bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of 1‐[(3‐Halo‐1‐Hydroxy‐2‐Propoxy)methyl]uracil and Thymine as Potential Antiviral Agents
Authors: Wang Eng‐Chi , Chen Hour‐Young , Tzeng Cherng‐Chyi 
Published: May 2015

Abstract3′‐Halogen acyclonucleoside analogs have been prepared. The starting material, benzyl glycidyl ether (5), prepared from eplchlorohydrin and sodium benzyloxidc, underwent ring opening by soft halogen ions to give l‐benzyloxy‐3‐fluoro‐2‐propanol (6), l‐bcnzyloxy‐3‐chloro‐2‐propanol (7), and l‐benzyloxy‐3‐ bromo‐2‐propanol (8) respectively. The treatment of 5 with lithium iodide in the presence of acetic acid provided 1‐benzyloxy‐3‐iodo‐2‐propanol (9). The treatment of 8 with sodium iodide in anhydrous acetone also produced l‐benzyloxy‐3‐iodo‐2‐propanol (9). Chloromethylation of these halohydrins 6‐9 using paraformaldehyde and hydrogen chloride gas produced the chloromcthyl ethers 10‐13. These chloromethyl ethers without further purification were allowed to react with the silylated bases 16‐17, previously prepared by silylating the bases 14‐15 with HMDS in the presence of ammonium sulfate to give 1‐ [(l‐benzyloxy‐3‐halogen‐2‐propoxy)methyl]uracils and thymines 19‐25. The target compounds 26‐33 were obtained respectively after the debcnzylation of 18‐25. Compounds 26, 27, 30 and 31 had no significant cell toxicity in the range of concentrations 0.001‐20 mM. Compounds 26, 27, 28 and 29 have no significant activity against HSV II (for less than 2 mM there is a cytopathic effect). Compounds 30, 31, 32 and 33 show no activity against HSV II virus even at the level 20 mM.
Constituents of Clinopodium Umbrosum
Authors: Lee Shu‐Mei , Lai Jeng‐Shiow , Kuo Yueh‐Hsiung 
Published: May 2015

AbstractThe isolation and identification of fifteen crystalline components from the whole herb of Clinopodium umbrosum (Bieb.) C. Koch (Labiatae) are described. Their structures were determined on the basis of spectral evidence and chemical transformation. These compounds include five steroids (α‐spinasterone, β‐sitosterol, stigmasterol, α‐spinasterol, and α‐spinasteryl‐3‐O‐β‐glucopyranoside), four triterpenoids (3β‐hydroxyurs‐11‐en‐28,13‐olide, betulinic acid, oleanolic acid, ursolic acid), four flavonoids (luteolin, luteolin‐7‐O‐β‐glucopyranoside, apigenin‐7‐O‐β‐glucuronide, and apigenin‐7‐O‐β‐methylglucuronate), and two lignolic acids [3‐(3,4‐dihydroxyphenyl)‐ lactic acid and rosmarinic acid].
Synthesis of 4‐Arylpyridines Containing Electron‐Withdrawing Groups on the Benzene Ring
Authors: Shiao Min‐Jen , Liu Kang‐Hsiuan , Wang Jy‐Shih 
Published: May 2015

Abstract4‐Arylpyridines 5 that contain electron‐withdrawing groups such as nitrile, methyl ester, fluoride, and trifluoromethyl on the benzene ring were synthesized in moderate yields (29‐63%) by reaction of mixed copper, zinc aryl organometallics 1 with various 1‐(ethoxycarbonyi)pyridinium chlorides 2 followed by o‐chloranil oxidization under reflux in toluene.
The Mean Isomer Degeneracy of the Wiener Index
Authors: Gutman Ivan , Luo Ycung‐Long , Lee Shyi‐Long 
Published: May 2015

AbstractThe mean isomer degeneracy of the Wiener index was previously shown to become unboundedly large as n (the number of vertices of the molecular graphs of the isomers considered) increases. We here show that there is a high isomer degeneracy in the case of molecules of medium size, namely when n = 6 and n = 7.
Exchange Charges and Bond Orders for Homonuclear Diatomic Molecules
Authors: Chang Tse‐Chiang 
Published: May 2015

