Enantioselective addition of diethylzinc to aldehydes catalyzed by β‐amino alcohols derived from (1R,2S)‐norephedrine

β‐Amino alcohols derived from (1R,2S)‐norephedrine were synthesized and used as ligands in the catalytic enantioselective diethylzinc addition to benzaldehydes. N‐alkylated (1R,2S)‐norephedrine‐based derivative 3a gave the highest enantioselectivity. The effects of different parameters on the enantioselectivity of the product were investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of N4‐substituted[1,3,4]oxadiazinan‐2‐ones derived from norephedrine

[1,3,4]‐Oxadiazinan‐2‐ones bearing substitution at the N₄‐position have been synthesized from norephedrine in good yield via N‐alkylation, nitrosation, reduction and cyclization.     

(1R,2R)‐2‐(4‐Methylenecyclohex‐2‐enyl)propyl (1R,4S)‐camphanate

Esterification of a single diastereomer of 2‐(4‐methylene­cyclohex‐2‐enyl)propanol, (II), with (1R,4S)‐(+)‐camphanic acid [(1R,4S)‐4,7,7‐trimethyl‐3‐oxo‐2‐oxabicyclo[2.2.1]heptane‐1‐carboxylic acid] leads to the crystalline title compound, C₂₀H₂₈O₄. The relative configuration of the camphanate was determined by X‐ray diffraction analysis. The outcome clarifies the relative and absolute stereochemistry of the naturally occurring bisabolane sesquiterpenes β‐turmerone and β‐sesquiphellandrene, since we have converted (II) into both natural products via a stereospecific route.     

Synthesis and α‐Mannosidase Inhibitory Evaluation of (2R,3R,4S)‐ and (2S,3R,4S)‐2‐(Aminomethyl)pyrrolidine‐3,4‐diol Derivatives

The synthesis of 46 derivatives of (2R,3R,4S)‐2‐(aminomethyl)pyrrolidine‐3,4‐diol is reported (Scheme 1 and Fig. 3), and their inhibitory activities toward α‐mannosidases from jack bean (B) and almonds (A) are evaluated (Table). The most‐potent inhibitors are (2R,3R,4S)‐2‐{[([1,1′‐biphenyl]‐4‐ylmethyl)amino]methyl}pyrrolidine‐3,4‐diol ( 3fs ; IC₅₀(B)=5 μM , K_i=2.5 μM ) and (2R,3R,4S)‐2‐{[(1R)‐2,3‐dihydro‐1H‐inden‐1‐ylamino]methyl}pyrrolidine‐3,4‐diol ( 3fu ; IC₅₀(B)=17 μM , K_i=2.3 μM ). (2S,3R,4S)‐2‐(Aminomethyl)pyrrolidine‐3,4‐diol ( 6 , R?H) and the three 2‐(N‐alkylamino)methyl derivatives 6fh, 6fs , and 6f are prepared (Scheme 2) and found to inhibit also α‐mannosidases from jack bean and almonds (Table). The best inhibitor of these series is (2S,3R,4S)‐2‐{[(2‐thienylmethyl)amino]methyl}pyrrolidine‐3,4‐diol ( 6o ; IC₅₀(B)=105 μM , K_i=40 μM ). As expected (see Fig. 4), diamines 3 with the configuration of α‐D ‐mannosides are better inhibitors of α‐mannosidases than their stereoisomers 6 with the configuration of β‐D ‐mannosides. The results show that an aromatic ring (benzyl, [1,1′‐biphenyl]‐4‐yl, 2‐thienyl) is essential for good inhibitory activity. If the C‐chain that separates the aromatic system from the 2‐(aminomethyl) substituent is longer than a methano group, the inhibitory activity decreases significantly (see Fig. 7). This study shows also that α‐mannosidases from jack bean and from almonds do not recognize substrate mimics that are bulky around the O‐glycosidic bond of the corresponding α‐D ‐mannopyranosides. These observations should be very useful in the design of better α‐mannosidase inhibitors.     

(−)‐(1R,2S,2′R,5R)‐2‐(1‐Hydroxyprop‐2‐yl)‐5‐methylcyclohexanol

Stereoselective hydroboration of (?)‐isopulegol and subsequent fractional crystallization furnishes the title compound, C₁₀H₂₀O₂. The relative configuration of the stereogenic centres has been assigned by means of X‐ray diffraction analysis since the monoterpenediol is employed as a versatile chiral building block in stereospecific natural product synthesis.     

