Asymmetric intramolecular Cannizzaro reaction of anhydrous phenylglyoxal

The use of anhydrous phenylglyoxal provides a solution to the problem of low reactivity in the asymmetric intramolecular Cannizzaro reaction with alcohols. Double asymmetric induction was achieved in the reaction of anhydrous phenylglyoxal with d-(+)-menthol promoted by a (S,S)-t-BuBox·copper(II) hexafluoroantimonate complex.     

新型手性硫醚-亚磷酰胺配体的设计与应用

根据模块组合法原理,设计并合成了一种具有亚磷酰胺结构的硫醚配体,该配体具有原料便宜易得、合成步骤简单、易于修饰和结构稳定等特点。以配体/钯络合物催化的丙二酸二甲酯与1,3-二苯基烯丙基醋酸酯的烯丙基化反应作为模板反应,探究了溶剂、碱对其立体控制的影响。随后探究了中心手性与轴手性的匹配/错配现象以及硫醚片段的空间位阻、电性对反应立体控制的作用。在最佳条件下,产物的对映选择性能够达到-76% ee。     

含氰基基团的以C为中心的不对称阴离子离子液体的合成、表征及应用

首次通过不对称阴离子的钠盐/钾盐和不同的季胺化的咪唑,吡咯溴盐/氯盐进行离子交换,合成了一系列含氰基官能团的不对称阴离子功能化离子液体。通过红外、核磁共振、质谱和元素分析对离子液体的结构进行表征;通过TGA对离子液体的热稳定性进行测定,结果发现不对称功能化离子液体具有良好的热稳定性,其分解温度在219-319℃范围内。将功能化离子液体[Bmim][C(CN)2COCH3]作为弱配体应用于模型的Suzuki偶联反应,发现在反应中加入功能化离子液体[Bmim][C(CN)2COCH3]可以使反应收率提高10-15%。     

5-L-孟氧基4-苄氨基丁烯内酯的不对称合成和晶体结构研究

温和条件下,苄胺与手性合成子5-(L)-孟氧基3-溴-2(5)呋喃酮通过串联的不对称迈克尔加成/分子内消除反应合成了一种新手性化合物:5-L-孟氧基-4-苄胺基丁烯内酯。产物经过IR、1H-NMR、MS谱学表征,并经X-ray单晶衍射测定了其结构。新化合物属于正交晶系,P212121空间群,a=5.2945(4),b=14.2829(10),c=26.0769(18),Mr=343.45,Z=4,V=1972.0(2)3,Dc=1.157g/cm3,μ(MoKα)=0.076mm-1,F(000)=744,R=0.0387,wR=0.0880。     

Synthesis of platinum complexes containing (+)-bornyl- and (−)-menthylammonium in the outer coordination sphere and their catalytic activity in hydrosilylation reactions

Optically active (+)-bornyl- and (−)-menthylammonium platinates were synthesized starting from H₂[PtCl₆] · 4H₂O and hydrochlorides of the corresponding amines. Catalytic activity of the complexes in the hydrosilylation reactions of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 1,1,3,3-tetramethyldisiloxane and acetophenone with diphenylsilane was studied. The addition of the siloxanes leads to a predominant formation of β-adduct. Activity of the catalysts, evaluated on the 50% conversion of the substrate, decreases in the following sequence: (−)-(menthylNH₃)₂[PtCl₆] > (Et₃NH)₂[PtCl₆] > (+)-(bornylNH₃)₂[PtCl₄] > (+)-(bornylNH₃)₂[PtCl₆]. Asymmetric induction is observed in the hydrosilylation of aceto-phenone in the presence of (+)-(bornylNH₃)₂[PtCl _n ] (n = 4, 6); (+)-(bornylNH₃)₂[PtCl₆] showed the highest catalytic activity and selectivity. The hydrosilylation of acetophenone gave 1-phenylethoxy(diphenyl)silane, 1-phenylvinyloxy(diphenyl)silane, and 2-phenylethyl-2-diphenylsiloxy(diphenyl)silane as the products. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–349, February, 2008.     

