O‐i‐Pr)₂] [(S)‐ 4 ] that simultaneously bears a chiral directing ligand and a nucleophile is reported. Complex (S)‐ 4 possesses a pocket structure and has been illustrated as the key active species for addition reactions of both aldehydes and ketones. Mechanistic and stereochemical insights concerning addition reactions of organometallic reagents to organic carbonyls are rationalized based on the pocket structure and pocket size of (S)‐ 4 .     

Bis(3,5‐dimethylphenyl)‐(S)‐pyrrolidin‐2‐ylmethanol: an Improved Organocatalyst for the Asymmetric Epoxidation of α,β‐Enones

The asymmetric epoxidation of α,β‐enones by the readily available bis(3,5‐dimethylphenyl)‐(S)‐pyrrolidin‐2‐ylmethanol and tert‐butyl hydroperoxide (TBHP) is described. Stereoelectronic substitution on the aryl moiety of diaryl‐2‐pyrrolidinemethanols was found to significantly affect the efficiency with respect to the previously reported (S)‐diphenyl‐2‐pyrrolidinemethanol. Improved reactivity and enantioselectivity were achieved with bis(3,5‐dimethylphenyl)‐(S)‐pyrrolidin‐2‐ylmethanol at reduced catalyst loading (20 mol %) with ees up to 94% for chalcone epoxides under mild reaction conditions, whereas (S)‐diphenyl‐2‐pyrrolidinemethanol afforded a maximum ee of 80%. Interestingly, the methodology is applicable to the epoxidation of more challenging aliphatic or enolizable enones with good control of the asymmetric induction (up to 87% ee).     

Amine‐Catalyzed Asymmetric Epoxidation of α,β‐Unsaturated Aldehydes

The direct organocatalytic enantioselective epoxidation of α,β‐unsaturated aldehydes with different peroxides is presented. Proline, chiral pyrrolidine derivatives, and amino acid‐derived imidazolidinones catalyze the asymmetric epoxidation of α,β‐unsaturated aldehydes. In particular, protected commercially available α,α‐diphenyl‐ and α,α‐di(β‐naphthyl)‐2‐prolinols catalyze the asymmetric epoxidation reactions of α,β‐unsaturated aldehydes with high diastereo‐ and enantioselectivities to furnish the corresponding 2‐epoxy aldehydes in high yield with up to 97:3 dr and 98 % ee. The use of non‐toxic catalysts, water and hydrogen peroxide, urea hydroperoxide or sodium percarbonate as the oxygen sources could make this reaction environmentally benign. In addition, one‐pot direct organocatalytic asymmetric tandem epoxidation‐Wittig reactions are described. The reactions were highly diastereo‐ and enantioselective and provide a rapid access to 2,4‐diepoxy aldehydes. Moreover, a highly stereoselective one‐pot organocatalytic asymmetric cascade epoxidation‐Mannich reaction, which proceeds via the combination of iminium and enamine activation, is presented. The mechanism and stereochemistry of the amino acid‐ and chiral pyrrolidine‐catalyzed direct asymmetric epoxidation of α,β‐unsaturated aldehydes are also discussed.     

4,4′‐Disubstituted L‐Prolines as Highly Enantioselective Catalysts for Direct Aldol Reactions

A new series of 4,4′‐disubstituted prolines ( 1a–h ) has been developed and tested as organocatalysts in the direct catalytic asymmetric aldol reaction of several aliphatic ketones with aldehydes. Catalyst 1g affords the best enantioselectivities for this transformation. The reaction was carried out in DMF using a catalyst loading of 10 mol % at −10 °C to give the aldol products in up to 97 % ee for acetone. In the cases of cyclohexanone and cyclopentanone, the corresponding anti‐products were obtained in 94 % ee.     

An Organocatalytic Domino Thia‐Michael/Aldol Condensation Reaction: Highly Enantioselective Synthesis of Functionalized Dihydrothiophenes

An organocatalytic domino thia‐Michael/aldol condensation reaction of α, β‐unsaturated aldehydes with 1, 4‐dithiane‐2,5‐diol catalyzed by chiral diphenylprolinol TMS ether has been developed, which provides a new practical and direct route to chiral dihydrothiophenes with high yields (up to 90%) and excellent enantioselectivities (up to>99% ee). The catalytic mechanism of the domino reaction was further confirmed through the APCI‐MS detection of proposed reaction intermediates.