A pair of diastereomeric 1:1 salts of (S)‐ and (R)‐2‐methylpiperazine with (2S,3S)‐tartaric acid

The structures of diastereomeric pairs consisting of (S)‐ and (R)‐2‐methylpiperazine with (2S,3S)‐tartaric acid are both 1:1 salts, namely (S)‐2‐methylpiperazinium (2S,3S)‐tartrate dihydrate, C₅H₁₄N₂²⁺·C₄H₄O₆²⁻·2H₂O, (I), and (R)‐2‐methylpiperazinium (2S,3S)‐tartrate dihydrate, C₅H₁₄N₂²⁺·C₄H₄O₆²⁻·2H₂O, (II), which reveal the formation of well defined ammonium carboxylate salts linked via strong intermolecular hydrogen bonds. Unlike the situation in the more soluble salt (II), the alternating columns of tartrate and ammonium ions of the less soluble salt (I) are packed neatly in a grid around the a axis, which incorporates water molecules at regular intervals. The increased efficiency of packing for (I) is evident in its lower `packing coefficient', and the hydrogen‐bond contribution is stronger in the more soluble salt (II).     

Multigram Solution‐Phase Synthesis of Three Diastereomeric Tripeptidic Second‐Generation Dendrons Based on (2S,4S)‐, (2S,4R)‐, and (2R,4S)‐4‐Aminoprolines

Three diastereomeric second‐generation (G2) dendrons were prepared by using (2S,4S)‐, (2S,4R)‐, and (2R,4S)‐4‐aminoprolines on the multigram scale with highly optimized and fully reproducible solution‐phase methods. The peripheral 4‐aminoproline branching units of all the dendrons have the 2S,4S configuration throughout, whereas those units at the focal point have the 2S,4S, 2S,4R, and 2R,4S configurations. These latter configurations led to the dendrons being named (2S,4S)‐ 1 , (2S,4R)‐ 1 , and (2R,4S)‐ 1 , respectively. The 4‐aminoproline derivatives used in this study are new, although many closely related compounds exist. Their syntheses were optimized. The dendron assembly involved amide coupling, the efficiency of which was also optimized by employing the following well‐known reagents: EDC/HOBt, DCC/HOSu, TBTA/HOBt, TBTU/HOBt, BOP/HOBt, pentafluorophenol, and PyBOP/HOBt. It was found that the use of PyBOP is by far the best for dendrons (2S,4S)‐ 1 and (2R,4S)‐ 1 , and pentafluorophenol active ester is best for (2S,4R)‐ 1 . Because of their multigram scale, all couplings were done in solution instead of by solid‐phase procedures. Purifications were, nevertheless, easy. The optical purities of the key intermediates as well as the three G2 dendrons were analyzed by chiral HPLC analysis. These novel, diastereomeric second‐generation dendrons have a rather compact and conformationally highly rigid structure that makes them interesting candidates for applications, for example, in the field of dendronized polymers and in organocatalysis.     

Tetrakis(μ‐triisopropylsilanethiolato)‐1:2κ4S:S;2:3κ4S:S‐bis(triisopropylsilanethiolato)‐1κS,3κS‐trizinc(II)

The title compound, [Zn₃(C₉H₂₁SiS)₆] or [(ⁱPr₃SiS)Zn(μ‐SSiⁱPr₃)₂Zn(μ‐SSiⁱPr₃)₂Zn(SSiⁱPr₃)], is the first structurally characterized homoleptic silanethiolate complex of zinc. A near‐linear arrangement of three Zn^II ions is observed, the metals at the ends being three‐coordinate with one terminally bound silanethiolate ligand. The central Zn^II ion is four‐coordinate and tetrahedral, with two bridging silanethiolate ligands joining it to each of the two peripheral Zn^II ions. The nonbonding intermetallic distances are 3.1344 (11) and 3.2288 (12) Å, while the Zn...Zn...Zn angle is 172.34 (2)°. A trimetallic silanethiolate species of this type has not been previously identified by X‐ray crystallography for any element.     

A pair of diastereomeric 1:2 salts of (R)‐ and (S)‐2‐methylpiperazine with (2S,3S)‐tartaric acid

The crystal structures of a pair of diastereomeric 1:2 salts of (R)‐ and (S)‐2‐methylpiperazine with (2S,3S)‐tartaric acid, namely (R)‐2‐methylpiperazinediium bis[hydrogen (2S,3S)‐tartrate] monohydrate, (I), and (S)‐2‐methylpiperazinediium bis[hydrogen (2S,3S)‐tartrate] monohydrate, (II), both C₅H₁₄N₂²⁺·2C₄H₅O₆⁻·H₂O, each reveal the formation of well‐defined head‐to‐tail‐connected hydrogen tartrate chains; these chains are linked into a two‐dimensional sheet via intermolecular hydrogen bonds involving hydroxy groups and water molecules, resulting in a layer structure. The (R)‐2‐methylpiperazinediium ions lie between the hydrogen tartrate layers in the most stable equatorial conformation in (I), whereas in (II), these ions are in an unstable axial position inside the more interconnected layers and form a larger number of intermolecular hydrogen bonds than are observed in (I).     

