Synthesis of (E)- and (Z)-α,β-difluorourocanic acid

Horner-Emmons fluoroolefination of an aryl aldehyde followed by introduction of a second fluorine via “FBr” addition provides an original approach to the preparation of 1-alkyl-2-aryl-1,2-difluoroethenes. The utility of this procedure is demonstrated by the preparation of (E and Z)-α,β-difluorourocanic acid.     

亚稳碘化汞(β-HgI2M)晶体生长与相变

采用溶液法,以α-HgI₂为原料,在DMSO和H₂O混合溶剂中生长了β-HgI₂^M晶体。通过XRD检测了晶体的结构特征,利用偏光显微镜研究了晶体生长的动态过程及β-HgI₂^M→α-HgI₂的相变过程。研究表明,生长的晶体为β-HgI₂^M,空间结构为Cmc2₁;晶体生长界面夹角为65.02°,与β-HgI₂^M单胞中(110)和(110)夹角(65.16°)吻合;β-HgI₂^M→α-HgI₂相变为结构重构的一级相变。     

亚稳碘化汞(β-HgI2M)晶体生长与相变

采用溶液法,以α-HgI_2为原料,在DMSO和H_2O混合溶剂中生长了β-HgI_2~M晶体。通过XRD检测了晶体的结构特征,利用偏光显微镜研究了晶体生长的动态过程及β-HgI_2M→α-HgI_2的相变过程。研究表明,生长的晶体为β-HgI_2~M,空间结构为Cmc2_1;晶体生长界面夹角为65.02°,与β-HgI_2~M单胞中(110)和(110)夹角(65.16°)吻合;β-HgI_2~M→α-HgI_2相变为结构重构的一级相变。     

Temperature-dependent molecular-recognizable membranes based on poly(N-isopropylacrylamide) and β-cyclodextrin

A novel temperature-dependent molecular-recognizable membrane, poly(N-isopropylacylamide-co-glycidyl methacrylate/cyclodextrin)-grafted-polyethylene terephthalate (P(NIPAM-co-GMA/CD)-g-PET) membrane, is prepared by the combination of plasma-induced pore-filling grafting polymerization and chemical reaction. Scanning electron microscope (SEM) images show that the surfaces and cross-sections of the prepared membranes are uniformly grafted by polymeric layer. Fourier transform infrared (FT-IR) results show that CDs are successfully induced onto the P(NIPAM-co-GMA) grafted chains through reaction with epoxy groups. When the environmental temperature increases from 25 °C to 45 °C, the contact angle of prepared P(NIPAM-co-GMA/CD)-g-PET membrane increases from 65° to 76.9°; whereas, that of substrate membrane decreases from 84.8° to 77.1°. During the dynamic adsorption experiments, the guest 8-anilino-1-naphthalenesulfonic acid ammonium salt (ANS) molecules are adsorbed onto the P(NIPAM-co-GMA/CD)-g-PET membrane at lower temperature (25 °C) and desorbed from it at higher temperature (40 °C) with good repeatability. This phenomenon of adsorption at low temperature and desorption at high temperature of the P(NIPAM-co-GMA/CD)-g-PET membrane is attributable to both the “swollen–shrunken” configuration change of P(NIPAM-co-GMA) grafted chains and the molecular recognition of CD toward ANS. The P(NIPAM-co-GMA/CD)-g-PET membrane show both good thermo-responsibility and temperature-dependent molecular-recognizable characteristics toward guest molecules, which is highly potential to be applied in temperature-controlled affinity separations.     

Palladium-catalyzed stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrenes: straightforward access to (Z)-α-fluorocinnamic aldehydes and (Z)-β-fluorocinnamic alcohols

We report here the stereoconvergent formylation of (E/Z)-β-bromo-β-fluorostyrene mixtures with carbon monoxide and sodium formate catalyzed by palladium. Optimization of reaction conditions leads to the corresponding pure (Z)-α-fluorocinnamaldehydes in good yields. The reaction was extended to styrenes bearing electro-attracting or electro-donating groups. The obtained α-fluoroaldehydes were smoothly reduced to the corresponding (Z)-β-fluorocinnamic alcohol by NaBH(4). The reaction could be performed on functionalized substrates as demonstrated by the access to the glucoside of β-fluoroconiferyl alcohol, (Z)-β-fluoroconiferin, a strong inhibitor of lignin polymerization.     

A practical and efficient synthesis of (E)-β-aryl-α,β-unsaturated amides

In this paper, we report a one-step convergent synthesis of (E)-β-monosubstituted α,β-unsaturated amides 3 from α-sulfonyl acetamide 1 and benzyl bromide derivatives 2.     

