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1.
Due to using (R)‐ or (S)‐α‐methylbenzylamine as a chiral auxiliary, and low‐temperature regime for reduction of the intermediate ferrocenyl‐mono‐ or 1,1′‐bis‐ketimines, the corresponding secondary mono‐ or 1,1′‐bis‐amines were prepared with high diastereoselectivity. Removal of the α‐methylbenzyl group afforded the optically active primary mono‐ and bis‐ferrocenylethylamines in high yields. The absolute configuration of (R,R)‐ 3a and (S,S)‐ 3b was determined by X‐ray single crystal diffraction. 相似文献
2.
The synthesis of novel 2,2‐disubstituted 2H‐azirin‐3‐amines with a chiral amino group is described. Chromatographic separation of the diastereoisomer mixture yielded the pure diastereoisomers (1′R,2R)‐ 4a – e and (1′R,2S)‐ 4a – e (Scheme 1, Table 1), which are synthons for the (R)‐ and (S)‐isomers of isovaline, 2‐methylvaline, 2‐cyclopentylalanine, 2‐methylleucine, and 2‐(methyl)phenylalanine, respectively. The configuration at C(2) of the synthons was determined by X‐ray crystallography relative to the known configuration of the chiral auxiliary group. The reaction of 4 with thiobenzoic acid, benzoic acid, and the dipeptide Z‐Leu‐Aib‐OH ( 12 ) yielded the monothiodiamides 10 , the diamides 11 (Scheme 2, Table 3), and the tripeptides 13 (Scheme 3, Table 4), respectively. 相似文献
3.
The synthesis of novel unsymmetrically 2,2‐disubstituted 2H‐azirin‐3‐amines with chiral auxiliary amino groups is described. Chromatographic separation of the mixture of diastereoisomers yielded (1′R,2S)‐ 2a , b and (1′R,2R)‐ 2a , b (c.f. Scheme 1 and Table 1), which are synthons for (S)‐ and (R)‐2‐methyltyrosine and 2‐methyl‐3′,4′‐dihydroxyphenylalanine. Another new synthon 2c , i.e., a synthon for 2‐(azidomethyl)alanine, was prepared but could not be separated into its pure diastereoisomers. The reaction of 2 with thiobenzoic acid, benzoic acid, and the amino acid Fmoc‐Val‐OH yielded the monothiodiamides 11 , the diamides 12 (cf. Scheme 3 and Table 3), and the dipeptides 13 (cf. Scheme 4 and Table 4), respectively. From 13 , each protecting group was removed selectively under standard conditions (cf. Schemes 5–7 and Tables 5–6). The configuration at C(2) of the amino acid derivatives (1R,1′R)‐ 11a , (1R,1′R)‐ 11b , (1S,1′R)‐ 12b , and (1R,1′R)‐ 12b was determined by X‐ray crystallography relative to the known configuration of the chiral auxiliary group. 相似文献
4.
The chiral compounds (R)‐ and (S)‐1‐benzoyl‐2,3,5,6‐tetrahydro‐3‐methyl‐2‐(1‐methylethyl)pyrimidin‐4(1H)‐one ((R)‐ and (S)‐ 1 ), derived from (R)‐ and (S)‐asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure α‐alkylated (alkyl=Me, Et, Bn) α,β‐diamino acids (R)‐ and (S)‐ 11 – 13 . The chiral lithium enolates of (R)‐ and (S)‐ 1 were first alkylated, and the resulting diasteroisomeric products 5 – 7 were aminated with ‘di(tert‐butyl) azodicarboxylate’ (DBAD), giving rise to the diastereoisomerically pure (≥98%) compounds 8 – 10 . The target compounds (R)‐ and (S)‐ 11 – 13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence. 相似文献
5.
