手性胍催化酮与1,4-二噻烷-2,5-二醇的串联反应

合成了三种轴手性多氢键胍催化剂,并将其用于催化α,β-不饱和酮和1,4-二噻烷-2,5-二醇的不对称Sulfa-Michael/Aldol串联反应。研究表明:在室温(25℃)时,2mL THF作为溶剂,轴手性胍(1c)作为催化剂,催化剂1c用量为10mol%,能较好地串联该反应,并以较好的收率(75～88%)和较高的对映选择性(80～89%ee)以及较好的非对映选择性(94∶6 dr)获得了目标产物。     

奎宁衍生的新型手性胍催化剂的合成及其在不对称Michael加成反应中的应用研究

以生物碱奎宁和不同胺为原料,通过4步反应合成了5种新型手性胍催化剂,其结构经¹H NMR, ¹³C NMR, IR和HR-MS(ESI)表征。探索了一系列奎宁衍生的手性胍催化剂催化硝基乙烯类化合物和硫代丙二酸酯的不对称Michael加成反应。通过优化反应条件,确定最佳条件为：5 mol% 5e为催化剂,乙醚为溶剂,于20 ℃反应5 h。在此条件下进行了底物拓展,获得一系列2-(1-芳基-2硝基乙基)丙二酸二苯二硫酯,最高收率为92%,最高对映选择性为93%。     

有机小分子催化不对称Henry反应的研究进展

综述了各类有机小分子催化剂(如金鸡纳碱衍生物、手性(硫)脲、手性二级胺、金鸡纳碱-硫脲衍生物、胍-硫脲衍生物等)在不对称Henry反应中的研究进展。参考文献18篇。     

手性叔胺脲催化靛红亚胺与苯胺的不对称aza-Mannich反应

报道了Takemoto型手性(硫)脲催化靛红亚胺与苯胺的不对称aza-Mannich反应。在0.1 mmol反应量下,筛选出最佳催化剂体系为：10 mol%催化剂N-[3,5-二(三氟甲基)苯基]-N′-[(1S,2S)-2-(二甲氨基)环己基]脲1d,1 mL乙醚,0℃反应。以71～82%的收率和最高达97%ee获得系列手性3-N,N′-靛红缩酮。     

有机小分子催化的不对称Strecker反应研究进展

有机小分子催化的不对称合成反应是目前研究最为活跃的领域之一. 不对称Strecker反应是合成光学活性α-氨基酸衍生物的有效手段. 目前报道的催化不对称Strecker反应的有机催化剂主要有手性胍类、手性(硫)脲衍生物、氮-氧偶极化合物、手性Brønsted酸等, 取得了良好的催化活性和对映选择性. 对各类有机小分子催化剂在有机催化不对称Strecker反应中的应用研究进展, 以及催化剂结构与反应条件对催化活性和不对称诱导作用的影响进行了简要评述.     

MCM-41固载的(1R,2R)-1,2-环己二胺与Ru(II))复合催化剂的合成、表征及不对称氢转移反应的催化应用

不对称催化是用催化量的手性物质催化,获得大量对映体纯物质的经济、可行的方法之一.其中不对称氢转移反应就是用手性氨基醇或手性二胺作为手性催化剂配体、Ru( )作为催化中心,以异丙醇或甲酸为氢源,可将潜手性的酮或亚氨还原成相应的对映体纯的醇或胺[1～5](Scheme1),反应的转化率和ee值都很高[6],并且具有反应条件温和(室温)、操作简单、反应原料价廉易得,它的逆反应可用来动态拆分外消旋的二级醇[7],因此应用前景广阔.但该反应所用催化剂价格昂贵,并且回收困难.为此,我们尝试了将手性的(1R,2R)-1,2-环己二胺以共价键键合的方法,固…     

叔胺硫脲催化的2,5-二羟基-1,4-二噻烷与氮叔丁氧羰基醛亚胺的不对称[3+2]环化反应

以双功能手性叔胺硫脲作为催化剂,用于催化2,5-二羟基-1,4-二噻烷与氮叔丁氧羰基(N-Boc)醛亚胺的不对称[3+2]环化反应.实验结果表明,在10%(摩尔分数)手性催化剂的作用下,反应底物均能高产率地转化成目标产物,并且得到高达95%的对映选择性和7∶1的非对映选择性,实现了一系列含有四氢噻唑骨架的双手性中心化合物的合成.     

