Kinetic model for the chiral symmetry breaking transition in the growth front of a conglomerate crystal phase

In its molten phase, 1,1'-binaphthyl is racemic due to its high racemization rate, but it can crystallize as a conglomerate of R and S crystals. Our experiments have indicated that, under some conditions, the crystal growth front of 1,1'-binaphthyl shows many of the characteristics of an open system in which chiral symmetry is broken; i.e., the growing solid phase becomes predominantly R or S. Here we present a kinetic model to explain the observed chiral symmetry breaking. The model is based on growth due to attachment of R or S growth units to a crystal surface in a supercooled melt. Chiral symmetry breaking occurs due to chirally autocatalytic formation of R or S growth units on the growth surface. Unlike the many models suggested and studied in the 1980s, there is no cross-inhibition between R- and S-enantiomer in the model presented here. In our model, asymmetric and symmetric steady-state solutions that do not intersect were found. Through linear stability analysis, the critical point, at which a symmetric solution becomes unstable and makes a transition to an asymmetric solution, is determined.     

一种新的具有双螺旋结构特征的光学活性分子方的设计、合成及其光学性质

分别从手性构型高度稳定的(R)和(S)-2,2'-二乙炔基-1,1'-联萘模板出发, 通过保护基的控制导入、偶联反应、保护基脱去以及分子间偶合成环4个步骤成功地合成了一种具有螺旋结构特征的新的光学活性分子方(Molecular square)(R,R,R,R)-1和(S,S,S,S)-1. 用MS, IR, UV-Vis, 1H和13C NMR以及元素分析等方法对目标化合物进行了结构表征. 测定并分析比较了2个目标化合物的比旋光度[α]D和圆二色性(CD)等光学性质. 在CH2Cl2溶液中, 异构体(R,R,R,R)-1和(S,S,S,S)-1的[α]25D值分别为+887.3°和-889.7°, 并且其CD谱表现出对称的镜像特征.     

手性联萘基-2,2'-联吡啶及其衍生物的合成及其在不对称合成中的应用

利用Kröhnke方法,以芳基乙酮为原料一锅法简洁地合成了6-芳基-6'-溴-2,2'-联吡啶2b~2d。 通过(R)-3-(4,4,5,5-四甲基-1,3,2-二噁唑硼烷基)-2,2'-乙氧基-1,1'-联萘((R)-1)与6-溴-2,2'-联吡啶及其衍生物2a~2d的Suzuki偶联, 合成了4种手性6-[3-((R)-2,2'-二乙氧基-1,1'-联萘)基]-2,2'-联吡啶(R)-3a~3d。 将配体(R)-3a~3d应用于苯乙酮的不对称氢转移反应中,配体(R)-3a给出92%的转化率和4%的对映体过量(ee)值。     

Chiral bisphosphine BINAP-stabilized gold and palladium nanoparticles with small size and their palladium nanoparticle-catalyzed asymmetric reaction

The reduction of tetrachloroaurate or potassium tetrachloropalladate with sodium borohydride in the presence of optically active 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl [BINAP] gave the chiral (S)- or (R)-BINAP-stabilized gold or palladium nanoparticles which showed the small core (1.7 nm for BINAP-Au and 2.0 nm for BINAP-Pd) with narrow size distribution and remarkably high stability. Asymmetric hydrosilylation of styrene with trichlorosilane in the presence of chiral BINAP-Pd nanoparticles afforded an optically active 1-phenyl-1-trichlorosilylethane which was converted into an optically active 1-phenylethanol (95% enantiomeric excess) by oxidative cleavage of the carbon-silicon bond.     

