Organometallische komplexverbindungen: VIII. Einfluss von achiralen substituenten auf die optische induktion bei der metallinduzierten synthese von 3-methyl-E-4-hexen-2-on

Bis(μ-methyl-1,3-dimethyl-η³-allylnickel) which has been modified by P ligands with a chiral substituent reacts with carbon monoxide under the formation of optically active 3-methyl-E-4-hexen-2-on. The investigated P ligands (PR^★R₂) have one chiral substituent (R^★ = 1R,3R,4S-(?)-menthyl) and the other substituents have been varied by taking the same alkyl or alkoxy groups (R = Me, Et, i-Pr, OMe, OEt, O-i-Pr). It has been found that the extent and the direction of optical induction depends on the concentration of the P-ligand and the kind of the achiral substituents at phosphorus.     

Methylidyne tricobalt nonacarbonyl clusters; optically active silicon and germanium derivatives,and substitutions at silicon

The preparation and alcoholysis of chiral chlorosilanes containing the nonacarbonyltricobaltcarbon cluster, RR′Si(Cl)CCo₃(CO)₉, is described. The alkoxy derivatives react with i-Bu₂AlH or BF₃ · Et₂O to give the corresponding silicon hydride or fluoride. Reaction of methylidynetricobalt nonacarbonyl with optically active silanes of germane gave the optically active cluster complexes R¹R²R³M^*CCo₃(CO)₉ (M^* = Si, Ge). These compounds react with phosphine to give the monosubstituted R¹R²R³M^*CCo₃(CO)₈(PR₃ (M^* = Si, Ge). The diastereomers have been resolved in the case of the MePhSi (Obornyl) CCo₃(CO)₉ complex.     

Molecular Recognition and Enantiomer Separations on a novel chiral stationary phase based on a 9,9′-spirobi[9H-fluorene]-derived molecular cleft

An optically active molecular cleft incorporating a 9,9′-spirobi[9H-fluorene] spacer and two N-(5,7-dimethyl-1,8-naphthyridin-2-yl)carboxamide: (CONH(naphthyr)) moieties as H-bonding sites was covalently bound to silica gel to provide the new chiral stationary phase (CSP) (R)- 16 (Scheme 2). Previous solution-binding studies in CDCl₃ had shown that the anchored molecular cleft was capable of complexing optically active dicarboxylic acids with differences in free energy of the formed diastereoisomeric complexes (Δ(ΔG⁰)) between 0.5 and 1.6 kcal mol^?1 (T = 300 K). The optical resolution of racemic dicarboxylic acids, that are bound with a high degree of enantioselectivity in the liquid phase, was now achieved by HPLC on the CSP (R)- 16. The order of enantiomer elution was as predicted from the solution studies, and the separation factor α varied between 1.18 and 1.24. A series of 1,1′-binaphthalene-2,2′-diol derivatives were also resolved on the new CSP, in some cases with baseline separation. The order of enantiomer elution under normal-phase chromatographic conditions was rationalized by computer modeling of the association between the solute enantiomers and the immobilized molecular cleft. HPLC Separations with eluents of different polarity suggested that the attractive interactions between solute and immobilized chiral selector are a combination of H-bonding, which prevails in apolar eluents, and aromatic π--π stacking, which dominates in polar eluents.     

Asymmetric Syntheses XXVI: Catalytic Enantioselective Syntheses of β-Hydroxy Esters via Double Chiral Induction in Asymmetric Reformatsky Reactions

Catalytic asymmetric Reformatsky reactions of benzaldehyde with optically active menthyl bromoacetates in the presence of Zn-Cu couple were performed using 0.25 equiv. of (1R,2S) or (1S,2R)-dimethyl-2-amino-1,2-diphenyl ethanol as chiral ligand to obtain β - hydroxy esters with enantioselectivities up to 60.2%. The obvious double chiral induction effect was observed while chiral ligands matched with optically active substrates.     

An efficient synthesis of optically active (2R,3R)-2-methyl-3-[(1R)-1-methylprop-2-enyl]cyclopentanone, a useful chiral building block for synthesis of vitamin D and steroids

An efficient synthesis of optically active (2R,3R)-2-methyl-3-[(1R)-1-methylprop-2-enyl]cyclopentanone, a useful chiral building block for synthesis of vitamin D and steroids, has been developed starting from readily accessible optically active secondary propargyl phosphate (R)-2, where the asymmetric Michael addition of a chiral allenyltitanium to alkylidenemalonate 3 is a key reaction.     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. VII. Synthese von (3R)-3-Hydroxyretinol, (3R)-3-Hydroxyretinal und (3R)-3-Hydroxyretinsäure

Synthesis of optically active natural carotenoids and structurally related compounds. VII. Synthesis of (3R)-3-hydroxyretinol, (3R)-3-hydroxyretinal and (3R)-3-hydroxyretinoic acid The synthesis of (3R)-3-hydroxyretinol, ( 7 ), (3R)-3-hydroxyretinal ( 9 ) and (3R)-3-hydroxyretinoic acid ( 5 ) according to the building principle C₁₅ + C₅ = C₂₀ is reported utilizing the optically active C₁₅-phosphonium salt 2 and the C₅-aldehyde ester 3 .     