Starting from the enantiomerically pure 2H‐azirin‐3‐amines (R,S)‐ 4 and (S,S)‐ 4 , the enantiomeric, optically active 4‐benzyl‐4‐methyl‐2‐phenyl‐1,3‐thiazole‐5(4H)‐thiones (R)‐ 1 and (S)‐ 1 , respectively, have been prepared (Schemes 2 and 3). In each case, the reaction of 1 with N‐(benzylidene)[(trimethylsilyl)methyl]amine ( 2 ) in HMPA in the presence of CsF and trimethylsilyl triflate gave a mixture of four optically active spirocyclic cycloadducts (Scheme 4). Separation by preparative HPLC yielded two pure diastereoisomers, e.g., (4R,5R,9S)‐ 10 and (4R,5R,9R)‐ 10 . The regioisomeric compounds 11 were obtained as a mixture of diastereoisomers. The products were formed by a 1,3‐dipolar cycloaddition of 1 with in situ generated azomethine ylide 3 , which attacks 1 stereoselectively from the sterically less‐hindered side, i.e., with (R)‐ 1 the attack occurs from the re‐side and in the case of (S)‐ 1 from the si‐side. 相似文献
6.
Jzsef Deli Erzsbet
sz Júlia Visy Ferenc Zsila Mikls Simonyi Gyula Tth 《Helvetica chimica acta》2001,84(1):263-270
The (3R,5′R,6′R)‐ and (3R,5′R,6′S)‐capsanthol‐3′‐one (=3,6′‐dihydroxy‐β,κ‐caroten‐3′‐one; 4 and 5 , resp.) were reduced by different complex metal hydrides containing organic ligands. The ratio of the thus obtained diastereoisomeric (3′S)‐capsanthols 2 and 3 or (3′R)‐capsanthols 6 and 7 , respectively, was investigated. Four complex hydrides showed remarkable stereoselectivity and produced the (3′R,6′S)‐capsanthol ( 6 ) in 80 – 100% (see Table 1). The starting materials and the products were characterized by UV/VIS, CD, 1H‐ and 13C‐NMR, and mass spectra. 相似文献
7.
Four chiral polymers P-1, P-2, P-3 and P-4 were synthesized by the polymerization of (S)-2,2'-dioctoxy-1,1'- binaphthyl-6,6'-boronic acid (S-M-3) with (S)-6,6'-dibromo-1,1'-binaphthol (S-M-1), (R)-6,6'-dibromo-1,1'- binaphthol (R-M-1), (S)-3,3'-diiodo-1,1'-binaphthol (S-M-2) and (R)-3,3'-diiodo-1,1'-binaphthol (R-M-2) under Pd-catalyzed Suzuki reaction, respectively. All four polymers can show good solubility in some common solvents due to the nonplanarity of the polymers in the main chain backbone and flexible alkyl groups in the side chain. The analysis results indicate that specific rotation and circular dichroism (CD) spectral signals of the alternative S-S chiral polymers P-1 and P-3 are larger than those of S-R chiral polymers P-2 and P-4, but their UV-Vis and fluorescence spectra are almost similar. The results of asymmetric enantioselectivity of four polymers for diethylzinc addition to benzaldehyde indicate that catalytically active center is (R) or (S)-1, 1'-binaphthol moieties. 相似文献
8.
Jzsef Deli Erzsbet sz Pter Molnr Ferenc Zsila Mikls Simonyi Gyula Tth 《Helvetica chimica acta》2001,84(12):3810-3817
(6′S)‐ and (6′R)‐‘Capsorubol‐6‐one' (=(3S,3′S,5R,5′R,6′S)‐ and (3S,3′S,5R,5′R,6′R)‐3,3′,6′‐trihydroxy‐κ,κ‐caroten‐6‐one; 8 and 9 , resp.), (6S,6′R)‐ and (6R,6′R)‐capsorubol (=3S,3′S,5R,5′R,6S,6′R)‐ and (3S,3′S,5R,5′R,6R,6′R)‐κ,κ‐carotene‐3,3′,6,6′‐tetrol; 11 and 12 , resp.) and (6′S)‐ and (6′R)‐cryptocapsol (=(3′S,5′R,6′S)‐ and (3′S,5′R,6′R)‐β,κ‐carotene‐3′,6′‐diol; 5 and 6 , resp.) were prepared in crystalline from by the reduction of capsorubin (=(3S,3′S,5R,5′R)‐3,3′‐dihydroxy‐κ,κ‐carotene‐6,6′‐dione; 7 ) and cryptocapsin (=(3′S,5′R)‐3′‐hydroxy‐β,κ‐caroten‐6′‐one; 4 ) and characterized by their UV/VIS, CD, 1H‐NMR, and mass spectra. 相似文献
9.