Efficient synthesis of B-alkylated oxazaborolidines derived from ephedrine and norephedrine

[reaction: see text] Representative B-butyl- and B-methyl-1,3,2-oxazaborolidines derived from ephedrine and norephedrine were prepared in good yield and excellent purity by one-pot treatment of B-H oxazaborolidines with the corresponding organolithium reagent and subsequent hydrolysis of the cyclic borohydride intermediate with anhydrous ammonium chloride.     

(1R,2R,3S,4S)‐2‐[(2R,3S)‐2,3‐Di­methyl­oxiran‐2‐yl]‐3,4‐bis(4‐methoxy­benzyl­oxy)­cyclo­hexanol

The relative configuration was determined for the title com­pound, C₂₆H₃₄O₆, which was prepared in a synthetic study on immunosuppressant FR­65­814. There is an intra­mol­ecular hydrogen bond between the hydroxy and epoxy groups.     

(1S,2R,2′S)‐ and (1S,2S,2′S)‐1‐phenyl‐2‐phenyl­thio‐2‐(tetra­hydro­pyran‐2′‐yl­thio)­ethanol diastereoisomers at 193 K

In the synthesis of 1‐phenyl‐2‐phenyl­thio‐2‐(tetra­hydro­pyran‐2‐yl­thio)­ethanol, C₁₉H₂₂O₂S₂, four diastereoisomers are formed. Two non‐centrosymmetric enantiomeric forms which crystallize in space groups P2₁2₁2₁ and Pna2₁ are presented. The former has an intramolecular hydrogen bond between the hydroxyl group and the O atom of the tetra­hydro­pyran ring. In the latter isomer, the hydroxyl group forms an intermolecular hydrogen bond to the O atom of the tetra­hydro­pyran­yl group of a neighbouring mol­ecule, joining the mol­ecules into chains in the c‐axis direction; the O?O distances are 2.962 (4) and 2.764 (3) Å, respectively. The tetra­hydro­pyran rings are in chair conformations in both isomers and the S side chain has an equatorial orientation in the former, but an axial orientation in the latter mol­ecule.     

Chiral Liquid Crystals Synthesized from 2(S)‐[2(R)‐Methylhexyloxy]Propanol and its (S,S)‐Diastereomer

Two new chiral alcohols, 2(S)‐[2(R)‐methylhexyloxy]propanol ( 5 ) and 2(S)‐[2(S)‐methylhexyloxy]propanol ( 6 ), were prepared from the corresponding propionic acid ethyl ester 1 and 2 in the presence of sodium borohydride. They were used as the chiral moiety for the synthesis of two diastereomeric liquid crystals 7 and 8 . Both of them exhibit the phase sequence I‐SmA‐SmC*‐SmX‐Cr. The mesogenic properties of the (S,S)‐diastereomer 8 are more unique in comparison with those of the (S,R)‐diastereomer 7. It possesses not only lower SmA and SmC* phase transition temperature, 103 °C vs. 112 °C for SmA phase and 31 °C vs. 65 °C for SmC* phase, but wider SmA and SmC* phase range, 40 °C vs. 31 °C for SmA phase and 72 °C vs. 47 °C for SmC* phase. The diastereomer 8 also has a larger Ps value than that of 7, 24 vs. 15 nC cm^?2 measured at Tc ‐ T = 10 °C. The difference in these mesogenic properties is discussed by comparing their conformation difference at the molecular part of benzoate.     

Poly(ethylene terephthalate) copolyesters derived from (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol

Novel poly(ethylene terephthalate) (PET) copolyesters, abbreviated PEDMBT, containing optically active (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol (DMBD) as the second comonomer were investigated. Copolymers with ethylene glycol to DMBD ratios between 95/5 and 50/50 as well as the two parent homopolymers, PET and PDMBT, were prepared by a two‐step melt polycondensation. The resulting copolymers were found to approximately have the composition of the polymerization reaction feed and a random microstructure. Polymer intrinsic viscosities varied from 0.4 to 0.6 dL g^?1 with weight‐average molecular weights ranging from 16,000 to 44,000. PEDMBT copolyesters were distinguished in being much more soluble than PET and showing an increasing affinity for water with the content in dimethoxy groups. According to the asymmetric constitution of DMBD, they displayed optical activity in solution. Both melting and glass‐transition temperatures of the copolyesters were observed to steadily decrease with the content in DMBD. PEDMBTs were found to be crystalline for contents in DMBD up to 30 mol %. Both powder and fiber X‐ray diffraction revealed that the same crystalline structure is shared by PET and the crystalline copolyesters. The homopolyester PDMBT resulted in becoming a polymer with a crystallinity comparable to PET but with a significantly different crystalline structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3250–3262, 2001     

Synthesis of New C2‐Symmetric Chiral Bisamides from (1S,2S)‐Cyclohexane‐1,2‐dicarboxylic Acid