Enantioselective Synthesis of α‐Hydroxy Amides and β‐Amino Alcohols from α‐Keto Amides

Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral Cu^II/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)₃SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)₃SiH to afford the corresponding chiral β‐amino alcohol derivatives.     

Synthesis,characterization, and organocatalytic application of chiral ionic liquids derived from (S,R)-noscapine

(S,R)-Noscapine, a phthalideisoquinoline alkaloid has been used as precursor for the synthesis of chiral ionic liquids (CILs). Noscapine based CILs have been synthesized from reaction between (S,R)-noscapine and methyl iodide in acetonitrile at room temperature. The synthesized CILs have been characterized by ¹H NMR, ¹³C NMR, EI-MS, and polarimetry techniques. These CILs have been used as organocatalysts in the enantioselective reduction of prochiral ketones to produce optically active secondary alcohols. The optically active secondary alcohols have been obtained with excellent yields and low to moderate enantiomeric excess (ee); also the complete enantiomeric excess (100% ee) has been achieved in some cases.     

Syntheses,characterizations, crystal structures,and in vitro antitumor activities of chiral triorganotin(IV) complexes containing (S)-(+)-2-(4-isobutyl-phenyl)propionic and (R)-(+)-2-(4-hydroxyphenoxy)propionic acid ligands

Four new chiral triorganotin(IV) carboxylates, [(R₃Sn)(O₂C₁₃H₁₇)] _n (R?=?Me 1, Ph 2), [(R₃Sn)(O₂C₁₃H₁₇)] (R?=?n-Bu 3), and [(R₃Sn)(O₄C₉H₉)] _n (R?=?Me 4), have been synthesized by reaction of (S)-(+)-2-(4-isobutyl-phenyl)propionic acid and (R)-(+)-2-(4hydroxyphenoxy)propionic acid with triorganotin(IV) chloride in the presence of sodium ethoxide. The complexes have been characterized by elemental analyses, FT-IR, NMR (¹H, ¹³C, and ¹¹⁹Sn) spectra, and X-ray crystallography diffraction analyses. Structural analyses show that 1 has a 1-D infinite chiral zigzag chain structure. Complexes 2 and 4 have a 1-D spring-like chiral helical chain with a channel, while 3 is a monomer. Antitumor activities of 1–4 have been studied.     

C45- und C50-Carotinoide. 4. Mitteilung. Synthese von optisch aktiven cyclischen C20-Bausteinen und von (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotin ( = C.p. 450)

C₄₅- and C₅₀-Carotenoids: Synthesis of Optically Active Cyclic C₂₀-Building Blocks and of (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotene ( = C.p. 450) The synthesis of the optically active C₂₀-building blocks (R)- 26 and (R)- 39 and of the optically active cyclic C₅₀-carotenoid C.p. 450 ( 3 ) starting from (?)-β-pinene is reported.     

(−)-Sparteine: The compound that most significantly influenced my research

A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004     

Ferroelectric Liquid Crystals: Synthesis and Thermal Behavior of Optically Active,Three‐Ring Schiff Bases and Salicylaldimines