Three-dimensional description of the spontaneous onset of homochirality on the surface of a conglomerate crystal phase

The spontaneous emergence of homochirality in an initially racemic system can be obtained in far-from-equilibrium states. Traditional models do not take into account the influence of inhomogeneities, while they may be of great importance. What would happen when one configuration emerges at one position, and the opposite one at another position? We present a discrete three-dimensional model of conglomerate crystallization, based on 1,1'-binaphthyl crystallization experiments, that takes into account the position and environment of every single elementary growth subunit. Stochastic simulations were performed to predict the evolution of the crystallization process. It is shown that the traditional view of the symmetry breaking can then be extended. Fluctuations of the fixed points related to inhomogeneities are observed, and complex behavior, such as local instabilities, transient structures, and chaotic behavior, can emerge. Our modeling indicates that such complex phenomena could cause large fluctuation of the final enantiomeric excess that is observed experimentally in binaphthyl crystallization. The results presented in this article show the importance of inhomogeneities in understanding enantiomeric excess generated in crystallization and the inadequacy of the models based on the assumption of homogeneity.     

Enantioresolution of 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl oxide using inclusion complex with chiral 2,2'-dihydroxy-1,1'-binaphtyl

An enantioresolution of 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl oxide (BINAPO) into its enantiomers was achieved using the inclusion complex with a commerciallyavailable chiral 2,2'-dihydroxy-1,1'-binaphthyl ((R)-BINOL), giving the two enantiomers with 99% ee and 72% ee, respectively.     

P-chirogenic binaphthyl-substituted monophosphines: synthesis and use in enolate vinylation/arylation reactions

[reaction: see text] New phosphine ligands possessing both axial chirality and a chirogenic phosphorus center were prepared from (R)-2-bromo-2'-N,N-(dimethylamino)-1,1'-binaphthyl (1) via a simple Li-halogen exchange protocol. The asymmetric vinylation of a ketone enolate with (R,R(P))-2-(tert-butylphenylphosphino)-2'-N,N-(dimethylamino)-1,1'-binaphthyl (2a) afforded the coupling product with good enantiomeric excess.     

First optically active molecular electronic wires

[structure: see text]. The optically active molecular electronic wires (S)- and (R)-7 containing an oligo-arylene-ethynylene structure and a chiral 1,1'-binaphthyl unit are synthesized. These molecules are incorporated into nanowell devices by self-assembly on the gold surface. In the nanowell devices, the median currents from the molecules containing both S and R enantiomers are significantly smaller than those from the pure S or R molecule. Compounds (R)- and (S)-7 are also less conductive than the fully conjugated oligo-phenylene-ethynylene-thiol molecules.     

Palladium-catalyzed asymmetric silaboration of allenes

An enantioselective silaboration of allenes was achieved using an achiral silylborane in the presence of a palladium catalyst bearing a chiral monodentate phosphine ligand. (R)-2-Bis(3,5-dimethylphenyl)phosphino-1,1'-binaphthyl gave the highest enantioselectivities in the addition of (diphenylmethylsilyl)pinacolborane to the internal C=C bond of terminal allenes at 0 degrees C, giving the corresponding beta-borylallylsilanes in high yields with high enantiomeric excesses. The enantioselectivity depended on the bulkiness of substituents of allenes: the enantiomeric excesses were found to be 91-93% ee (R = tert- and sec-alkyl), 88-90% ee (R = aryl), and 80-82% ee (R = prim-alkyl and Me) at 0 degrees C. Perfect chirality transfer was observed in the intramolecular cyclization reactions of the functionalized allylsilanes, affording highly enantioenriched cyclic alkenylboranes, which underwent Suzuki-Miyaura coupling with aryl halides.     

Enantiomerically pure 2-bromo-2'-diphenylphosphinyl-1,1'- binaphthyl as a monophosphorus template for electrophilic functionalization in chiral MOP-type ligand synthesis

[reaction: see text] Pd-catalyzed monophosphinylation of (R)-2-bromo-2'-iodo-1,1'-binaphthyl with Ph(2)P(O)H afforded (R)-2-bromo-2'-diphenylphosphinyl-1,1'-binaphthyl in good yield with excellent chemoselectivity and no observable racemization. Subsequent lithiation in the presence of excess thiosulfonate furnished an enantiomerically pure sulfenylation product, which was reduced to afford a chiral S-MOP ligand.     