AbstractA new bond order definition B = βS2 is defined which relates the bond order B to the non‐classical exchange charges in the bonding region. This definition is successful in correlating the bond order to its bond energy, when the overlap is calculated from a generalized valence‐bond pair function and the parameter β is chosen to be the inverse of bond distance.
Aspergillus Protease‐Catalyzed Esterification at pH > 7
Authors: Tai Dar‐Fu , Chiu Li‐Chun , Huang Ching Chong , Liaw Wen‐Cheng 
Published: May 2015

AbstractDiverse N‐substituted amino acids were converted to their corresponding esters by crude sucrose‐immobilized Aspergillus oryzae protease in organic solvents at pH 7.5. The front part of captopril S‐(‐)‐acetylthio‐2‐methylpropionic acid and the aspartame precursor Cbz‐L‐Asp‐L‐Phe‐OH also underwent esterification under such conditions.
Indirect Determination of Sulfate by Atomic Absorption Spectrophotometry
Authors: Chang Chur‐Min , Huang Hsuan‐Jung 
Published: May 2015

AbstractWith a flow injection technique, the content of sulfate in solution was determined indirectly from the concentration of partially equilibrated barium ion in solution. To obtain improved sensitivity, atomic absorption spectrophotometry of a flame was used to determine barium. With these procedures combined with a linear calibration graph, superior sensitivity and detection limit of sulfate determination were obtained compared with those from other indirect methods.
Proton Nuclear Magnetic Resonance Measurements of 2′‐Aminodeoxyuridylyl‐3′,5′‐Deoxyuridine
Authors: Kan Lou‐Sing , Bauman Rick , Bhan Purshotam , Miller Paul S. 
Published: May 2015

AbstractA dideoxyribonucleotide, 2′‐amino‐2′‐deoxyuridylyl 3′,5′‐deoxyuridine, containing an unsual base (2′‐amino‐2′‐deoxyuridine) that isresistant to nucleases was investigated by ′H NMR. The pKa of the protonation of the amino group (5.8) was determined by profiles of chemical shifts of protons in the vicinity of amino group versus pH. However, protonation of the amino group has little effect on the conformation of the dimer, assumed to be B‐form DNA. This conclusion is drawn from the chemical shift data and coupling constants of H1‐H2. Thus, 2′‐amino‐2′‐deoxyuridine can be used in antisense and anticode oligonucleotides.
Photochemistry of Syn‐ and Anti‐A8,9‐Dimethoxycarbonyl‐1,5‐Dipropyl‐3‐Oxatricyclo[3.2.2.02,4]Non‐8‐Ene‐6,7‐Dione
Authors: Liao Chun‐Chen , Lin Ho‐Shen , Tsai Yow‐Fu , Ueng Yih‐Gang 
Published: May 2015

AbstractIn the photochemistry of the title compounds, the anti isomer 6 afforded oxepine 9 whereas the syn isomer yielded 9 and 10; the reactions proceeded partly via cyclobutanediones 12 and 13. The distinct photochemical behavior are explained in terms of stereorelectronic effects of the epoxy rings.
Thermal Decomposition of Fluorinated Dioxolane Carboxylates
Authors: Hung Ming‐H. , Famham Willia M. B. 
Published: May 2015

AbstractSynthesis of fluorodioxole olefin monomers by thermal decomposition of fluorinated dioxolane carboxylic acid and the corresponding acyl chloride was explored. Complex product formation is observed, including acyl fluoride from Cl‐F exchange, the hydro‐dioxolane from proton abstraction, the cyclic ether ketone from dioxolane ring opening, and the epoxy acid fluoride from thermal rearrangement. The product distribution is strongly dependent upon reaction conditions. The main influential factors include the reaction temperature, the base used for the reaction, the presence or absence of solvent, and the counter ion associated with the intermediate salt. A mechanism is proposed to rationalize both the results and the product distribution. Methods to make authentic samples for product analysis are reported.
The Reaction of 4‐Formylsydnone with Nitroalkanes
Authors: Hung Wei‐Jing , Tien Hsien‐Ju , Yu Hsien‐Cheng 
Published: May 2015