The chiral ferroelectric smectic C (SmC*) phase, characterized by a helical superstructure, has been well exploited in developing high‐resolution microdisplays that have been effectively employed in the fabrication of a wide varieties of portable devices. Although, an overwhelming number of optically active (chiral) liquid crystals (LCs) exhibiting a SmC* phase have been designed and synthesized, the search for new systems continues so as to realize mesogens capable of meeting technical necessities and specifications for their end‐use. In continuation of our research work in this direction, herein we report the design, synthesis, and thermal behavior of twenty new optically active, three‐ring calamitic LCs belonging to four series. The first two series comprise five pairs of enantiomeric Schiff bases whereas the other two series are composed of five pairs of enantiomeric salicylaldimines. In each pair of optical isomers, the configuration of a chiral center in one stereoisomer is opposite to that of the analogous center in the other isomer as they are derived from (3 S)‐3,7‐dimethyloctyloxy and (3 R)‐3,7‐dimethyloctyloxy tails. To probe the structure–property correlations in each series, the length of the n‐alkoxy tail situated at the other end of the mesogens has been varied from n‐octyloxy to n‐dodecyloxy. The measurement of optical activity of these chiral mesogens was carried out by recording their specific rotations. As expected, enantiomers rotate plane polarized light in the opposite direction but by the same magnitude. The thermal behavior of the compounds was established by using a combination of optical polarizing microscopy, differential scanning calorimetry, and powder X‐ray diffraction. These complementary techniques demonstrate the existence of the expected, thermodynamically stable, chiral smectic C (SmC*) LC phase besides blue phase I/II (BPI or BPII) and chiral nematic (N*) phase. However, as noted in our previous analogous study, the vast majority of the Schiff bases show an additional metastable, unfamiliar smectic (SmX) phase just below the SmC* phase. Notably, the SmC* phase persists over the temperature range ≈80–115 °C. Two mesogens chosen each from Schiff bases and salicylaldimines were investigated for their electrical switching behavior. The study reveals the ferroelectric switching characteristics of the SmC* phase featuring the spontaneous polarization (P_S) in the range 69–96 nC cm^?2. The helical twist sense of the SmC* phase as well as the N* phase formed by a pair of enantiomeric Schiff bases and salicylaldimines has been established with the help of circular dichroism (CD) spectroscopic technique. As expected, the SmC* and the N* phase of a pair of enantiomers showed mirror image CD signals. Most importantly, the reversal of helical handedness from left to right and vice versa has been evidenced during the N* to SmC* phase transition, implying that the screw sense of the helical array of the N* phase and the SmC* phase of an enantiomer is opposite.     

Synthesis of optically active omeprazole by catalysis with vanadyl complexes with chiral Schiff bases

A new method for the preparation of optically active omeprazole, consisting in asymmetric oxidation of the corresponding sulfide with the use of vanadyl complexes with chiral Schiff bases as the catalysts has been elaborated. The best results of the oxidation were achieved by the use of the combination VO(acac)₂—2-[{(1S,2S,3R,5S)-3-hydroxymethyl-2,6,6-trimethyl-bicyclo[3.1.1]hept-2-ylimino}methyl]phenol—N-ethyl-N,N-diisopropylamine. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1648–1653, August, 2008.     

Asymmetric Photochemical Synthesis of Chiral 5‐(R)‐(l)‐Menthyloxy‐4‐Cycloaminobutyrolactones

Through photocatalysed regiospecific and stereoselective additions of cycloamines to 5‐(R)‐(l)‐menthyloxy‐2 (5H)‐furanone (3), chiral 5‐(R)‐(l)‐menthyloxy‐4‐cycloaminobutyrolactones were synthesized. In the new asymmetric photoaddition of compound 3, the N‐methyl cyclic amines (4) gave novel chiral C? C photoadducts (5) in 24–50% isolated yields with d. e. ≥ 98%. However, the secondary cyclic amines (6) afforded optically active N? C photoadducts (7) in 34–58% isolated yields with d. e. ≥ 98% under the same condition. All the synthesized optically active compounds were identified on the basis of their analytical data and spectroscopic data, such as [α]₅₈₉²⁰, IR, ¹H NMR, ¹³C NMR, MS and elementary analysis. The photosynthesis of chiral butyrolactones and its mechanism were discussed in detail.     

Synthesis of (R)- and (S)-5-(Hydroxymethyl)-3-isopropyloxazolidin-2-one,intermediates in the preparation of optically active β-blockers

The (R)- and (S)-5-(hydroxymethyl)-3-isopropyloxazolidin-2-ones, ((R)- and (S)- 2 , resp.), pivotal intermediates in the preparation of optically active β-blockers, were synthesized using (R,E)-2-hydroxypent-3-enenitrile ( 1 ) as the chiral starting material. In the synthesis of (R)- 2 , a known cyclization/inversion step was applied.     

