Total synthesis of (+)-SCH 351448

Total synthesis of SCH 351448 was accomplished employing the ring-closing olefin metathesis reaction for the preparation of the 28-membered macrodiolide.     

Assignment of absolute configuration to SCH 351448 via total synthesis

The synthesis and absolute configuration of SCH 351448, an interesting ionophoric natural product, are reported herein. Mukaiyama aldol-Prins and segment-coupling Prins reactions were employed to construct the constituent tetrahydropyrans of SCH 351448. Efforts to assemble the C2-symmetric core of the natural product by a templated olefin metathesis strategy are described; however, a stepwise fragment assembly was ultimately utilized to complete the target molecule.     

Synthesis of the proposed structure of feigrisolide C

[reaction: see text] Possible structures of feigrisolide C were synthesized via ring-closing olefin metathesis reaction of a diester derivative prepared from 8-epi-nonactic acid, but physical characteristics of the synthetic samples did not match with those of the natural sample of feigrisolide C.     

A formal synthesis of SCH 351448

An efficient formal synthesis of SCH 351448 was accomplished through the tandem cross-metathesis (CM)/oxa-Michael, the 1,4-syn aldol, the tandem oxidation/oxa-Michael, and the Suzuki coupling reaction.     

Mutual influence of oligoolefins,oligodienes, and bisoligoisobutenylsuccinimide,modified with sulfur and phenols,in model systems

The mutual influence of olefin and diene oligomers and bisoligoisobutenylsuccinimide, functionalized with sulfur and phenols, in model oil formulations in evaluation of their solubilizing effect and antioxidant activity was examined. The solubilizing power of the synthesized water-and-oil-soluble surfactant, sodium salt of oligomeric sulfur-containing phenol, in the presence of small concentrations of water was evaluated.     

Syntheses and structures of rhenium(IV) and rhenium(V) complexes with ethanedithiolato ligands

A novel dimeric rhenium(IV) complex, [Re2(SCH2CH2S)4], and a monomeric methyloxorhenium(V) complex, [CH3ReO(SCH2CH2S)PPh3], were synthesized from methyloxorhenium(V) complexes and characterized crystallographically. The structure of [Re2(SCH2CH2S)4], the formation reaction of which showed surprising demethylation conceivably through the homolytic cleaveage of the rhenium-carbon bond, features distorted trigonal prismatic coordination of sulfurs around the metal center and a rhenium-rhenium triple bond. A revised structure, [Tc2(SCH2CH2S)4], is proposed for a related technetium complex, originally identified as [Tc2(SCH2CH2S)2(SCH=CHS)2] (Tisato et al. Inorg. Chem. 1993, 32, 2042). Additionally, a new compound, CH3Re(O)(SPh)2PPh3, was prepared.     

BINOL Aza Macrocycle Derivatives: Synthesis of Dinaphthosulfone Aza Macrocycles Using p-Toluenesulfonic Acid (p-TsOH) in Methanol as an Efficient Route and Evaluation of Their 1H NMR Spectra

Dinaphthosulfone aza macrocycles were synthesized from the reaction of diamines and dinaphthosulfone diester (1,1′-sulfoxobis-(2-naphthoxy(2-methyl acetate))) in methanol in the presence of catalytic amounts of para toluenesulfonic acid (p-TsOH). Dinaphthosulfone diester (1,1′-sulfoxobis-(2-naphthoxy(2-methyl acetate))) was synthesized from the corresponding dinaphthosulfide diester and hydrogen peroxide in formic acid at room temperature. Dinaphthosulfide diester was prepared from initial dinaphtholsulfide diol (1,1′-thio bis(2-hydroxy naphthalene)) and methylchloroacetate. ¹H NMR spectroscopy showed the unusual splittings for these dinaphthosulfone aza macrocycles, and this finding could be proposed as the role of tetrahedral structure of sulfone functional group, hydrogen bonding in the cavity and size of macrocycle.     