BF3·Et2O-catalyzed rearrangement of 7-epimeric 3β,7-diacetoxy-9β,11β-epoxy-5α-lanostanes. Formation of novel 19(10→9β)abeo- and 19(10→9β), 30(14→8α)bis-abeo-lanostane derivatives

The boron trifluoride etherate catalyzed reaction of 7-epimeric 3β,7-diacetoxy-9β,11β-epoxy-5α-lanostanes 1 and 2 in acetic anhydride resulted in the formation of a series of skeletally rearranged products, mainly 19(10→9β)abeo-lanostanes. 19(10→9β),30(14→8α)Bis-abeo-lanostane derivative 5 possessing a novel type of the triterpene skeleton was formed as the major product in the reaction of 7α-epimer 2. The direction and extent of rearrangements of 9β,11β-epoxides 1 and 2 depends on the configuration of the 7-acetoxy group. The structures of the new compounds were determined on the basis of spectroscopic methods, mainly ¹H and ¹³C NMR. The structure of compound 5 was confirmed by single-crystal X-ray diffraction.     

Facile synthesis of (Z)- and (E)-3-allylidene-β-lactams via thermal β-elimination of trans-3-allyl-3-sulfinyl-β-lactams

A competent synthetic route for the synthesis of novel (Z)- and (E)-3-allylidene-β-lactams is described. The strategy involves oxidation of trans-3-allyl-3-phenylthio-β-lactams 1 using sodium metaperiodate (NaIO₄) to diastereomeric trans-3-allyl-3-phenylsulfinyl-β-lactams 2 and 3, which further undergo thermal β-elimination in refluxing carbon tetrachloride to furnish (Z)- and (E)-3-allylidene-β-lactams 5 and 6 in good to excellent yields. The molecular structure of 3b has been established with the help of single crystal X-ray analysis.     

Synthesis of α-amino-β-keto-esters (β-oxodipeptides)

The synthesis of α-amino-β-keto-esters (β-oxo dipeptides) was studied. Corresponding α-amino-β-ketoesters were prepared from BOC-(L)-Valine and BOC-(L)-isoleucine by coupling with (D,L)-threonine hydrochloride and oxidation with Dess-Martin periodinane (DMP) with a total yield of 48% and 38%, respectively. __________ Translated from Chemistry Online, 2007, 70(10): 793–796 [译自: 化学通报]     

Room temperature preparation of α-chloro-β,β-difluoroethenylzinc reagent (CF2CClZnCl) by the metallation of HCFC-133a (CF3CH2Cl) and a high yield one-pot synthesis of α-chloro-β,β-difluorostyrenes

α-Chloro-β,β-difluorovinylzinc reagent [CF₂CClZnCl] was generated in 91% yield by the metallation of a THF solution of commercially available HCFC-133a (CF₃CH₂Cl) and zinc chloride at 15-20 °C using LDA as base. The corresponding reaction with Halothane™ (CF₃CHClBr) produced a poor yield of CF₂CClZnCl. The palladium catalyzed coupling reaction of the CF₂CClZnCl with aryl iodides under mild reaction conditions produced α-chloro-β,β-difluorostyrenes in 64-90% isolated yields. The stability of the intermediate CF₂CClLi and the nature of the zinc reagents are discussed.     

两例配位聚合物[MCl2(β-ala)]n(M=Co,Ni;β-ala=3-氨基丙酸)的结构相变

利用3-氨基丙酸（β-ala）和过渡金属氯化物构筑了2例互为异质同晶的配位聚合物[MCl₂（β-ala）]_n（M=Co²⁺ （1）,Ni²⁺ （2））,并通过差示扫描量热法、变温X射线单晶衍射以及变温介电测试研究了它们的结构相变。配合物1和2的结构中,相邻的M²⁺离子通过2个氯离子和1个双齿羧基的桥联作用形成一维配位链。在升/降温过程中,1和2分别在236、224 K和309、302 K附近发生高温相（Pnam）与低温相（Pna2₁）之间的温致结构相变;该相变主要是由配体的铵乙基由高温相中的两重无序状态冻结为低温相中的有序状态而引起的,该有序-无序型相变使这两个化合物在相变温度附近都表现出介电台阶及介电弛豫的共存现象。     

Synthesis of a chito-tetrasaccharide β-1,4-GlcNAc-β-1,4-GlcN repeating unit

Abstract  

tert-Butyldimethylsilyl (4-O-acetyl-2-azido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl)-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside (Kawada and Yoneda [MOCHEM-D-09-00120], 2009), designed as a repeating disaccharide unit in a β-glucan having two different faces, was converted into a glycosyl donor and an acceptor. The glycosyl acceptor was glycosylated with the donor to afford a chito-tetrasaccharide derivative in good yield. Phthalimido and azido groups in the tetrasaccharide were successively converted into acetamido and free amino groups, and all other protecting groups were cleaved to obtain the chito-tetrasaccharide (2-amino-2-deoxy-β-d-glucopyranosyl)-(1 → 4)-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1 → 4)-(2-amino-2-deoxy-β-d-glucopyranosyl)-(1 → 4)-2-acetamido-2-deoxy-d-glucopyranose.     