AnneSophie Droz Ulf Neidlein Sally Anderson Paul Seiler Franois Diederich 《Helvetica chimica acta》2001,84(8):2243-2289
A new family of optically active cyclophane receptors for the complexation of mono‐ and disaccharides in competitive protic solvent mixtures is described. Macrocycles (−)‐(R,R,R,R)‐ 1 – 4 feature preorganized binding cavities formed by four 1,1′‐binaphthalene‐2,2′‐diyl phosphate moieties bridged in the 3,3′‐positions by acetylenic or phenylacetylenic spacers. The four phosphodiester groups converge towards the binding cavity and provide efficient bidentate ionic H‐bond acceptor sites (Fig. 2). Benzyloxy groups in the 7,7′‐positions of the 1,1′‐binaphthalene moieties ensure solubility of the nanometer‐sized receptors and prevent undesirable aggregation. The construction of the macrocyclic framework of the four cyclophanes takes advantage of Pd0‐catalyzed aryl—acetylene cross‐coupling by the Sonogashira protocol, and oxidative acetylenic homo‐coupling methodology (Schemes 2 and 8 – 10). Several cleft‐type receptors featuring one 1,1′‐binaphthalene‐2,2′‐diyl phosphate moiety were also prepared (Schemes 1, 6, and 7). An undesired side reaction encountered during the synthesis of the target compounds was the formation of naptho[b]furan rings from 3‐ethynylnaphthalene‐2‐ol derivatives, proceeding via 5‐endo‐dig cyclization (Schemes 3 – 5). Computer‐assisted molecular modeling indicated that the macrocycles prefer nonplanar puckered, cyclobutane‐type conformations (Figs. 7 and 8). According to these calculations, receptor (−)‐(R,R,R,R)‐ 1 has, on average, a square binding site, which is complementary in size to one monosaccharide. The three other cyclophanes (−)‐(R,R,R,R)‐ 2 – 4 feature, on average, wider rectangular cavities, providing a good fit to one disaccharide, while being too large for the complexation of one monosaccharide. This substrate selectivity was fully confirmed in 1H‐NMR binding titrations. The chiroptical properties of the cyclophanes and their nonmacrocyclic precursors were investigated by circular dichroism (CD) spectroscopy. The CD spectra of the acyclic precursors showed a large dependence from the number of 1,1′‐binaphthalene moieties (Fig. 9), and those of the cyclophanes were remarkably influenced by the nature of the functional groups lining the macrocyclic cavity (Fig. 11). Profound differences were also observed between the CD spectra of linear and macrocyclic tetrakis(1,1′‐binaphthalene) scaffolds, which feature very different molecular shapes (Fig. 10). In 1H‐NMR binding titrations with mono‐ and disaccharides (Fig. 13), concentration ranges were chosen to favor 1 : 1 host−guest binding. This stoichiometry was experimentally established by the curve‐fitting analysis of the titration data and by Job plots. The titration data demonstrate conclusively that the strength of carbohydrate recognition is enhanced with an increasing number of bidentate ionic host−guest H‐bonds (Table 1) in the complex formed. As a result of the formation of these highly stable H‐bonds, carbohydrate complexation in competitive protic solvent mixtures becomes more favorable. Thus, cleft‐type receptors (−)‐(R)‐ 7 and (−)‐(R)‐ 38 with one phosphodiester moiety form weak 1 : 1 complexes only in CD3CN. In contrast, macrocycle (−)‐(R,R,R,R)‐ 1 with four phosphodiester groups undergoes stable inclusion complexation with monosaccharides in CD3CN containing 2% CD3OD. With their larger number of H‐bonding sites, disaccharide substrates bind even more strongly to the four phosphodiester groups lining the cavity of (−)‐(R,R,R,R)‐ 2 and complexation becomes efficient in CD3CN containing 12% CD3OD. Finally, the introduction of two additional methyl ester residues further enhances the receptor capacity of (−)‐(R,R,R,R)‐ 3 , and efficient disaccharide complexation occurs already in CD3CN containing 20% CD3OD. 相似文献
10.