Editorial

Abstract

Asymmetric syntheses of optically active polymethacrylate, polyacrylate, polyacrylamide, and polyisocyanate with helical conformation and their chiral recognition abilities are described. 1-Phenyldibenzosuberyl methacrylate (PDBSMA) gave a purely onehanded-helical, optically active polymer ([α]₃₆₅ +1670 ～ +1780º) with almost perfectly isotactic structure by anionic polymerization using optically active initiators. Radical polymerizations of PDBSMA using chiral initiators, chain transfer agents, and additives also afforded optically active polymers with a prevailing onehanded helicity. Triphenylmethyl acrylate yielded an optically active, helical polymer ([α]₃₆₅ +102º) having a dyad isotacticity of 70% using an optically active anionic initiator. Although the polyacrylate demonstrated chiral recognition ability as a chiral stationary phase for HPLC, the ability was low mainly because of the low degree of one-handedness. N-(3-Chlorophenyl)-N-phenylacrylamide gave an optically active, helical polymer ([α]_365–343º) in the asymmetric anionic polymerization; the polymer had a dyad tacticity of 77%. Optically active polyisocyanates with a predominantly one-handed helical conformation were prepared in homo-and co-polymerization of optically active phenyl isocyanate derivative. These polyisocyanates showed the ability to discriminate enantiomers in solution.     

Cationic Ir/Me‐BIPAM‐Catalyzed Asymmetric Intramolecular Direct Hydroarylation of α‐Ketoamides

Asymmetric intramolecular direct hydroarylation of α‐ketoamides gives various types of optically active 3‐substituted 3‐hydroxy‐2‐oxindoles in high yields with complete regioselectivity and high enantioselectivities (84–98 % ee). This is realized by the use of the cationic iridium complex [Ir(cod)₂](BAr^F₄) and the chiral O‐linked bidentate phosphoramidite (R,R)‐Me‐BIPAM.     

Twisted Morphologies and Novel Chiral Macroporous Films from the Self‐Assembly of Optically Active Helical Polyphosphazene Block Copolymers

A series of optically active helical polyphosphazene block copolymers of general formula R? [N?P(O₂C₂₀H₁₂)]_n‐b‐[N?PMePh]_m (R‐ 7 a – c ) was synthesized and characterized. The polymers were prepared by sequential living cationic polycondensation of N‐silylphosphoranimines using the mono‐end‐capped initiator [Ph₃P?N?PCl₃][PCl₆] ( 5 ) and exhibit a low polydispersity index (ca. 1.3). The temperature dependence of the specific optical activity ([α]_D) of R‐ 7 a , b relative to that for the homopolymers R‐[N?P(O₂C₂₀H₁₂)]_n (R‐ 8 a ) and the R/S analogues (R/S‐ 7 a , b ), revealed that the binaphthoxy–phosphazene segments induce a preferential helical conformation in the [N?PMePh] blocks through a “sergeant‐and‐soldiers” mechanism, an effect that is unprecedented in polyphosphazenes. The self‐assembly of drop‐cast thin films of the chiral block copolymer R‐ 7 b (bearing a long chiral and rigid R? [N?P(O₂C₂₀H₁₂)] segment) evidenced a transfer of helicity mechanism, leading to the formation of twisted morphologies (twisted “pearl necklace”), not observed in the nonchiral R/S‐ 7 b . The chiral R‐ 7 a and the nonchiral R/S‐ 7 a , self‐assemble by a nondirected morphology reconstruction process into regular‐shaped macroporous films with chiral‐rich areas close to edge of the pore. This is the first nontemplate self‐assembly route to chiral macroporous polymeric films with pore size larger than 50 nm. The solvent annealing (THF) of these films leads to the formation of regular spherical nanostructures (ca. 50 nm), a rare example of nanospheres exclusively formed by synthetic helical polymers.     

C45 und C50-Carotinoide. 6. Mitteilung. Synthese eines optisch aktiven cyclischen C20-Bausteins und von Decaprenoxanthin (= (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-ϵ, ϵ-carotin)

C₄₅- and C₅₀-Carotenoids: Synthesis of an Optically Active Cyclic C₂₀-Building Block and of Decaprenoxanthin ( = (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-?, ?-carotene) The synthesis of the optically active cyclic C₂₀-building block (R, R) -15 and of the optically active C₅₀-carotenoid (2R, 6R, 2′R, 6′R)-decaprenoxanthin ( 1 ) starting from (-)-β-pinene ((S)- 2 ) is reported.     

C45- und C50-Carotinoide. 5. Mitteilung

C₄₅- and C₅₀-Carotenoids. Synthesis of an Optically Active Cyclic C₂₀-Building Block and of (2R,2′S)-3′,4′-Didehydro-1′,2′-dihydro-2-(4-hydroxy-3-methylbut-2-enyl)-2′-(3-methylbut-2-enyl)-β,ψ-caroten-1′-ol (= C. p. 473) The synthesis of the optically active C₂₀-building block (R)- 16 and of the optically active C₅₀-carotenoid C.p. 473 ( 1 ) starting from (?)-β-pinene is reported.