手性联萘胺衍生物为配体的铜络合物催化下某些烯烃的不对称环丙烷化反应

以1,1'-联萘-2,2'-二胺为手性源合成了8对16种光活性铜络合物,考察了它们对1,1-二苯乙烯、苯乙烯和2,5-二甲基-2,4-己二烯等3种烯烃的不对称环丙烷化反应的光学诱导活性.结果表明,以旋光活性联萘胺同水杨醛及2-羟基萘甲醛缩合而得到的Schiff碱为配体的铜络合物的催化效果最佳.催化剂对2,5-二甲基-2,4-己二烯的催化效果优于其它两种烯烃.     

Mechanism of preferential enrichment,an unusual enantiomeric resolution phenomenon caused by polymorphic transition during crystallization of mixed crystals composed of two enantiomers

The mechanism of Preferential Enrichment, an unusual enantiomeric resolution phenomenon observed upon recrystallization of a series of racemic crystals which are classified as a racemic mixed crystal with fairly ordered arrangement of the two enantiomers, has been studied. On the basis of the existence of polymorphs and the occurrence of the resulting polymorphic transition during crystallization from solution, the mechanism has been accounted for in terms of (1) a preferential homochiral molecular association to form one-dimensional chain structures in the supersaturated solution of the racemate or nonracemic sample with a low ee value, (2) a kinetic formation of a metastable crystalline phase retaining the homochiral chain structures in a process of nucleation, (3) a polymorphic transition from the metastable phase to a stable one followed by enantioselective liberation of the excess R (or S) enantiomers from the transformed crystal into solution at the beginning of crystal growth to result in a slight enrichment (up to 10% ee) of the opposite S (or R) enantiomer in the deposited crystals, together with an enantiomeric enrichment of the R (or S) enantiomer in the mother liquor, and (4) a chiral discrimination by the once formed S (or R)-rich stable crystalline phase in a process of the subsequent crystal growth, leading to a considerable enantiomeric enrichment of the R (or S) enantiomer up to 100% ee in the mother liquor. The processes (3) and (4) are considered to be directly responsible for an enrichment of one enantiomer in the mother liquor. The association mode of the two enantiomers in solution has been investigated by means of (i) the solubility measurement and (ii) the number-averaged molecular weight measurement in solution by vapor pressure osmometry, together with (iii) the molecular dynamics simulation of oligomer models. The polymorphic transition during crystallization has been observed visually and by means of the in situ FTIR technique and DSC measurement. Both metastable and stable crystals have been obtained, and their crystal structures have been elucidated by X-ray crystallographic analysis of their single crystals.     

Embedding an allylmetal dimer in a chiral cavity: the unprecedented stereoselectivity of a twofold wittig [1,2]-rearrangement

After alpha,alpha'-dimetalation, both 2,2'-diallyloxy-1,1'-binaphthyl and 2,2'-di-2-methylallyloxy-1,1'-binaphthyl undergo the Wittig rearrangement with perfect diastereoselectivity. When racemic 1,1'-binaphthyl-2,2'-diol ("BINOL") is used as the starting material, it gives rise to a 1:1 mixture of antipodal stereoisomers, whereas enantiomerically pure (M)-2,2'-diallyloxy-1,1'-binaphthyl affords (M)-(S,S)-1,1-(1,1'-binaphthyl-2,2'-diyl)bis(2-propen-1-ol) as the sole product. The (M)-(S,S)/(P)-(R,R) mixture resulting from the rearrangement of racemic 2,2'-diallyloxy-1,1'-binaphthyl can be effectively subjected to a kinetic racemate resolution by applying the Sharpless-Katsuki asymmetric epoxidation. The single-sided Wittig rearrangement of 2-allyloxy-2'-propyloxy-1,1'-binaphthyl proceeds without any diastereoselectivity as this substrate can only be monometalated and hence is incapable of intramolecular aggregate formation which is instrumental for the observed stereoselectivity.     