The 2,2′‐methylenebis[furan] ( 1 ) was converted to 1‐{(4R,6S))‐6‐[(2R)‐2,4‐dihydroxybutyl]‐2,2‐dimethyl‐1,3‐dioxan‐4‐yl}‐3‐[(2R,4R)‐tetrahydro‐4,6‐dihydroxy‐2H‐pyran‐2‐yl)propan‐2‐one ((+)‐ 18 ) and its (4S)‐epimer (?)‐ 19 with high stereo‐ and enantioselectivity (Schemes 1–3). Under acidic methanolysis, (+)‐ 18 yielded a single spiroketal, (3R)‐4‐{(1R,3S,4′R,5R,6′S,7R)‐3′,4′,5′,6′‐tetrahydro‐4′‐hydroxy‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐6′‐yl}butane‐1,3‐diol ((?)‐ 20 ), in which both O‐atoms at the spiro center reside in equatorial positions, this being due to the tricyclic nature of (?)‐ 20 (methyl pyranoside formation). Compound (?)‐ 19 was converted similarly into the (4′S)‐epimeric tricyclic spiroketal (?)‐ 21 that also adopts a similar (3S)‐configuration and conformation. Spiroketals (?)‐ 20 , (?)‐ 21 and analog (?)‐ 23 , i.e., (1R,3S,4′R,5R,6′R)‐3′,4′,5′,6′‐tetrahydro‐6′‐[(2S)‐2‐hydroxybut‐3‐enyl]‐7‐methoxyspiro[2,6‐dioxabicyclo[3.3.1]nonane‐3,2′‐[2H]pyran]‐4′‐ol, derived from (?)‐ 20 , were assayed for their cytotoxicity toward murine P388 lymphocytic leukemia and six human cancer cell lines. Only racemic (±)‐ 21 showed evidence of cancer‐cell‐growth inhibition (P388, ED50: 6.9 μg/ml). 相似文献
11.
Roland Kessinger Carlo Thilgen Tiziana Mordasini Franois Diederich 《Helvetica chimica acta》2000,83(12):3069-3096
A series of optically active cis‐3 bis‐adducts, such as (R,R,fC)‐ 16 (Scheme 6), was obtained regio‐ and diastereoselectively by Bingel macrocyclization of C60 with bis‐malonates, which contain optically active tethers derived from 1,2‐diols. The absolute configuration of the inherently chiral addition pattern in cis‐3 bis‐adducts had previously been determined by comparison of calculated and experimental circular dichroism (CD) spectra. Full confirmation of these earlier assignments was now obtained by an independent method based on semiempirical AM1 (`Austin Model 1') and OM2 (`Orthogonalization Method 2') calculations combined with 1H‐NMR spectroscopy. It was found computationally that bis‐malonates [CHR(OCOCH2COOEt)]2, which contain (R,R)‐ or (S,S)‐butane‐2,3‐diol derivatives as optically active tethers, preferentially form out‐out cis‐3 bis‐adducts of C60 as a single diastereoisomer in which the alkyl groups R adopt a gauche conformation, while the two glycolic H‐atoms are in an antiperiplanar (ap) and the ester linkages to the fullerene in a gauche relationship (Figs. 2 and 5). In contrast, in the less favorable diastereoisomer, which should not form, the alkyl groups R adopt an ap and the H‐atoms a gauche conformation, while the ester bridges to the fullerene remain, for geometric reasons, locked in a gauche conformation. According to the OM2 calculations, the geometry of the fully staggered tether in the free bis‐malonates closely resembles the conformation of the tether fragment in the bis‐adducts formed. These computational predictions were confirmed experimentally by the measurement of the coupling constant between the vicinal glycolic H‐atoms in the 1H‐NMR spectrum. For (R,R,fC)‐ 16 , 3J(H,H) was determined as 7.9 Hz, in agreement with the ap conformation, and, in combination with the calculations, this allowed assignment of the fC‐configuration to the inherently chiral addition pattern. This