AbstractUnder various basic solutions and reaction durations, 3‐substituted 4‐formyIsydnones and nitroalkanes containing α‐active hydrogen (e.g. nitromethane and nitroethane) are converted to β‐nitroalcohols, nitroalkenes and dinitroalkanes. β‐Nitroalcohols are obtained only by electrochemical reaction on an electrogenerated base (EGB). The mechanism of overall reaction steps in particular is discussed.
An Exchange Charge Model for Covalent Bonds in Simple Homonuclear Diatomic Molecules
Authors: Chang Tse‐Chiang 
Published: May 2015

AbstractThe point charge in Parr's simple bond charge model is replaced by the exchange charge, which can be evaluated according to a simple ab initio method. The calculated exchange charge correlate well with the experimental values of force constants and dissociation energies for homonuclear diatomic molecules H2, Li2, F2, Na2 and Cl2.
Constituents of the Heartwood of Diospyros Eriantha
Authors: Chen Chien‐Chih , Yu Hsi‐Jung , Ou Jun‐Chih , Pan Tzu‐Ming 
Published: May 2015

AbstractThe isolation and identification of fifteen compounds from the heartwood of Diospyros eriantha are described. Their structures were determined on the basis of spectral evidence and/or comparison with authentic samples. These compounds include three steroids (stigmast‐4‐en‐3‐one, stigmast‐4‐ene‐3,6‐dione, and 3β‐hydroxystigmast‐5‐en‐7‐one), seven triterpenoids (friedelin, lupeol, betulinaldehyde, 3β‐acetoxyurs‐11‐en‐13,28‐olide, 3β‐acetoxyoleanolic acid, betulin, and betulinic acid), three quinones (2‐ethoxy‐7‐methyljuglone, 3‐ethoxy‐7‐methyljuglone, and 2,6‐dimethoxy‐1,4‐benzoquinone), and two phenols (3,4,5‐trimethoxyphenol, and syringic acid).
New Pseudostationary Phases for Electrokinetic Chromatography: A High‐Molecular Surfactant and Proteins
Authors: Terabe Shigeru , Ozaki Hiroto , Tanaka Yoshihide 
Published: May 2015

AbstractTo extend the applicability of electrokinetic chromatography (EKC), two new types of pseudostationary phases have been introduced. A high‐molecular surfactant, butyl acrylate/butyl methacrylate/methacrylic acid copolymer (BBMA) is employed as a micellar forming surfactant for miccllar electrokinetic chromatography (MEKC). The critical micelle concentration of BBMA is essentially zero, which means the micellar concentration is constant irrespective of temperature and buffer. Some characteristic features of BBMA as the pseudostationary phase for MEKC is investigated in comparison with conventional ionic surfactants. Ovomucoid and avidin, which are proteins isolated from egg white, have been found to be useful chiral selectors in affinity EKC. A few examples of the separation of enantiomers with these proteins are shown.
Uncharged Co(lll) Complexes: Transfer Chemical Potentials and Base Hydrolysis in Water‐Methanol Mixtures
Authors: Abu‐Gharib Ezz‐Eldin A. 
Published: May 2015

AbstractSolubilities are reported for three Co(III) complexes of 2‐aminophenol, 2‐amino‐4‐nitrophenol and 6‐amino‐2,4‐dimethylphenol. Transfer chemical potentials have been derived from appropriate solubility measurements in aqueous methanol. The trends in transfer chemical potentials are discussed in terms of the nature of the coordinated ligands and are compared with those for selected of other inorganic Co(III) complex ions. The kinetics of base hydrolysis of Co(III) complexes in aqueous methanol solutions are described and the change in the activation barrier δmΔG≠ is determined. Solvent effects on reactivity trends are analysed into initial state and transition state components. The small decrease in the rate constant, with increasing proportion of methanol, is ascribed to a greater effect of solvent on the initial state.
Mixed Valence Chemistry of Pyrimidine Bridged Binuclear Complex of Pentacyanoferrate and Pentaammineruthenium
Authors: Tsaur Grace , Wu Ming‐Chu , Yen Andrew 
Published: May 2015