Dicobaltoctacarbonyl-mediated synthesis of tricyclic 5,6-diydropyran-2-one derivatives via tandem cycloaddition reaction between cis-epoxyalkynes, a tethered olefin, and carbon monoxide

Cobalt carbonyl complex Co2(CO)8 implemented an intramolecular carbonylation of cis-epoxyalkynes to generate Co2(CO)6-stabilized gamma-lactonyl allene species. For 1,1,2-trisubstituted epoxyalkynes, this Co2(CO)6-allene species reacted with a tethered olefin to give [2+2]-cycloadducts, and with CO and a tethered olefin to produce [2+2+1]-cycloadducts. These resulting cycloadducts have a 5,6-diydropyran-2-one core fused with a cyclobutane and a cyclopentanone ring, respectively. For 1,2-disubstituted cis-epoxyalkyne and 1,1,2-trisubstituted cis-epoxyalkynes bearing a heteroatom constituent, cyclization of the corresponding epoxyalkyne with a tethered alkene is invariably accompanied by incorporation of CO to produce a [2+2+1]-cycloadduct, even in the absence of CO. We have prepared various 1,1,2-trisubstituted and 1,2-disubstituted cis-epoxyalkynes to generalize such cycloaddition pathways. Attempt to use an organic promoter to perform these tandem cycloadditions was unsuccessful because of a competing Pauson-Khand reaction. Cyclization of a 1,2-disubstituted epoxyalkyne with a tethered diene was achieved successfully in one case, but the yield was low (25%).     

Approaches to the Synthesis of Cytochalasans. Part 11. Further transformations and cyclization attempts directed towards proxiphomin

Starting from iodoalcohol 9 , the monoprotected dialdehyde 5 was synthesized (Scheme 2) and converted to 17 by reaction with oxo-phosphonate 15 (Scheme 3). The latter was prepared from 13 . Cyclisation of 17 to the target compound 18 failed. Also the attachment of thiol 22 to lactone 19 was unsatisfactory (Scheme 4). Therefore, the building blocks 28 and 29 were synthesized using diene 33 and diester 30 as starting material for 28 and 9 for 29 (Scheme 5 and 6). Hydroxy acid 28 was converted into formyl-ester 46 (Scheme 7). However, the condensation of its derivatives 48 and 49 with ‘Umpolung’ of the carbonyl reactivity was unsuccessful, probably due to steric hindrance.     

Synthesis of the C1-C21 (C1'-C21') fragment of the dimeric polyketide natural product SCH 351448

[structure: see text] A convergent, stereoselective assembly of the C1-C21 (C1'-C21') fragment of SCH 351448, a 28-membered bis-lactone natural product, has been developed. A highly efficient approach to this fragment assembles 75% of the carbon skeleton and all the stereochemical elements present in the natural product. In addition, an interesting boron ligand effect on the diastereoselectivity of a key aldol reaction with methyl ketone-derived enolborinates is reported.     

草酸钙的结晶动力学及不同种类羧酸盐的影响

通过检测体系中游离Ca2+离子浓度及草酸钙(CaOxa)的粒径随时间的变化,研究了CaOxa的结晶动力学及3种羧酸盐对CaOxa结晶动力学的影响,这些羧酸盐为:一元羧酸盐甘氨酸钠(NaGlu)、二元羧酸盐酒石酸钠(Na2Tart)和三元羧酸盐柠檬酸三钠(Na3Cit)。在生理盐水中CaOxa的结晶动力学方程为r=kc3.3±0.3,平均反应速率常数(k)为(3.1±1.8)×109;3种抑制剂对k的影响程度从大到小为:Na3Cit>Na2Tart>NaGlu,但其平均反应级数(α)相差不大,α=3.2±0.1。Na3Cit、Na2Tart可抑制CaOxa晶体的生长和聚集过程,是潜在的肾结石抑制剂。     

Intramolecular [4 + 2] cycloaddition of nitroalkenes for construction of vicinal quaternary stereocenters

[chemical reaction: see text]. Nitroalkene (E)-1 has been synthesized to test the feasibility of an intramolecular [4 + 2] cycloaddition in a planned synthesis of daphnilactone B. This nitro olefin contains two unique structural features, a nitromethylene lactone and a pendant diene, that combine under the action of SnCl4 in a highly selective fashion to afford nitronates 2a and 2b. These products represent the correct relationship for the vicinal quaternary stereogenic centers in the core of daphnilactone B.     