conformational analysis was further supported by the regio‐ and diastereoselective synthesis of cis‐3 bis‐adducts from bis‐malonates, including tethers derived from cyclic glycol units with a fixed gauche conformation of the alkyl residues R at the glycolic C‐atoms. Thus, a bis‐malonate of (R,R)‐cyclohexane‐1,2‐diol provided exclusively cis‐3 bis‐adduct (R,R,fC)‐ 20 in 32% yield (Scheme 7). Incorporation of a tether derived from methyl 4,6‐O,O‐benzylidene‐α‐D ‐glucopyranoside into the bis‐malonate and Bingel macrocyclization diastereoselectively produced the cis‐3 stereoisomer (α,D ,fA)‐ 22 (Scheme 8) as the only macrocyclic bis‐adduct. If the geometry of the alkyl groups R at the glycolic C‐atoms of the tether component deviates from a gauche relationship, as in the case of tethers derived from exo cis‐ and trans‐norbornane‐2,3‐diol or from trans‐cyclopentane‐1,2‐diol, hardly any macrocyclic product is formed (Schemes 5 and 9). The absolute configurations of the various optically active cis‐3 bis‐adducts were also assigned by comparison of their CD spectra, which are dominated by the chiroptical contributions of the inherently chiral fullerene chromophore (Figs. 1, 3, and 4). A strong chiral exciton coupling was observed for optically active macrocyclic cis‐3 bis‐adducts of C60 with two appended 4‐(dimethylamino)benzoate ((S,S,fC)‐ 26 ; Fig. 6) or meso‐tetraphenylporphyrin ((R,R,fC)‐ 28 ; Fig. 7) chromophores. Chiral exciton coupling between two fullerene chromophores was observed for the first time in the CD spectrum of the threitol‐bridged bis‐fullerene (R,R)‐ 35 (Fig. 9). 相似文献
12.
The reactions of 4,4′‐dimethoxythiobenzophenone ( 1 ) with (S)‐2‐methyloxirane ((S)‐ 2 ) and (R)‐2‐phenyloxirane ((R)‐ 6 ) in the presence of a Lewis acid such as BF3?Et2O, ZnCl2, or SiO2 in dry CH2Cl2 led to the corresponding 1 : 1 adducts, i.e., 1,3‐oxathiolanes (S)‐ 3 with Me at C(5), and (S)‐ 7 and (R)‐ 8 with Ph at C(4) and C(5), respectively. A 1 : 2 adduct, 1,3,6‐dioxathiocane (4S,8S)‐ 4 and 1,3‐dioxolane (S)‐ 9 , respectively, were formed as minor products (Schemes 3 and 5, Tables 1 and 2). Treatment of the 1 : 1 adduct (S)‐ 3 with (S)‐ 2 and BF3?Et2O gave the 1 : 2 adduct (4S,8S)‐ 4 (Scheme 4). In the case of the enolized thioketone 1,3‐diphenylprop‐1‐ene‐2‐thiol ( 10 ) with (S)‐ 2 and (R)‐ 6 in the presence of SiO2, the enesulfanyl alcohols (1′Z,2S)‐ 11 and (1′E,2S)‐ 11 , and (1′Z,2S)‐ 13 , (1′E,2S)‐ 13 , (1′Z,1R)‐ 15 , and (1′E,1R)‐ 15 , respectively, as well as a 1,3‐oxathiolane (S)‐ 14 were formed (Schemes 6 and 8). In the presence of HCl, the enesulfanyl alcohols (1′Z,2S)‐ 11 , (1′Z,2S)‐ 13 , (1′E,2S)‐ 13 , (1′Z,1R)‐ 15 , and (1′E,1R)‐ 15 cyclize to give the corresponding 1,3‐oxathiolanes (S)‐ 12 , (S)‐ 14 , and (R)‐ 16 , respectively (Schemes 7, 9, and 10). The structures of (1′E,2S)‐ 11 , (S)‐ 12 , and (S)‐ 14 were confirmed by X‐ray crystallography (Figs. 1–3). These results show that 1,3‐oxathiolanes can be prepared directly via the Lewis acid‐catalyzed reactions of oxiranes with non‐enolizable thioketones, and also in two steps with enolized thioketones. The nucleophilic attack of the thiocarbonyl or enesulfanyl S‐atom at the Lewis acid‐complexed oxirane ring proceeds with high regio‐ and stereoselectivity via an Sn 2‐type mechanism. 相似文献
13.