AbstractThe pyrimidine bridged binuclear complex (CN)5FepymRu(NH3)5‐ (I) was prepared in aqueous solution by mixing cquimolar of Fe(CN)5OH23− and Ru(NH3)5pym2+. Its mixed valence state molecule (CN)5FepymRu(NH3)5(II) was obtained upon oxidation of I by one equivalent of peroxydisulfate ion. Both binuclear complexes and corresponding Fe(II) and Ru(II) mononuclear complexes displayed a metal‐to‐ligand charge transfer absorption in 400–450 nm region. Rate constants of formation and dissociation of I and II were measured, and the values of kf (−103M−1s−1) and kd (−10−3‐10−4 s−1) were consistent with kinetic results expected for the substitution of Fe(CN)5OH23− with di‐ and trivalent ligands. Cyclic voltammetry of I exhibited two one‐electron steps of oxidation corresponding to [III, L, II] + e → [II, L, II] and [III, L, III] + e → [III, L, II], respectively. The mixed valence binuclear complex II showed an intervalence band at 955 nm with a molar extinction coefficient 5.80 × 102 M−1cm−1 and a half‐width 5100 cm−l. The properties of the IT band conform to Hush's theory. Spectroscopic, electrochemical and kinetic results of II suggest that the mixed valence complex features a trapped ‐ valence formulation with localized oxidation states of Fe(II) and Ru(III).
Hydrogen Chloride Induced Reorganization of Packing Phases in Self‐assembled Monolayers of n‐Alkanoic Acids on Silver Surface
Authors: Tao Yu‐Tai , Ma Li‐Fang 
Published: May 2015

AbstractA unique reorganization process, which was induced by HCI treatment of the self‐assembled monolayers of n‐alkanoic acids on silver surfaces, was visualized by polarized reflection absorption IR spectroscopy. The process can be reversible or irreversible, depending on the chain length of the monolayer‐forming acid. Thus for C16 acid, the highly oriented and crystalline monolayer packing phase reorganized reversibly into isotropic microcrystallites. For C8 acid, the ordered packing phase reorganized irreversibly into a disordered, liquid‐like phase. For C24 acid, reversible change in orientation occurred. All changes are due to the protonation‐deprotonation reaction occurring at the binding head group.
Monosubstituted Trinuclear and Tetranuclear VIB Metal Carbonyl Complexes: Syntheses of [{M(CO)5}3(Pf‐Pf‐Pf)] [Pf‐Pf‐Pf = PhP(CH2CH2PPh2)2] and [{M(CO)5}4(P‐Pf3)] [P‐Pf3 = P(CH2CH2PPh2)3] (M = Cr, Mo) and Crystal Structures of the Latter Three
Authors: Horng Deng‐Nan , Jeng Shuenn‐Tay , Ueng Chuen‐Her 
Published: May 2015

AbstractThe triligate trimetallic complexes, [{M(CO)5}3(Pf‐Pf‐Pf)] and tetraligate tetrametallic complexes, [{M(CO)5}4(P‐Pf3)] (M = Cr and Mo), were prepared from [M(CO) 6] and the corresponding ligands in MeCN/CH2Cl2 promoted by Me3NO at 0 °C. Crystals of trimer lb are monoclinic, space group P 21/n, with a = 13.407(3), b = 15.002(5), c = 26.52(1) Å, β = 90.65(2)°, Z = 4, and R = 0.060 for 2760 observed reflections. Crystals of tetramer 2a are monoclinic, space group P 21/c, with a – 14.183(8), b = 29.880(4), c = 16.103(2) Å, β = 94.98(3)°, Z = 4, and R = 0.039 for 5014 observed reflections. Crystals of 2b are monoclinic, space group C 2/c, with a = 42.120(8), b = 13.679(1), c = 23.486(2) Å, β = 92.14(1)°, Z = 8, and R = 0.032 for 6897 observed reflections. Each phosphorus atom of the ligands is coordinated to the M(CO)5 moiety in each title compounds. The geometry of the four metals is a distorted tetrahedron for the tetramers.
Pyrazole Derivatives Part III Synthesis of Novel Naphtho[1,2‐c]pyrazolebenzenesulfonylureas, Thioureas and Their Cycllzed Derivatives
Authors: Faidallah Hassan M. , Makki Mohamad S. I. 
Published: May 2015