2,8'-disubstituted-1,1'-binaphthyls: a new pattern in chiral ligands

The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2'-(diphenylphosphino)-1,1'-binaphthyl (MOP, 19) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15-->18), followed by functional group transformations, involving C-P and C-N bond formation (18-->19 and 18-->23). Racemic intermediate 22 was resolved by co-crystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(-)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92% ee (after hydrolysis of the primary product).     

Synthesis and catalytic activity of group 5 metal amides with chiral biaryldiamine-based ligands

A new series of group 5 metal amides have been prepared from the reaction between V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) and chiral ligands, (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (1H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (2H(2)), (R)-6,6'-dimethyl-2,2'-bis(mesitoylamino)-1,1'-biphenyl (3H(2)), (R)-2,2'-bis(mesitylenesulfonylamino)-6,6'-dimethyl-1,1'-biphenyl (4H(2)), (R)-2,2'-bis(diphenylthiophosphoramino)-1,1'-binaphthyl (5H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (6H(2)), (R)-2,2'-bis[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (7H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-1,1'-binaphthyl (8H(2)), (S)-2-(mesitoylamino)-2'-(dimethylamino)-1,1'-binaphthyl (9H), and (R)-2-(mesitoylamino)-2'-(dimethylamino)-6,6'-dimethyl-1,1'-biphenyl (10H), which are derived from (R) or (S)-2,2'-diamino-1,1'-binaphthyl, and (R)-2,2'-diamino-6,6'-dimethyl-1,1'-biphenyl, respectively. Treatment of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 1 equiv of C(2)-symmetric amidate ligands 1H(2), 2H(2), 3H(2), 4H(2), and 5H(2), or Schiff base ligands 6H(2), 7H(2) and 8H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the vanadium amides (1)V(NMe(2))(2) (11), (2)V(NMe(2))(2) (14), (3)V(NMe(2))(2) (17), (5)V(NMe(2))(2) (22), (6)V(NMe(2))(2) (23) and (7)V(NMe(2))(2) (24), and niobium amides (1)Nb(NMe(2))(3) (12), (2)Nb(NMe(2))(3) (15), (3)Nb(NMe(2))(3) (18), (4)Nb(NMe(2))(3) (20) and [2-(3-Me(3)C-2-O-C(6)H(3)CHN)-2'-(N)-C(20)H(12)][2-(Me(2)N)(2)CH-6-CMe(3)-C(6)H(3)O]NbNMe(2)·C(7)H(8) (25·C(7)H(8)), and tantalum amides (1)Ta(NMe(2))(3) (13), (2)Ta(NMe(2))(3) (16), (3)Ta(NMe(2))(3) (19) and (4)Ta(NMe(2))(3) (21) respectively, in good yields. Reaction of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 2 equiv of C(1)-symmetric amidate ligands 9H or 10H at room temperature gives, after recrystallization from a toluene or n-hexane solution, the chiral bis-ligated vanadium amides (9)(2)V(NMe(2))(2)·3C(7)H(8) (27·3C(7)H(8)) and (10)V(NMe(2))(2) (28), and chiral bis-ligated metallaaziridine complexes (10)(2)M(NMe(2))(η(2)-CH(2)NMe) (M = Nb (29), Ta (30)) respectively, in good yields. The niobium and tantalum amidate complexes are stable in a toluene solution at or below 160 °C, while the vanadium amidate complexes degrade via diemthylamino group elimination at this temperature. For example, heating the complex (2)V(NMe(2))(2) (14) in toluene at 160 °C for four days leads to the isolation of the complex [(2)V](2)(μ-NMe(2))(2) (26) in 58% yield. These new complexes have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 12, 13, and 15-30 have further been confirmed by X-ray diffraction analyses. The vanadium amides are active chiral catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to good yields with good ee values (up to 80%), and the tantalum amides are outstanding chiral catalysts for the hydroaminoalkylation, giving chiral secondary amines in good yields with excellent ee values (up to 93%).     

