溶剂和杂多酸盐中季铵阳离子对环己烯环氧化反应控制相转移催化的影响

 考察了溶剂和催化剂Q3［PO4（WO3）4］中季铵盐阳离子对环己\r\n烯环氧化反应的影响．在环己烯环氧化反应中，以氯仿和叔丁醇为溶剂\r\n时，环氧化反应的结果最好．当催化剂中季铵盐阳离子的碳数合适时，\r\n才能形成反应控制相转移催化过程．催化剂本身不溶于反应体系，但在\r\n过氧化氢的作用下形成可溶于反应体系的活性物种，均相地催化环氧化\r\n反应．当过氧化氢消耗尽时，催化剂又恢复到起始结构并从反应体系中\r\n析出．     

Towards Asymmetric Catalysis in the Major Groove of 1,1′‐Binaphthalenes

Four new diphosphane ligands, (R)‐ 4 , (R)‐ 5 , (S)‐ 6 , and (R)‐ 7 (Schemes 3, 4, 6, and 7), featuring metalcoordination sites located in the major groove of chiral 1,1′‐binaphthalene clefts, were prepared in enantiomerically pure form. The performance of this new class of ligands was tested in enantioselective, Pd‐catalyzed allylic alkylation reactions with acyclic and cyclic methyl carbonates 28 – 30 as substrates under various reaction conditions (Schemes 8 and 9). Using sodium phenyl sulfinate as a nucleophile, the reactivity of the catalysts formed with the new ligands and suitable palladium precursors was found satisfactory (>90%); however, the ee values were in all cases poor (<4%). Slightly better results were obtained using anions of dimethyl malonate as nucleophiles, but, also in these cases, the ee values never exceeded 17% (Table). ³¹P‐NMR‐Spectroscopic investigations revealed the formation of multiple‐catalyst species in solution (Fig. 2), and molecular modeling suggested a lack of embedding of the coordinated substrate in a `chiral pocket' (Fig. 3), which probably accounts for the observed low level of enantioselectvity.     

Asymmetric Catalysis with a Phosphoramidite Derived from (−)‐(aR)‐ [1,1′‐Binaphthalene]‐8,8′‐diol

Treatment of (aR)‐[1,1′binaphthalene]‐8,8′‐diol ((−)‐ 1 ) with hexamethylphosphorous triamide afforded the N,N‐dimethylphosphoramidite (−)‐ 3 (Scheme 1). The synthesis of the analogous N,N‐diisopropylphosphoramidite 4 failed, however, and afforded the acyclic phosphonamidate (−)‐ 5 . The application of the cyclic phosphoramidite (−)‐ 3 towards asymmetric catalysis was investigated. The borane reduction of acetophenone ( 6 ) to (R)‐1‐phenylethanol ( 7 ) in the presence of (−)‐ 3 proceeded with 96% ee (Scheme 2). The use of (−)‐ 3 as ligand in several Cu‐catalyzed addition and substitution reactions resulted in enantioselectivities ranging from 0 to 50% (Schemes 3 and 4).     

Stereoselective Synthesis of 1,1′‐Disaccharides by Organoboron Catalysis

The highly stereoselective synthesis of 1,1′‐disaccharides was achieved by using 1,2‐dihydroxyglycosyl acceptors and glycosyl donors in the presence of a tricyclic borinic acid catalyst. In this reaction, the complexation of the diols and the catalyst is crucial for the activation of glycosyl donors, as well as for the 1,2‐cis‐configuration of the products. The anomeric stereochemistry of the glycosyl donor depends on the employed glycosyl donor. Applications of the produced 1,1′‐disaccharides are also described.     

Negative Cooperativity in the Molecular Recognition of Excitatory Amino-Acid Derivatives by Synthetic Allosteric 1,1′-Binaphthalene Receptors

The optically active allosteric receptors (−)-(R,R)- 3 and (+)-(R,R)- 4 were synthesized for the molecular recognition of the N-(benzyloxy)carbonyl (N-Cbz)-protected excitatory amino acids aspartic acid (Asp, 1 ) and glutamic acid (Glu, 2 ). These macrocyclic structures consist of two 1,1′-binaphthalene moieties connected by two but-2-yne-1,4-diyl (for (−)-(R,R)- 3 ) or p-xylylene (for (+)-(R,R)- 4 ) bridges between the O-atoms in the minor grooves. Each 1,1′-binaphthalene moiety contains two 2-acetamidopyridin-6-yl (CONH(py)) H-bonding sites in the major groove to bind excitatory amino-acid derivatives via two COOH█bk█⋅⋅⋅█ek█CONH(py) H-bonding arrays and additional secondary electrostatic interactions. The formation of stable complexes with 1 : 2 host-guest stoichiometry was proven by the evaluation of fluorescence binding titrations using a multiple-wavelength nonlinear least-squares curve-fitting procedure, Job plot analysis, and solubilization experiments. Complexation of the first excitatory amino-acid guest at binding site 1 reduces the affinity for the second guest at binding site 2. As measures for the negative cooperativity between the two sites, the ratios of the association constants for the first and second binding events, {K_a(1 : 1)/K_a(1 : 2)}_corr. (corrected for the statistical preference of the 1 : 1 complex formation), were found to adopt values between 1.4 and 2.4, and the Hill coefficients n_H varied between 0.49 and 0.59.     