AbstractSubstituted p‐(naphtho[1,2‐c]pyrazol‐2‐yl)benzenesulfonylurea and thiourea derivatives 5–7 were prepared in three series. Cyclization of the thioureido group of compounds 7 by treating with ethyl bromoacetate, ethyl β‐bromopropionate and α‐bromoacetophenone afforded the corresponding thiazolidinone, thiazinone and thiazoline derivatives 8, 9 and 10 respectively.
Spatial Taming and Trapping of Molecules
Authors: Friedrich Bretislav , Herschbach Dudley 
Published: May 2015

AbstractMolecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field‐free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser‐induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer‐gas cooling, an intense infrared laser can typically confine molecules for long‐times (‐hours) within a small (‐picoliter) and cold (−1°K) “pocket of light.”
Picosecond Time Resolved Hard X‐Ray Diffraction from Laser Heated Metallic Crystals
Authors: Chen P. , Tomov I. V. , Rentzepis P. M. 
Published: May 2015

AbstractWe report the development of a novel hard X‐ray diffraction system with picosecond time resolution. Picosecond X‐ray pulses are produced by excitation of an X‐ray diode with picosecond ultraviolet light pulses at a repetition rate of 300 Hz. The X‐ray pulses are synchronized to the optical pulses with picosecond accuracy. The system has been utilized in picosecond time resolved X‐ray diffraction of laser pulse heated gold and platinum single crystals.
Duschinsky Effect in Sum Frequency Generation from Adsorbed Molecules
Authors: Vallet J. C. , Boeglin A. J. , Lavoine J. P. , Villaeys A. A. 
Published: May 2015

AbstractIt is the purpose of this work to give a theoretical description of the role played by the Duschinsky rotation in sum frequency generation experiments performed on adsorbed molecules. In addition to the mode mixing resulting from the Duschinsky rotation, frequency shifts as well as nuclear equilibrium position shifts, occuring under electronic excitation, are incorporated in the present model. The sum frequency generation spectra are calculated in order to compare the effects of the equilibrium position shifts and the quadratic mode mixing.
Modeling of Decay Rates for Molecules at an Island Surface
Authors: Xiong T. , Lcung P. T. , George Thomas F. 
Published: May 2015

AbstractThe decay rates for molecules at rough surfaces are studied via an island surface model, with particular emphasis on the effect due to the distribution of surface roughness. Two extreme cases are studied when the surface islands distribute themselves evenly and when they coalesce to form local clusters at the molecule‐substrate interface. The optical properties of the interfacial layer in these two cases are described by the Maxwell‐Garnett and the fractal‐cluster models, respectively. Among other results, it is found that both enhancement and suppression of the surface‐induced decay rates are possible due to the presence of roughness, with more dramatic suppression taking place when the surface islands coalesce to form clusters.
Chemical Constituents from the Roots of Neolitsea hiiranensis
Authors: Wu Shwu‐Li , Li Wen‐Shyong 
Published: May 2015

AbstractOne triterpenoid, taraxerone (1); four germacrane‐type sesquiterpene lactones, linderane (2), linderalactone (6), pseudoneolinderane (7), (+)‐linderadine (8); one sesquiterpene dilactone, pseudoneoliacine (10); three elemane‐type sesquiterpenes, isolinderalactone (3), compound 4 and sericealactone (9); one eudesmane type sesquiterpene, cryptomeridol (11); one glucoside, β‐sitosterol‐β‐D‐glucoside (12) along with β‐sitosterol (5) were isolated from the roots of Neolitsea hiiranensis. The structures of these compounds were identified on the basis of spectral properties.
Ring Enlargement of N‐Heterocycles
Authors: Liang Xiao‐Tian 
Published: May 2015