A series of new C₂‐symmetric (1S,2S)‐cyclohexane‐1,2‐dicarboxamides was synthesized from (1S,2S)‐cyclohexane‐1,2‐dicarbonyl dichloride and N‐benzyl‐substituted aromatic amines, which were prepared from 2‐aminopyridine, 2‐chloroaniline, and 2‐aminophenol via imine formation with benzaldehyde and subsequent reduction with NaBH₄. (1S,2S)‐N,N′‐Dibenzyl‐N,N′‐bis[2‐(benzyloxy)phenyl]cyclohexane‐1,2‐dicarboxamide was converted to (1S,2S)‐N,N′‐dibenzyl‐N,N′‐bis(2‐hydroxyphenyl)cyclohexane‐1,2‐dicarboxamide via hydrogenolysis in the presence of Pd(OH)₂ on active carbon powder.     

Synthesis of 1,3,4‐oxa(or thia)diazaheterocycles starting from 2‐(pyrrol‐1'‐y1)phthalimide

1‐(1,3‐Dioxo‐1,3‐dihydro‐2H‐isoindol‐2‐yl)‐1H‐pyrrol‐2 carbaldehyde 4 was synthesized by Vilsmeier‐Haack reaction from 2‐(pyrrol‐1‐yl) phthalimide. Reduction of 4 by sodium borohydride, or action of Grignard reagents on 4 led to the corresponding alcohols 5 which were cyclized to pyrroloxadiazino isoin‐doles 1 by heating in the presence of silica gel. Transformation of the hydroxylactam 6 with acetic acid derivatives led to the esters 7 which gave, after saponification, pyrroloxa(or thia)diazepinoisoindolones 2 by intramolecular cyclization.     

Synthesis of indole and indolenine derivatives starting from indoline‐2‐thiones

Indoline‐2‐thiones 1a‐b,d,f,h , which have at least one hydrogen at the 3‐position reacted with α‐halo ester 2a‐d , α‐halo ketones 2e‐f , and a‐bromoacetonitrile 2g to give 2‐alkylthioindole derivatives 3–11 . In a similar manner treatment of 3,3‐disubstituted indoline‐2‐thiones 1c,e with α‐halo esters 2a,c,d and α‐halo ketone 2e gave 2‐alkylthioindolenines 12–16 . Treatment of 1,3,3‐ trisubstituted indoline‐2‐thiones 1g,i with ethyl bromo‐acetate 2a resulted in recovery of starting materials. Desulfurization of indolenine 14 with triphenylphosphine gave 2‐alkylideneindoline 19 .     

Bis(tetraphenylphosphonium) (hexasulfido‐2κ2S1,S6)di‐μ‐sulfido‐disulfido‐1κ2S‐tungsten(VI)zinc(II) acetone solvate

The title complex, (C₂₄H₂₀P)₂[WZnS₄(S₆)]·C₃H₆O or (Ph₄P)₂[WS₂(μ‐S)₂{Zn(S₆)}]·Me₂CO, was unexpectedly obtained on attempted recrystallization of a mixed tungten–zinc complex of a tris(pyrazolato)borate ligand. The two metal centres of the anion have distorted tetrahedral coordination and the two tetrahedra share one S...S edge; tungsten is additionally coordinated by two terminal sulfide ligands and zinc by a chelating S₆²⁻ ligand, which has one central S—S bond significantly longer than the other four, a pattern found to be consistent for this ligand. This is the first reported example of a tetrahedral zinc centre bridging an edge of a single tetrathiotungstate(VI) or tetrathiomolybdate(VI) anion, although there are many previous examples with other metals.     

Synthesis,Characterization, and Herbicidal Activities of New 1,3,4‐Oxadiazoles, 1,3,4‐Thiadiazoles,and 1,2,4‐Triazoles Derivatives Bearing (R)‐5‐Chloro‐3‐fluoro‐2‐phenoxypyridine

Synthesis of some novel 1,2,4‐triazoles, 1,3,4‐oxadiazoles and 1,3,4‐thiadiazoles bearing a (R) 5‐(1‐(4‐(5‐chloro‐3‐fluoropyridin‐2‐yloxy)phenoxy)ethyl) unit, as a moiety of commercial herbicide, using their thiosemicarbazides in an alkaline, iodine and acidic media is reported, respectively. The structure of the synthesized compounds was characterized by IR, ¹H, ¹³C NMR spectroscopic data, and elemental analyses. The herbicidal activities of synthesized compounds were evaluated against Echinochloa cruss‐galli, Avena fatua, and Sorgum halepense weeds. Compounds 7 and 12a showed potential herbicidal activity against gramineous weeds. Our results may provide some guidance for synthesis development of some novel oxa or thiadiazole and triazole‐based herbicidal lead structures.