Density functional theory calculations of novel Rh(I) diphosphinite catalysts

Novel Rh(I) diphosphinite catalysts [Rh((R,R)-3,4-(bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol)]+ ([Rh-CANDYPHOS]+) and [Rh((R,R)-3,4-(bis(O-diphenylphosphino)-1,2,5,6-tetra-O-ethyl-chiro-inositol)]+ ([Rh-EtCP]+) have been prepared utilizing naturally-occurring resources. Potential energy surfaces for the catalyzed asymmetric hydrogenation of the prochiral enamides methyl-(Z)-α-acetamido cinnamate, methyl-(Z)-α-acetamido cinnamic acid and dimethyl itaconate have been surveyed using density function theory (DFT) methods. Key transition states were identified from previous [Rh((R,R)-DUPHOS)]+ studies for the two diastereoisomeric manifolds 1 and 2. Transition state energies were found starting from models based on (1) the X-ray structure of the active complex (CANDYPHOS)(η⁴-(Z,Z)-cyclo-octa-1,5-diene)-rhodium(I) tetrafluoroborate CHCl₃ solvate [3] and (2) models in which the complex (without substrate) started with C2 molecular symmetry. The difficulties encountered in calculations of the transition state energies of large cations are outlined and limitations noted. Transition state enthalpy values are compared with the observed experimental free energy differences results and previous studies 1 and 2. The predictive aspects of the calculations appear to be limited with the starting models playing an important part in the absolute value of the final energies.     

Enantioselective C--C bond formation to sulfonylimines through use of the 2-pyridinesulfonyl group as a novel stereocontroller

Enantioselective C--C bond formation to 2-pyridinesulfonylimines afforded products with good enantioselectivity. Dynamic induction of chirality on the sulfur by coordination of a chiral Lewis acid to the pyridine nitrogen and one of the prochiral sulfonyl oxygens induces enantioselectivity. Since the 2-pyridinesulfonyl group can easily be removed after the reaction, it acts not only as an activating group but also as an efficient stereocontroller.     

Role of the NH2 functionality and solvent in terdentate CNN alkoxide ruthenium complexes for the fast transfer hydrogenation of ketones in 2-propanol

The reaction of [RuCl(CNN)(dppb)] (1; HCNN=6-(4-methylphenyl)-2-pyridylmethylamine) with NaOiPr in 2-propanol/C6D6 affords the alcohol adduct alkoxide [Ru(OiPr)(CNN)(dppb)].n iPrOH (5), containing the Ru-NH2 linkage. The alkoxide [Ru(OiPr)(CNN)(dppb)] (4) is formed by treatment of the hydride [Ru(H)(CNN)(dppb)] (2) with acetone in C6D6. Complex 5 in 2-propanol/C6D6 equilibrates quickly with hydride 2 and acetone with an exchange rate of (5.4+/-0.2) s(-1) at 25 degrees C, higher than that found between 4 and 2 ((2.9+/-0.4) s(-1)). This fast process, involving a beta-hydrogen elimination versus ketone insertion into the Ru-H bond, occurs within a hydrogen-bonding network favored by the Ru-NH2 motif. The cationic alcohol complex [Ru(CNN)(dppb)(iPrOH)](BAr(f)4) (6; Ar(f)=3,5-C6H3(CF3)2), obtained from 1, Na[BAr(f)4], and 2-propanol, reacts with NaOiPr to afford 5. Complex 5 reacts with either 4,4'-difluorobenzophenone through hydride 2 or with 4,4'-difluorobenzhydrol through protonation, affording the alkoxide [Ru(OCH(4-C6H4F)2)(CNN)(dppb)] (7) in 90 and 85 % yield of the isolated product. The chiral CNN-ruthenium compound [RuCl(CNN)((S,S)-Skewphos)] (8), obtained by the reaction of [RuCl2(PPh3)3] with (S,S)-Skewphos and orthometalation of HCNN in the presence of NEt3, is a highly active catalyst for the enantioselective transfer hydrogenation of methylaryl ketones (turnover frequencies (TOFs) of up to 1.4 x 10(6) h(-1) at reflux were obtained) with up to 89% ee. Also the ketone CF3CO(4-C6H4F), containing the strong electron-withdrawing CF3 group, is reduced to the R alcohol with 64% ee and a TOF of 1.5 x 10(4) h(-1). The chiral alkoxide [Ru(OiPr)(CNN)((S,S)-Skewphos)]n iPrOH (9), obtained from 8 and NaOiPr in the presence of 2-propanol, reacts with CF3CO(4-C6H4F) to afford a mixture of the diastereomer alkoxides [Ru(OCH(CF3)(4-C6H4F))(CNN)((S,S)-Skewphos)] (10/11; 74% yield) with 67% de. This value is very close to the enantiomeric excess of the alcohol (R)-CF3CH(OH)(4-C6H4F) formed in catalysis, thus suggesting that diastereoisomeric alkoxides with the Ru-NH2 linkage are key species in the catalytic asymmetric transfer hydrogenation reaction.     