Atropselective Dibrominations of a 1,1′‐Disubstituted 2,2′‐Biindolyl with Diverging Point‐to‐Axial Asymmetric Inductions. Deriving 2,2′‐Biindolyl‐3,3′‐diphosphane Ligands for Asymmetric Catalysis

On the ¹H NMR timescale, 2,2′‐biindolyls with (R)‐configured (1‐alkoxyprop)‐2‐yl, (1‐hydroxyprop)‐2‐yl, or (1‐siloxyprop)‐2‐yl substituents at C‐1 and C‐1′ are atropisomerically stable at <0 °C and interconvert at >30 °C. A 2,2′‐biindolyl (R,R)‐ 17 a of that kind and achiral (!) brominating reagents gave the atropisomerically stable 3,3′‐dibromobiindolyls (M)‐ and/or (P)‐ 18 a at best atropselectively—because of point‐to‐axial asymmetric inductions—and atropdivergently, exhibiting up to 95 % (M)‐ and as much (P)‐atropselectivity. This route to atropisomerically pure biaryls is novel and should extend to other substrates and/or different functionalizations. The dibromobiindolyls (M)‐ and (P)‐ 18 a furnished the biindolyldiphosphanes (M)‐ and (P)‐ 14 without atropisomerization. These syntheses did not require the resolution of a racemic mixture, which distinguishes them from virtually all biaryldiphosphane syntheses known to date. (M)‐ and (P)‐ 14 acted as ligands in catalytic asymmetric allylations and hydrogenations. Remarkably, the β‐ketoester rac‐ 25 c was hydrogenated trans‐selectively with 98 % ee; this included a dynamic kinetic resolution.     

Synthesis and properties of polyimides from 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride

4,4′-Binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride was synthesized from 4-chloro-1,8-naphthalic anhydride and polymerized with aromatic and pliphatic diamines in m-cresol or N-methyl-2-pyrrolidinone (NMP). The polyimides, except for two derived from p-phenylenediamine and hydrazine, are soluble in 1,1,2,2-tetrachloroethane and NMP. Their intrinsic viscosities ranged from 0.36 to 2.20 dL/g. The polymers showed excellent thermal and thermooxidative stabilities and displayed weak glass transition temperatures. Young's moduli of some polymer films were in the range of 2.5 and 5.4 GPa at 30°C. The aliphatic polyimides exhibited a stronger fluorescence than the aromatic polyimides. © 1995 John Wiley & Sons, Inc.     

H-Bond Mediated Phase-Transfer Catalysis: Enantioselective Generating of Quaternary Stereogenic Centers in β-Keto Esters

In this work, we would like to present the development of a highly optimized method for generating the quaternary stereogenic centers in β-keto esters. This enantioselective phase-transfer alkylation catalyzed by hybrid Cinchona catalysts allows for the efficient generation of the optically active products with excellent enantioselectivity, using only 1 mol% of the catalyst. The vast majority of phase-transfer catalysts in asymmetric synthesis work by creating ionic pairs with the nucleophile-attacking anionic substrate. Therefore, it is a sensible approach to search for new methodologies capable of introducing functional groups into the precursor’s structure, maintaining high yields and enantiomeric purity.     

Synthesis and Characterization of Fluorinated Polyimide Derived from 3,3′‐Diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane

A novel aromatic diamine monomer, 3,3′‐diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane (PAFM), was successfully synthesized by coupling of 2‐isopropylaniline and 3,4‐difluorobenzaldehyde. The aromatic diamine was adopted to synthesize a series of fluorinated polyimides by polycondensation with various dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) via the conventional one‐step method. These polyimides presented excellent solubility in common organic solvents, such as N,N‐dimethylformamide (DMF), N,N‐dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N‐methyl‐2‐pyrrolidone (NMP), chloroform (CHCl₃), tetrahydrofuran (THF) and so on. The glass transition temperatures (T_g) of fluorinated polyimides were in the range of 260–306°C and the temperature at 10% weight loss in the range of 474–502°C. Their films showed the cut‐off wavelengths of 330–361 nm and higher than 80% transparency in a wavelength range of 385–463 nm. Moreover, polymer films exhibited low dielectric properties in the range of 2.76–2.96 at 1 MHz, as well as prominent mechanical properties with tensile strengths of 66.7–97.4 MPa, a tensile modulus of 1.7–2.1 GPa and elongation at break of 7.2%–12.9%. The polymer films also showed outstanding hydrophobicity with the contact angle in the range of 91.2°–97.9°.     

Synthesis and property of soluble poly(1,1′-dialkyl-3,3′-ferrocenylenevinylene)s via titanium-induced dicarbonyl-coupling reaction of 1,1′-dialkylferrocene-3,3′-dicarbaldehydes

1,1′-Dialkylferrocene-3,3′-dicarbaldehydes ( 1a–c ) with long alkyl chains such as ethyl, hexyl, and dodecyl groups were prepared in 13–25% yield via three-step reactions. The titanium-induced dicarbonyl-coupling reaction of 1a–c gave poly(1,1′-dialkyl-3,3′-ferrocenylenevi-nylene)s ( 2a–c ) in quantitative yields, which were the molecular weights of 3000–10,000 and highly soluble in chloroform, benzene, and hexane. The electrical conductivity and the third-order nonlinear optical susceptibility for poly(1,1′-dihexyl-3,3′-ferrocenylenevinylene) ( 2b ) were estimated to be 1 × 10^?2 S/cm on doping with iodine and 1–4 × 10^?12 esu at a wavelength of 1–2.4 μm, respectively. © 1995 John Wiley & Sons, Inc.