The dienolate aldol reaction of (E)-N-crotonoyl C(4)-isopropyl SuperQuat: asymmetric synthesis of α-vinyl-β-hydroxycarboxylic acid derivatives and conversion to α-ethylidene-β-hydroxyesters (β-substituted Baylis-Hillman products)

The synthesis of α-vinyl-β-hydroxyesters and α-ethylidene-β-hydroxyesters (β-substituted Baylis-Hillman products) via the dienolate aldol reaction of (E)-N-crotonoyl C(4)-isopropyl SuperQuat is described. High levels of syn-diastereoselectivity (up to >98% de) are observed for the dienolate aldol reaction with boron enolates, generated either directly with Bu₂BOTf or by transmetalation of the potassium enolate with B-bromocatecholborane. Cleavage of the resultant syn-aldol products from the auxiliary gives α-vinyl-β-hydroxyesters in >98% de and >98% ee. Subsequent isomerisation of the double bond into conjugation provides α-ethylidene-β-hydroxyesters (β-substituted Baylis-Hillman products) in high diastereo- and enantiopurity (≥91:9 [(E):(Z)] and >98% ee).     

Physical-mechanical properties of Zr-(Re)-doped β-rhombohedral boron

Effect of doping with Zr(Re) on the structure and physical-mechanical properties of β-rhombohedral boron has been studied. In all specimens p-type conductivity was found. Internal friction and dynamic shear modulus of the specimens were investigated at frequencies of torsion oscillations (0.5-5 Hz) in the temperature range 80<T<1000 K. The increase of Zr(Re) concentration in the samples results in increase of their hole concentration, this increasing and shifting the observed IF maxima to lower temperatures; activation energy of the maxima and frequency factor of the relaxation processes decrease by 10-15%. Effects of change of the structure-sensitive properties observed in Zr-(Re)-doped boron are analyzed in view of changes of activation energy necessary for the motion of twinning boundaries and stacking faults.     

A novel strategy toward the synthesis of N-(β-glycosyl)asparagines based on the alkylation of ethyl nitroacetate using N-(β-glycosyl)iodoacetamides

A conceptually novel strategy has been developed for the synthesis of N-(β-glycosyl)asparagine precursors in good yield by the alkylation of ethyl nitroacetate using six per-O-acetylated N-(β-glycosyl)iodoacetamides derived from mono- and disaccharides. The use of a chiral organocatalyst, N-(9-anthracenylmethyl)cinchoninium chloride (10 mol %), resulted in diastereoselective alkylation up to 64% de. Single crystal structure analysis of the purified major diastereomer of the Glc derivative revealed an absolute configuration of S at the α-carbon of the monosubstituted ethyl nitroacetate which is a precursor of the l-asparagine conjugate.     

Synthesis of ( )-5α-Hydroxy-β-selinene and (-)-5β-Hydroxy-β-selinene

Eudesmanederivativeshavebeendrawingconsiderableattentionduetotheirwidespectrumofbiologicalproperties,particularlyantifeedant,cellgroWthinhibitoryandplantgroWthregulatingactivitiesl'2.Recently,twoepimericeudesmanederivatives( )-5a-hydroxy-6-selinene1and(-)-56-hydroxy-6-selinene2wereisolated3fromtheaerialpartsofCSubtraPicaFMell.,andtheirstructuresweredeterminedbyspectroscopicmethods.Herein,wereportafacilesynthesisofbothtwodiastereomers1and2from( )-dihydrocarvone3infivesteps,usingtheregioselect…     

SiCl4-catalyzed/PR3-mediated β-C(sp3)−H functionalization of nitrones to α,β-unsaturated imines and aromatic heterocycles

A novel method of SiCl₄-catalyzed/PR₃-mediated β-C(sp³)?H functionalization of nitrones with aldehydes/ketones to α,β-unsaturated imines was developed. The synthesis of α,β-unsaturated imines mainly invovles deoxygenation and aldol condensation, each proceeding under a cooperation effect between Lewis acid and Lewis base. In addition, both the acidity and hydrolytic stability of the weak SiCl₄ were supposed to be enhanced by coordination with phosphine oxide (R?=?Et) or phosphoric triamide (R?=?NMe₂) that originated from deoxygenation of nitrones by PR₃. In the case of 6-membered nitrone, a [1,3]-hydride shift within the resulted α,β-unsaturated imines renders the aromatization leading to 3,5-dialkylpyridines.