水热法Fe-Mn催化剂制备及其合成气制低碳烯烃催化活性

以水热合成法制备了K原位改性的Fe-Mn催化剂,考察了其CO加氢合成低碳烯烃催化活性。采用SEM、TEM、XRD、H₂-TPR和FT-IR等手段对催化剂进行了表征。结果表明,制备的催化剂前驱体呈50~70 nm的球形颗粒,表面富含羰基和羟基,物相组成以Fe₃O₄为主,用于反应后有Fe₅C₂和MnCO₃相生成。与共沉淀法制备催化剂相比,在设定的反应条件下,不同K含量改性的催化剂均具有较高的活性,以原料配比Fe:Mn:C₆:K=3:1:5:0.10的催化剂性能最佳,CO转化率达95.02%,总低碳烯烃收率为62.86 g/m³(H₂+CO),CH₄和CO₂选择性分别为13.88%和13.98%。     

Synthesis and Crystal Structure of a Complex Bimetallic Salt [Ni(trans_[14]diene)] [Ni (mnt)_2]

1INTRoDUCTIONMacrocycliccoordinationcomPOundshavebeenwidelyinvestigatedinthepastdecadesbecauseoftheirrelationshiptocomplexesofbiologicalsignificancesuchasthePorphyrinsandcorrins(lJ.Structuresofmanymacrocycliccompoundshavebeenre-ported,especiallythecompoundscontainingN4macrocyclicligands"'.However,toourknowledge,onlyafewcrystalstructuresofcomplexbimetallicsaltscontainingmacrocyclicligandshavebeendeterminedbyX-raydiffractionmethod.Inthispa-per,werePortthesynthesisandstructureofthetit1ecom…     

New epoxy-terminated oligoesters: Precursors to totally biodegradable networks

Two types of novel biodegradable epoxy resins, carrying cycloaliphatic-epoxy and glycidyl ester end-groups, have been synthesized from hydroxy-telechelic oligoesters. The cycloaliphatic-epoxy end-groups were based on either methyl cis-4-cyclohexene-2-(carboxylic acid)-1-carboxylate or 3-cyclohexene-1-carboxylic acid. These compounds were reacted with hydroxy-telechelic poly(ε-caprolactone-co-D ,L -lactide) oligoesters, yielding cycloaliphatic-olefin-terminated oligomers. Conversion of the olefin to the epoxide groups was achieved using a phase transfer epoxidation with an inorganic peracid derived from the reaction of phosphoric acid, sodium tungstate, and hydrogen peroxide. Aliquat 336, a quaternary ammonium salt, acted as the phase transfer catalyst. Nearly theoretical conversion of hydroxy to epoxy end-groups was achieved in only one case, however, alternative variations of this method of synthesis show promise. To prepare glycidyl ester-terminated prepolymers, hydroxy-telechelic poly(ε-caprolactone) oligoesters were reacted with succinic anhydride, in 1,2-dichloroethane with 1-methylimidazole as catalyst, resulting in (carboxylic acid)-terminated oligomers. After conversion of the end-groups to the potassium carboxylate salt by titration with methanolic KOH, the isolated salt was dried and reacted with epibromohydrin in acetonitrile at reflux, using an 18-C-6 crown ether as the phase transfer catalyst, thus preparing the (glycidyl ester)-telechelic prepolymer. Epoxide equivalent weights differed by 2.7–7.1% from the theoretical values. These cycloaliphatic-epoxide and glycidyl ester-terminated prepolymers may be crosslinked with anhydrides or amines, respectively, to produce totally bioabsorbable networks. © 1993 John Wiley & Sons, Inc.     

Total synthesis of (+)-SCH 351448

A convergent synthesis of (+)-SCH 351448 (1), a monosodium salt of a C(2)-symmetric macrodiolide, is described. Our approach is based on a [4 + 2] annulation with a chiral allyl silane (anti-5c) to assemble the pyran subunits. Homodimerization was carried out in a stepwise fashion; initial esterification at C29' followed by macrocyclization at C29 afforded the desired macrodiolide.     

