Synthesis of 2-amino-1,3-dienes by chromium-catalyzed addition of silylated propargyl bromides to imines

(Silyl)methylallenic amines were synthesized by the chromium-catalyzed addition of (4-bromobutynyl)trimethylsilane to tosyl imines. Regioisomeric mixtures of the desired allene and the corresponding alkyne were obtained. Allenic imines were then treated with TBAF to afford 2-aminomethyl-1,3-dienes in good yields (62-92%). In the presence of a Lewis acid, silylallenic imines were added to benzaldehyde dimethylacetal to give highly functionalized dienes with excellent yields and good to excellent diastereomeric ratios.     

A synthesis of unsymmetrical chiral salen ligands derived from 2-hydroxynaphthaldehyde and substituted salicylaldehydes

Novel unsymmetrical chiral salen Schiff base ligands have been synthesised via a stepwise approach. A special feature of these ligands is that they possess two different units: a 2-hydroxynaphthaldehyde moiety on one side and a substituted salicylaldehyde on the other.     

Enantioselective alkynylation of aromatic aldehydes catalyzed by new chiral oxazolidine ligands

New chiral oxazolidines were conveniently synthesized from natural amino acids in three simple steps with good yields. The use of chiral oxazolidine ligands for the enantioselective alkynylation of aldehydes provides a simple, practical and inexpensive method to generate chiral propargyl alcohols with 85-99% ee.     

New chiral diamide ligands containing redox-active hydroquinone groups. Synthesis and results in the palladium(II)-catalyzed 1,4-diacetoxylation of 1,3-dienes

Chiral ligands 8-11, 22 and 23 were synthesized from different chiral diamines as a new class of ligands for the Pd(II)-catalyzed 1,4-diacetoxylation of 1,3-dienes. The synthesis from the diamines and protected benzoic acids was performed in a few simple steps and gave the ligands in high overall yields. The hydroquinone groups present in the ligands are in situ oxidized to benzoquinone to give the active ligands. Application of these ligands in the 1,4-diacetoxylation reaction afforded the oxidation product with high regio- and diastereoselectivity and an enantiomeric excess up to 42% was obtained. Possible coordination modes of the metal to the ligand are discussed, and experiments were made to investigate the coordination by varying the reaction conditions or making changes to the ligands.     

Enantioselective addition of phenyl and alkyl acetylenes to imines catalyzed by chiral Cu(I) complexes

The stereoselective addition of phenyl acetylene and alkyl acetylenes to imines, catalyzed by chiral bis-imines-Cu(I) complexes was studied. A very simple experimental procedure allowed to obtain at room temperature optically active propargyl amines in very good yields and enantioselectivity up to 81%.     

Application of chiral tetrahydropentalene ligands in rhodium-catalyzed 1,4-addition of (E)-2-phenylethenyl- and (Z)-propenylboronic acids to enones

Chiral tetrahydropentalenes (3aR,6aR)-1 have been prepared and used as ligands in the Rh-catalyzed 1,4-addition of 1-alkenylboronic acids to cyclic enones 5. It has been discovered that the stereochemistry of the reaction was controlled by the steric properties of the aryl groups in 1 rather than their electronic nature. In the vinylation with (E)-2-phenylethenylboronic acid 5, ligands (3aR,6aR)-1 provided enantioselectivity up to 87% ee and gave high yields of ethenylketones 6 in the presence of 1 (6.6 mol %). The configuration of all ketone products obtained with (3aR,6aR)-1 is (S). Rh-catalyzed reaction of cyclopentenone 4a and (Z)-propenylboronic acid 7 in the presence of ligands (3aR,6aR)-1 yielded at 50 °C an inseparable mixture of (Z)- and (E)-ketones 8 with (Z)-8 as the major product and both in only moderate enantiomeric excess.     

Chiral imidates as a new class of nitrogen-based chiral ligands: synthesis and catalytic activity in asymmetric aziridinations and diethylzinc additions

Chiral imidates were efficiently synthesized in one step and with high yields (seven examples). These chiral imidates were used as ligands in the Cu(I)-catalyzed asymmetric aziridination of methyl cinnamate and in the asymmetric diethylzinc additions to benzaldehyde as a proof of principle. The imidate catalyst system showed high catalytic activities and induced encouraging selectivities. An X-ray structure analysis of an imidate-Cu(I) complex is included, showing a distorted tetrahedral arrangement with two bidentate ligand molecules surrounding the metal.     

N-烷基化手性氨基醇配体的合成

本实验制备了不同构型的两种N-单烷基和N-双烷基的新的手性氨醇配体。     

Novel chiral C2-symmetric multidentate aminophosphine ligands for use in catalytic asymmetric reduction of ketones

A series of novel chiral C₂-symmetric multidentate aminophosphine ligands have been successfully synthesized by Schiff-base condensation of bis（o-formylphenyl）phenylphosphane and easily available monoprotected（1R,2R）-diaminocyclohexane.The catalytic properties of these ligands were investigated in Ir-catalyzed asymmetric transfer hydrogenation of various aromatic ketones,giving the corresponding optical active alcohols with up to 98%conversion and good ee under mild reaction conditions.     

Synthesis of chiral 2-alkyl-8-quinolinyl-oxazoline ligands: reversal of enantioselectivity in the asymmetric palladium-catalyzed allylic alkylation

New chiral 2-alkyl-8-quinolinyl-oxazolines were synthesized from 2-alkyl-8-quinolinecarboxylic acids and enantiomerically pure amino alcohols using a convenient procedure. Enantioselective palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate in the presence of 2-alkyl-8-quinolinyl-oxazolines provided an alkylation product with an opposite configuration compared to those obtained from unsubstituted quinolinyl-oxazoline ligands.     