有机催化靛红亚胺与1,3二羰基化合物的不对称Mannich反应

将Takemoto型(硫)脲及方酰胺衍生物催化剂用于靛红亚胺与1,3-二羰基化合物的不对称Mannich反应,筛选出最佳催化剂体系为:10 mol%催化剂1h,1 mLCHCl₃为溶剂,室温反应,以82～92%的产率和最高达94%的对映选择性获得手性3-氨基-2-吲哚酮化合物。     

手性吡咯亚磷酰胺/Rh催化的1,1-双取代烯烃的不对称氢甲酰化反应

发展了一类吡咯取代的手性亚磷酰胺配体,并将其成功地应用于铑催化的1,1-双取代烯烃的不对称氢甲酰化反应,以优秀的区域选择性、良好的化学选择性和对映选择性(71%～86%ee)得到相应的手性直链醛,反应的转化数(TurnoverNumber,TON)值最高达到8900.该类催化剂容易制备且具有广泛的官能团兼容性,通过不对称氢甲酰化反应为手性α-烷基-β-甲酰基丙酸酯类化合物的合成提供了一类新的方法.     

双噁唑啉接枝的氨基酸聚合物作为手性催化中心在不对称Henry反应中的应用

通过控制聚合单体L-谷氨酸-γ-乙酯和DL-半胱氨酸以及聚合过程中引发剂与单体的比例,制备了一系列溶解性能不同的氨基酸聚合物.利用其作为负载手性配体的载体,通过双噁唑啉配体上的双键和聚合物上巯基的加成反应,合成了一系列双噁唑啉接枝氨基酸聚合物.将合成的聚合物作为可回收的手性催化剂用于催化不对称Henry反应,反应选择性(e. e.值)在50%～90%之间,产率在67%～95%之间.该催化剂可以循环使用至少7次而不需要经过重新活化.     

A convenient synthesis and the mesomorphic properties of new chiral ferroelectric thiobenzoates

A secondary chiral (R)-(?)-2-alcohol underwent the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and ethyl 4-hydroxybiphenylcarboxylate, resulting in the desired (S)-(+)-product with high enantiomeric purity (>99% ee), with the chiral branched chain attached to the biphenyl. This method is operationally simple and provides the very important chiral precursor in good yields (62% in dry THF and 72% in dry Et₂O). The condensation of the (S)-(+)-acid chloride from this material and a suitable 4-n-alkylthiophenol in toluene in the presence of pyridine or triethylamine furnishes the chiral (S)-(+)-thiobenzoate liquid crystals in good yields (80–83% in pyridine and 65–68% in Et₃N). (S)-(+)-4-(1-Methylheptyloxy)biphenyl 4-alkylthiobenzoates are abbreviated (S)-MHOBSn , where n varies from 4 to 10 and denotes the number of carbon atoms in the alkyl chain. DSC, polarizing microscopy and X-ray diffraction showed that the (S)-MHOBSn series possesses a rich phase polymorphism: two highly ordered tilted phases CrG* and SmI*, as well as the ferroelectric smectic C (SmC*) and chiral nematic (N*) phase. In this series, the seldom observed transition between the chiral phases SmI*–SmC* is seen. All the compounds possess stable enantiotropic SmC* and N* phases. The existence of weak intermolecular hydrogen-bonding in (S)-MHOBSn was confirmed by FTIR spectroscopy.     

Synthesis of Poly(Ethylene Glycol)–Supported (R)-BINOL Derivatives and Their First Application in Enantioselective Mukaiyama Aldol Reactions

The Mukaiyama aldol reaction of 2-styryl-oxazole-4-carbaldehyde (1) as model substrate with S-ketene silyl acetal 2 catalyzed by poly(ethylene glycol)-supported binaphthyl-derived chiral titanium(IV) complexes afforded the corresponding aldol product in good to excellent yields and enantioselectivities up to 94% ee. The chemical yields and/or the enantioselectivities are enhanced by generating the active catalyst from Ti(OiPr)₄, polymer-supported ligands (R)-6 or (R)-8, and chiral or achiral promoters. Pyrrolidine derivative (S)-13 and trifluoromethyl-substituted phenol 12 are the most efficient additives found.     

Stereoselective Dithiophosphorylation of Cinchona Alkaloids: Easy Approach to Prospective Chiral Ligands and Organocatalysts

Abstract

The 9-mesylates of Cinchona alkaloids reacted with HSP(S)(OEt)₂ in benzene at 50°C to give the corresponding O,O-diethyl-dithiophosphates of the alkaloids with complete inversion of configuration at the 9-C stereogenic centers (3 examples, 42–45% yields). Also O-ethyl-dithiophosphoric acid derivative of 9-epi-quinine was obtained. The configuration of the stereogenic centers were established using homo- and hetero-NOE NMR techniques and comparing the experimental and calculated (GIAO/DFT) spectra. The dithiophosphates of alkaloids were tested as chiral ligands in the Pd-catalyzed allylic alkylation of dimethyl malonate with rac-1,3-diphenylprop-2-enyl acetate and in the Cu-catalyzed asymmetric Henry reaction and gave the respective product with up to 51% ee. Quinine O,O-diethyl-phosphorodithioate was also tested as a novel potential chiral solvating agent for amino acids (N-Boc-phenylglycine) in ³¹P and ¹H NMR spectroscopy.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental files: Additional figures]     