Pter Molnr Jzsef Deli Ferenc Zsila Andrea Steck Hanspeter Pfander Gyula Tth 《Helvetica chimica acta》2004,87(1):11-27
Violaxanthin A (=(all‐E,3S,5S,6R,3′S,5′S,6′R)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol =syn,syn‐violaxanthin; 5 ) and violaxanthin B (=(all‐E,3S,5S,6R,3′S,5′R,6′S)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol=syn,anti‐violaxanthin; 6 ) were prepared by epoxidation of zeaxanthin diacetate ( 1 ) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I2‐catalyzed photoisomerization. The structure of the main products, i.e., (9Z)‐ 5 , (13Z)‐ 5 , (9Z)‐ 6 , (9′Z)‐ 6 , (13Z)‐ 6 , and (13′Z)‐ 6 , was determined by their UV/VIS, CD, 1H‐NMR, 13C‐NMR, and mass spectra. 相似文献
14.
Diaquapalladium(2+) trifluoromethanesulfonates modified with (4R,4′S)‐ or (4S,4′S)‐2,2′‐bis(4‐benzyl‐4,5‐dihydrooxazole) (Cs‐ and C2‐ligands) produce isotactic poly(1‐oxo‐2‐phenylpropane‐1,3‐diyl) through copolymerization of styrene with carbon monoxide. However, the same meso‐catalyst in the presence of the free ligand leads to prevailingly syndiotactic growth of the copolymer, whereas the optically active catalyst, when used in the presence of the free enantiomeric ligand, gives an atactic copolymer. 相似文献
15.
Silvia Suárez‐Suárez Prof. Gabino A. Carriedo Prof. M. Pilar Tarazona Dr. Alejandro Presa Soto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(18):5644-5653
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. 相似文献
16.
Luca Gobbi Paul Seiler FrancÛois Diederich Volker Gramlich 《Helvetica chimica acta》2000,83(8):1711-1723
The synthesis, characterization, and physical properties of a novel, fully reversible, light‐driven molecular switch, (R,R)‐ 1 /(R,R)‐ 2 , based on a tetraethynylethene‐1,1′‐binaphthalene hybrid system are presented. trans‐Configured (R,R)‐ 1 was synthesized in 57% yield by Stille cross‐coupling between stannylated tetraethynylethene 3 and 3‐iodo‐1,1′‐binaphthalene derivative (R)‐ 4 (cf. Scheme 2). The cis‐isomer (R,R)‐ 2 was prepared from (R,R)‐ 1 by photoisomerization. X‐Ray crystal‐structure analyses were obtained for both cis‐ and trans‐forms of the photoswitch (Figs. 1 and 2). In the crystalline state, molecules of the cis‐isomer (R,R)‐ 2 exhibit intramolecular edge‐to‐face (C−H⋅⋅⋅π) interactions between naphthalene rings of the two 1,1‐binaphthalene moieties (Fig. 3). The switching properties were investigated by electronic absorption spectroscopy (Table and Fig. 4): irradiation at λ=398 nm converts trans‐isomer (R,R)‐ 1 into cis‐isomer (R,R)‐ 2 , whereas switching occurs in the opposite direction upon irradiation at λ=323 nm. No thermal interconversion between the two isomers was observed in CH2Cl2 at room temperature over a period of 2 – 3 months, and the system possesses good resistance against photofatigue (Fig. 5). Investigations of the circular dichroism of (R,R)‐ 1 and (R,R)‐ 2 in CH2Cl2 solution showed that the chiral binaphthalene moieties induce a weak Cotton effect in the achiral tetraethynylethene core (Fig. 6). System (R,R)‐ 1 /(R,R)‐ 2 represents one of the rare switches allowing two‐way photochemical interconversions, not perturbed by thermal‐isomerization pathways. 相似文献
17.