Chiral symmetry breaking via crystallization of the glycine and α-amino acid system: a mathematical model

We introduce and numerically solve a mathematical model of the experimentally established mechanisms responsible for the symmetry breaking transition observed in the chiral crystallization experiments reported by I. Weissbuch, L. Addadi, L. Leiserowitz and M. Lahav, J. Am. Chem. Soc., 1988, 110, 561-567. The mathematical model is based on five basic processes: (1) the formation of achiral glycine clusters in solution, (2) the nucleation of oriented glycine crystals at the air/water interface in the presence of hydrophobic amino acids, (3) a kinetic orienting effect which inhibits crystal growth, (4) the enantioselective occlusion of the amino acids from solution, and (5) the growth of oriented host glycine crystals at the interface. We translate these processes into differential rate equations. We first study the model with the orienting process (2) without (3) and then combine both allowing us to make detailed comparisons of both orienting effects which actually act in unison in the experiment. Numerical results indicate that the model can yield a high percentage orientation of the mixed crystals at the interface and the consequent resolution of the initially racemic mixture of amino acids in solution. The model thus leads to separation of enantiomeric territories, the generation and amplification of optical activity by enantioselective occlusion of chiral additives through chiral surfaces of glycine crystals.     

Chiral Symmetry Breaking of Spiropyrans and Spirooxazines by Dynamic Enantioselective Crystallization

Dynamic enantioselective crystallization enabled the chiral symmetry breaking of two spiropyrans and one spirooxazine. The three spiro compounds afforded racemic conglomerate crystals, and easily racemized in alcoholic solution without irradiation. Optically pure enantiomorphic crystals were obtained by vapor-diffusion crystallization or attrition-enhanced deracemization (Viedma ripening). Their absolute configurations were determined by single-crystal X-ray analysis and each enantiomorphic crystal was correlated with its solid-state circular dichroism (CD) spectrum.     

高效液相色谱法测定1,1’-联萘-2,2’-二酚的光学纯度

用高效液相色谱法测定了1,1’-联禁-2,2’-二酚的光学纯度。色谱柱:Si-5柱,流动相:石油醚／乙醇（93／7,V／V）。方法简便、快速、准确,准确度为98.6％～101.6％,相对平均偏差为1.01％。     

Orthogonal packing of enantiomerically pure helical silver coordination networks

The combination of the chiral tecton based on the (R)-6,6'-dibromo-1,1'-binaphthyl moiety bearing two isonicotinoyl groups with AgX (X = BF4-, CF3SO3-, PF6-) leads to the formation of enantiomerically pure helical strands with orthogonal packing in the rare space group I2(1)3.     

Pseudoenantiomeric fluorescent sensors in a chiral assay

Two enantioselective fluorescent sensors, namely, the 1,1'-binaphthol (BINOL)-amino alcohol (S)-1 and the H(8)BINOL-amino alcohol (R)-2, have been prepared as a pseudoenantiomeric pair. These two compounds have the opposite chiral configuration at both the axially chiral biaryl centers and the amino alcohol units. In methylene chloride solution, (R)-mandelic acid greatly enhances the emission of (S)-1 at λ(1) = 374 nm and (S)-mandelic acid greatly enhances the emission of (R)-2 at λ(2) = 330 nm. A 1:1 mixture of (S)-1 and (R)-2 was used to interact with mandelic acid at a variety of concentrations with various enantiomeric compositions. It was found that both the concentration of mandelic acid and its enantiomeric composition can be directly determined by measuring the sum and difference of the fluorescence intensities at λ(1) and λ(2).