New benzo[h]quinoline-based ligands and their pincer Ru and Os complexes for efficient catalytic transfer hydrogenation of carbonyl compounds

New benzo[h]quinoline ligands (HCN'N) containing a CHRNH2 (R=H (a), Me (b), tBu (c)) function in the 2-position were prepared starting from benzo[h]quinoline N-oxide (in the case of ligand a) and 2-chlorobenzo[h]quinoline (for ligands b and c). These compounds were used to prepare ruthenium and osmium complexes, which are excellent catalysts for the transfer hydrogenation (TH) of ketones. The reaction of a with [RuCl2(PPh3)3] in 2-propanol at reflux afforded the terdentate CN'N complex [RuCl(CN'N)(PPh3)2] (1), whereas the complexes [RuCl(CN'N)(dppb)] (2-4; dppb=Ph2P(CH2)4PPh2) were obtained from [RuCl2(PPh3)(dppb)] with a-c, respectively. Employment of (R,S)-Josiphos, (S,R)-Josiphos*, (S,S)-Skewphos, and (S)-MeO-Biphep in combination with [RuCl2(PPh3)3] and ligand a gave the chiral derivatives [RuCl(CN'N)(PP)] (5-8). The osmium complex [OsCl(CN'N)(dppb)] (12) was prepared by treatment of [OsCl2(PPh3)3] with dppb and ligand a. Reaction of the chloride 2 and 12 with NaOiPr in 2-propanol/toluene afforded the hydride complexes [MH(CN'N)(dppb)] (M=Ru 10, Os 14), through elimination of acetone from [M(OiPr)(CN'N)(dppb)] (M=Ru 9, Os 13). The species 9 and 13 easily reacted with 4,4'-difluorobenzophenone, via 10 and 14, respectively, affording the corresponding isolable alkoxides [M(OR)(CN'N)(dppb)] (M=Ru 11, Os 15). The complexes [MX(CN'N)(P2)] (1-15) (M=Ru, Os; X=Cl, H, OR; P=PPh3 and P2=diphosphane) are efficient catalysts for the TH of carbonyl compounds with 2-propanol in the presence of NaOiPr (2 mol %). Turnover frequency (TOF) values up to 1.8x10(6) h(-1) have been achieved using 0.02-0.001 mol % of catalyst. Much the same activity has been observed for the Ru--Cl, --H, --OR, and the Os--Cl derivatives, whereas the Os--H and Os--OR derivatives display significantly lower activity on account of their high oxygen sensitivity. The chiral Ru complexes 5-8 catalyze the asymmetric TH of methyl-aryl ketones with TOF approximately 10(5) h(-1) at 60 degrees C, up to 97 % enatiomeric excess (ee) and remarkably high productivity (0.005 mol % catalyst loading). High catalytic activity (TOF up to 2.2x10(5) h(-1)) and enantioselectivity (up to 98 % ee) have also been achieved with the in-situ-generated catalysts prepared from [MCl2(PPh3)3], (S,R)-Josiphos or (S,R)-Josiphos*, and the benzo[h]quinoline ligands a-c.