A theoretical study for the regioselective Diels–Alder reaction of 5,6‐fulleroid with strained anti‐Bredt olefins

Regioselectivity of Diels–Alder reaction of the anti‐Bredt olefin of fulleroid, the 5,6‐methylene‐bridged fullerene derivative, is theoretically clarified by DFT calculations. In transition state calculations, the addition of a noncyclic diene 2,3‐dimethyl‐1,3‐butadiene (DMBD) at the anti‐Bredt olefin has considerably lower activation energy than those at the other sixteen olefins, while the reaction of a rigid cyclic diene cyclohexadiene (CHD) has similar activation energy at both anti‐Bredt and another nontwisted olefin. The changes in strain and interaction of the reactants are estimated along its reaction coordinate by activation strain model. Noncyclic diene shows asynchronous C? C bond formation with a significant gain of interaction energy, while the rigid cyclic diene shows a large growth of strain energy canceling out the interaction energy between diene and fulleroid.     

Graft copolymerization induced by thermal reactions of the binary alkali salts of poly(carboxylic acid)–brominated carboxylic acid in bulk

Thermal reactions of the binary alkali salts of poly(carboxylic acid)–brominated carboxylic acid such as sodium or potassium poly(4-vinylbenzoate)-2-bromopropanoate [Na or K (PVBA-2-BPA)] in bulk were investigated. A methanol solution of binary acids was prepared by fixing the molar ratio of the repeating unit of polymeric acid to the fraction of brominated carboxylic acid. The binary salts were prepared by the neutralization of the binary acid solution. The product of the thermal reaction followed by esterification was identified as a graft copolymer containing PVBA in the main chain and polylactic acid in the side chain. The reaction of 1/15 K (PVBA-2-BPA) at 120 °C for 2 h yielded the highest percentage of grafting (300%). The grafting proceeded gradually for the initial 2 h and then somewhat. Reactivity of the K salt was higher than that of the corresponding Na salt. The thermal reaction of 1/10 K [polymethacrylate-2-BPA (PMA-2-BPA)] at 120 °C for 2 h also yielded a graft copolymer, and the percentage of grafting was 300%. However, reaction temperatures higher than 120 °C caused homopolycondensation of K 2-BPA prior to grafting, and homopolycondensation occurred prior to grafting in the reaction with Na (PMA-2-BPA). © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1877–1885, 2001     

Stereoselective hydrogenation of conjugate diene directed by hydroxy group and asymmetric synthesis of deoxypolypropionate units

Optically active cyclic compounds carrying a conjugate diene and two hydroxy groups were prepared through the intramolecular Büchner reaction with a chiral tether and succeeding stereoselective conversion. Hydrogenation of the diene in the first step was not regioselective but resulted in three regioisomeric monoenes. Nevertheless, the final saturated product carrying two stereogenic centers could be obtained in 98% stereochemical purity on further hydrogenation under optimized conditions. The high stereoselectivity throughout the multiple pathways is attributable to the effective direction by the hydroxy group. Ring cleavage of the produced stereochemically pure seven-membered ring compounds successfully resulted in synthetic intermediates for deoxypolypropionates.     

Lipase-catalyzed kinetic resolution of cyclic trans-1,2-diols bearing a diester moiety: synthetic application to chiral seven-membered-ring alpha,alpha-disubstituted alpha-amino acid

Chiral cycloalkane-trans-1,2-diols (+/-)-3 and (+/-)-8 having a diester moiety have been prepared from dimethyl dialkenylmalonate using olefin metathesis by Grubbs catalyst, followed by epoxidation and acidic hydrolysis. Kinetic resolution of racemic cyclopentane-trans-1,2-diol (+/-)-3 by lipase-catalyzed transesterification afforded an optically active monoacetate (-)-5 of 95% ee in 46% yield and the recovered diol (-)-3 of 92% ee in 51% yield, and that of cycloheptane-trans-1,2-diol (+/-)-8 gave a monoacetate (+)-10 of 95% ee in 51% yield and the diol (-)-8 of >99% ee in 43% yield, respectively. The enantiomer selectivity of racemic cyclic trans-1,2-diols bearing a diester moiety by lipases (Amano PS and Amano AK) was opposite to that of the reported simple racemic cycloalkane-trans-1,2-diols. To explain the lipase-catalyzed enantiomer selectivity, computer modeling of lipase-substrate complexes was performed. Furthermore, the optically active diester (-)-8 could be efficiently converted into an optically active seven-membered-ring alpha,alpha-disubstituted amino acid (4R,5R)-(-)-15.