Synthesis of (+)- and (−)-Tetrabenazine from the Resolution of α-Dihydrotetrabenazine

Abstract

Tetrabenazine (1) was reduced with NaBH₄ to α-dihydrotetrabenazine (2) and then resolved with di-p-toluoyl-L-tartrate and di-p-toluoyl-D-tartrate to subsequently give (+)- and (?)-α-dihydrotetrabenazine. The enantiomers were oxidized under Swern conditions to prepare samples of (+)-tetrabenazine and (?)-tetrabenazine. The samples were optically pure by chiral HPLC analysis.     

Catalytic Hydrogenation of Chiral 2-(2-Furyl)-3,4-dimethyl-5-phenyloxazolidine

Reduction of chiral 2-(2-furyl)-3,4-dimethyl-5-phenyloxazo-lidines-1,3 by H₂/Raney nickel proceeds simultaneously as hydrogenation of the furan ring and opening of the oxazolidine ring on C2-O bond. Diastere-oselectivity in the first reaction was established as ca 40% and 80% depending on the configuration of the oxazolidine 1 and 2.     

Synthesis of Novel Chiral C 2-symmetric Diaza-18-crown-6 Ether Derivatives and their Enantioselective Recognition of Amino Acid Derivatives

New chiral diaza-18-crown-6 ether derivatives, 5 and 6 were synthesized from (R)-(-)-2-amino-1-bütanol. These chiral artificial receptors exhibit pronounced chiral recognition toward the enantiomers of l- and d- amino acid derivatives. The highest enantioselectivity was observed in the case of Trp-OMe·HCl (K_D/K_L=12.5).     

Hydrogen bond-induced ferroelectric liquid crystals

Abstract

Hydrogen-bonded dimers of 4-alkoxy-4′-stilbazole homologues (C _n OSB, proton acceptors) and the mono-(2-methylbutyl)ester of terephthalic acid (MBTA, proton donor) behaved like conventional thermotropic mesogens. For chiral MBTA mixtures, chiral nematic and blue phases were observed with n = 1 and 2, and chiral smectic C phases were observed with n ≥ 5. Achiral phases were observed for mixtures with racemic MBTA as proton donor. Transition temperatures and enthalpies are similar for the chiral and achiral systems.     

Ferroelectric liquid crystal materials synthesized from 2(S)-[2(S)-methylbutyloxy]propanol

Abstract

A new chiral alcohol, 2(S)-[2(S)-methylbutyloxy]propanol (3), containing two chiral centres has been synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. It was used as a chiral building block for the preparation of ferroelectric liquid crystal materials. Several of the new materials exhibit an enantiotropic S*_c phase with a wide temperature range. The results indicate that the molecular structure of 3 is useful for synthesizing ferroelectric liquid crystal materials.     

Synthesis of Chiral Aromatic Alcohols: Use of New C2-Symmetric RhIIICp∗, RuII(cymene), or RuII(benzene) Complexes Containing Chiral Diaminocyclohexane Ligand as Asymmetric Transfer Hydrogenation Catalyst

Abstract

Twelve chiral secondary alcohols were synthesized by asymmetric transfer hydrogenation (ATH) using C₂-symmetric bis(sulfonamide) ligand (2) derived from (1R,2R)-cyclohexane-1,2-diamine and complexed with [RhCl₂Cp?]₂, [RuCl₂(cymene)]₂, or [RuCl₂(benzene)]₂ and then used in situ in the reduction of prochiral ketones. The alcohols were obtained in 85–99% yield and 90–99% enantioselectivity with isopropanol as the hydrogen source. Two-fold rate enhancement and better yields were achieved (88–99%) with 80–99% enantioselectivity using the complex [RhCl₂Cp?]₂ and aqueous sodium formate as the hydrogen source.     

Asymmetric oxidation of sulfides catalyzed by (R)-6,6'-dibromo-BINOL derived titanium complex

Abstract

An efficient asymmetric oxidation of sulfides was achieved using (R)-6,6'-dibromo-BINOL as chiral ligand in combination with Ti(OⁱPr)₄ using 70% aqueous tertiary butyl hydroperoxide as oxidant. The resulting sulfoxides had high enantiopurities and good yields. A range of aryl alkyl and aryl benzyl sulfides were oxidized to the corresponding sulfoxides with 78–95% ee in 72–80% yields.