In this paper,a series of new optically active MeO-BIPHEP-type ligands,(S)-6,6'-dimethoxy-2,2'-bis(di-p-alkoxyphenyl-phosphine)-1,1'-biphenyl[(S)-5b—(S)-5e]were prepared and characterized.Starting from thecommercially available triethyl phosphorite and m-bromoanisole,an optically active(S)-6,6'-dimethoxybiphenyl-2,2'-diyl-bis(phosphonic acid diester)was prepared by an improved way and converted to the corresponding dichlo-rides,which was used as a key intermediate to react with p-alkoxybenzenemagnesium bromide or p-alkoxyphenyllithium to directly give the enantiomerically pure diphosphines 5. 相似文献
18.
The absolute configuration of decipinone ( 2 ), a myrsinane‐type diterpene ester previously isolated from Euphorbia decipiens, has been determined by NMR study of its axially chiral derivatives (aR)‐ and (aS)‐N‐hydroxy‐2′‐methoxy‐1,1′‐binaphthalene‐2‐carboximidoyl chloride ((aR)‐MBCC ( 3a ) and (aS)‐MBCC ( 3b )). The absolute configurations at C(7) and C(13) of 2 determined were (R) and (S), respectively. Therefore, considering the relative configuration of 2 , the absolute configuration determined was (2S,3S,4R,5R,6R,7R,11S,12R,13S,15R). 相似文献
19.
Dr. Yosuke Demizu Prof. Mitsunobu Doi Dr. Masaaki Kurihara Prof. Tokumi Maruyama Prof. Hiroshi Suemune Prof. Masakazu Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2430-2439
Chiral cyclic α,α‐disubstituted amino acids, (3S,4S)‐ and (3R,4R)‐1‐amino‐3,4‐(dialkoxy)cyclopentanecarboxylic acids ((S,S)‐ and (R,R)‐Ac5cdOR; R: methyl, methoxymethyl), were synthesized from dimethyl L ‐(+)‐ or D ‐(?)‐tartrate, and their homochiral homoligomers were prepared by solution‐phase methods. The preferred secondary structure of the (S,S)‐Ac5cdOMe hexapeptide was a left‐handed (M) 310 helix, whereas those of the (S,S)‐Ac5cdOMe octa‐ and decapeptides were left‐handed (M) α helices, both in solution and in the crystal state. The octa‐ and decapeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2‐trifluoroethanol solution. The left‐handed (M) helices of the (S,S)‐Ac5cdOMe homochiral homopeptides were exclusively controlled by the side‐chain chiral centers, because the cyclic amino acid (S,S)‐Ac5cdOMe does not have an α‐carbon chiral center but has side‐chain γ‐carbon chiral centers. 相似文献
20.
VíctorManuel Gutirrez‐García Gloria Reyes‐Rangel Omar Muoz‐Muiz Eusebio Juaristi 《Helvetica chimica acta》2002,85(12):4189-4199
Inexpensive acryloyl chloride was converted in 91% overall yield to two derivatives of β‐alanine, (R,R,R)‐ 6 and (R,R,S)‐ 6 , containing two chiral auxiliaries. C‐Alkylation of (R,R,R)‐ and (R,R,S)‐ 6 via a dianion derivative, was performed by direct metallation with 2.2 equiv. of lithium hexamethyldisilazane (LHMDS) in THF at ?78°. C‐Alkylation of (R,R,S)‐ 6 ‐Li2 (‘matched' pair of chiral auxiliaries) afforded the mono‐alkylated products 8 – 11 in 29–96% yield and 54–95% stereoselectivity. Employment of LiCl as an additive generally increased stereoselectivities, whereas the effect of HMPA as a cosolvent was erratic. Chemical correlation of the major diastereoisomer from the alkylation reactions with (S)‐α‐alkyl‐β‐alanine ( 12 – 15 ) showed that addition of the electrophile preferentially takes place on the enolate's Si‐face. This conclusion is also supported by molecular‐modeling studies (ab initio HF/3‐21G), which indicate that the lowest‐energy conformation for (R,R,S)‐ 6 ‐Li2 presents the more sterically hindered Re‐face of the enolate. The theoretical studies also predict a determining role for N? Li? O chelation in (R,R,S)‐ 6 ‐Li2, giving rise to an interesting ‘ion‐triplet' configuration for the dilithium dianion. 相似文献