Enantioselective synthesis of homoallylic alcohols via a chiral In(III)-PYBOX complex

In the presence of 20 mol% of a chiral catalytic complex prepared from In(OTf)(3) and chiral PYBOX, allyltributylstannane reacted with aldehydes to afford the corresponding homoallylic alcohols in moderate to high enantioselectivities (60-93% ee).     

Enantioselective synthesis of nitrocyclopropanes via conjugate addition of bromomalonate to nitroalkenes catalyzed by Ni(II) complexes

A novel one-pot methodology for the catalytic enantioselective synthesis of highly functionalized nitrocyclopropanes promoted by chiral nickel complexes is developed. The treatment of bromomalonates with nitroalkenes under the mild reaction conditions afforded the corresponding Michael adducts which cyclizes to controlled reaction conditions with excellent diasteroselectivities (>99 de) and enantioselectivities (up to 99% ee).     

Enantioselective addition of diethylzinc to aldehydes catalyzed by 5-cis-substituted proline derivatives

5-Cis-substituted prolinols, prolinamines, and prolinamine sulfonamides proved to be efficient ligands for the enantioselective addition of diethylzinc to aldehydes, providing up to 99% ee. The sense of asymmetric induction can be controlled by the nature of the exocyclic functional group (CPh₂OH vs. CH₂NHR vs. CH₂NHSO₃R). The additional 5-cis substituent exerts a strong beneficial effect on the chirality transfer since it rigidifies the catalyst structure. The stereochemical outcome of the reactions is discussed in detail on the respective transition states.     

Enantioselective phenyl transfer to aldehydes using 1,1′-bi-2-naphthol-3,3′-dicarboxamide as chiral auxiliary

N,N,N′,N′-Tetra-n-butyl-BINOL-3,3′-dicarboxamide 5d was found to promote phenyl transfer from ethylphenylzinc to both aromatic and aliphatic aldehydes with high enantioselectivity up to 96% ee in tert-butyl methyl ether.     

Synthesis of tertiary 1,3-butadien-2-ylcarbinols from chromium-catalyzed addition of (4-bromobut-2-ynyl)trimethylsilane to ketones

The synthesis of 1,3-butadien-2-ylcarbinols containing a tertiary alcohol is achieved by desilylation of (trimethylsilyl)methylallenic alcohols. The latter are obtained via a chromium-catalyzed addition of (4-bromobut-2-ynyl)trimethylsilane to aliphatic or aromatic ketones. The desired adducts are obtained in yields ranging from 21% to 67% for this two-step, one-pot process.     

Diastereoselective synthesis of enantioenriched homopropargyl amino alcohols from α-dibenzylamino aldehydes and their use as chiral synthons

Homochiral α-dibenzylamino aldehydes, prepared from the corresponding α-amino acids, react with propargyl bromide and zinc in DMF/THF (1:1) or DMF/Et₂O (1:1) at 20 °C to afford, in good yields and dr, homopropargylic 1,2-amino alcohols. anti Diastereomers were always formed as major products in this reaction. These compounds are versatile intermediates for a variety of synthetic targets: γ-amino-β-hydroxy-ketones, 4-amino-1,3-diols, 1,7-diamino-2,6-diols, and ω-amino-δ-hydroxy esters.     

New chiral bis(diphenylphospholane) ligands: design, synthesis, and application to catalytic enantioselective aldol reaction to ketones

New chiral bidentate diphenylphospholanes were designed targeting a catalytic enantioselective aldol reaction to ketones. Ligands 5l and 5m having cis-2-butenyl and cyclopropyl groups at the linker part, respectively, were identified as effective chiral ligands for a CuF-catalyzed enantioselective aldol reaction to ketones. Catalysts prepared from CuF·3PPh₃·2EtOH and these ligands produced ketone aldol products with up to 66% ee, which is promising particularly for this extremely difficult and important catalytic enantioselective carbon-carbon bond forming reaction. The enantioselectivity was strongly dependent on the linker structure. Construction of a deep chiral pocket around the copper metal with stable bidentate chelation is the key to meaningful enantioinduction.     

Enantioselective allylation of alkyl glyoxylates catalyzed by (salen)chromium(III) complexes

The enantioselective addition of allylstannanes and allylsilanes to alkyl glyoxylates of type 1, catalyzed by chiral (salen)Cr(III) complexes 3, has been studied. We have found that the reaction proceeded smoothly for low loading (1-2 mol %) of (1R,2R)-(salen)Cr(III)BF₄3a or (1R,2R)-(salen)Cr(III)ClO₄3c, and allyltributyltin under simple, undemanding conditions, affording (R)-2-hydroxypent-4-enoic acid esters 2 in good yield (61-90%) and enantioselectivity (58-76% ee).     

Asymmetric hydrophosphonylation of aldehydes catalyzed by bifunctional chiral Al(III) complexes

A new bifunctional chiral Al(III) complex of BINOL derivative, which contained tert-amine at 3,3′-position of the BINOL, has been developed for the effective enantioselective hydrophosphonylation of aldehydes. A variety of aromatic, heteroaromatic, condensed-ring, α,β-unsaturated, and aliphatic aldehydes were found to be suitable substrates for the reaction, and the desired α-hydroxy phosphonate were obtained in good to excellent yields (up to 99%) with moderate to good enantioselectivities (up to 87% ee) under mild conditions (at 0 °C). A possible catalytic cycle based on the experimental results was proposed.