AbstractThis review describes our preliminary results of ring enlargement of N‐heterocycles by N‐ylide formation at a targeted site, exemplified by 55→56→58. Before development of this method, the strategy can be traced to our modified Hofmann degradation led at first to several miscarried probings on the reaction between N‐halomethyl ammonium salts and halophilic reagents.
Structural Tailoring of Monomolecular Films on Evaporated Silver Surface
Authors: Tao Yu‐Tai , Chang Shun‐Chi , Ma Li‐Fang 
Published: May 2015

AbstractMonomolecular films with well‐defined structure were prepared by self‐assembling of n‐alkanoic acids on an evaporated silver surface. Here we report the structural studies of thin films of acids containing aromatic chromophores of varied size and polarity. Information regarding the packing, orientation and conformation of the structural units within the assembly were deduced from ellipsometric thickness measurement, polarized reflection absorption infrared spectra and wetting property measurement. Implications of results to the design of functional thin films are discussed.
Convergent and Stereoselective Synthesis of Sarcophytol‐Q Precursor: (11S)‐3,7,11,15‐Tetramethyl‐11‐hydroxy‐14‐oxo‐3E,7E,12E‐hexadecatrienal
Authors: Li Wei‐Dong , Li Yu‐Lin , Li Ying 
Published: May 2015

AbstractA chiral precursor of sarcophytol‐Q, (11S)‐3,7,11,15‐tetramethyl‐11‐hydroxy‐14‐oxo‐3E,7E,12E‐hexadecatrienal, was synthesized in a convergent and stereoselective manner starting from geraniol and 4‐hydroxy‐2‐butanone in nine steps. The key steps were asymmetric Sharpless epoxidation, base‐induced dehydrohalogenation rearrangement of chiral epoxy chloride 5 and the phase transfer catalytic coupling reaction of allylic phenyl sulfone 4 with chiral allylic chloride 3.
Non‐Equivalent Hybrid Atomic Orbitals and Covalent Bonds in a2 Molecules
Authors: Chang Tse‐Chiang 
Published: May 2015

AbstractIn addition to having a noninteger value of λ for non‐equivalent hybrid atomic orbitals sp λ the introduction of a noninteger occupation number to a valence configuration for atoms in a molecule renders a precise account of the covalent bond in homonuclear diatomic molecules. For instance, the following bond orders 0.05, 1.42 and 2.62 are obtained for the molecules Be2, B2 and C2 according to the proposed method.
Potentiometric Determination of the Dissociation Constants of Glycylglycine in Various Aquo‐Organic Media
Authors: Azab H. A. , El‐Nady A. M. , Hamed M. M. A. , Ahmed I. T. 
Published: May 2015

AbstractThe dissociation constant values of glycylglycine were determined at 25 ± 0.1 °C (I = 0.1 mol L−1 KNO3) with Potentiometric pH titration in pure water and various mixture of water and organic solvents. The organic solvents used were methanol, ethanol, N, N‐dimethylformamide, dimethylsulfoxide, acetonitrile and dioxane. Initial estimates of the dissociation constants of glycylglycine were refined with ESAP2M computer program. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogeneity of the solvation shells around the solute.
Stereoselective Synthesis and Diels‐Alder Reactions of (Z)‐ and (E)‐1,2‐bis(Phenylthio)‐1,3‐Butadiene
Authors: Chou Shang‐Shing P. , Sun Der‐Jen , Hai‐Ping Tai  
Published: May 2015

AbstractBromination of 3‐phenylthio‐2‐sulfolene (2) with N‐bromosuccinimide gave 2‐bromo‐3‐phenylthio‐2‐sulfolene (3) which was converted mainly to 2,3‐bis(phenylthio)‐2‐sulfolene (4) by treatment with sodium phenylthiolate. Thermal desulfonylation of 4 at different temperatures in the presence of a base (DBU) yielded stereoselectively the (Z)‐ and (E)‐1,2‐bis(phenylthio)‐1,3‐butadiene (6). These two geometric isomers could be thermally interconverted. The Diels‐Alder reactions of 6 were also investigated. Only the (Z)‐diene 6a could undergo the Diels‐Alder reaction; the (E)‐diene 6b was in situ converted to the Z isomer before undergoing (he Diels‐Alder reaction. The reaction of 6a with N‐phenylmaleimide gave the cycloaddition product 7 with complete endo selectivity, but under daylight or during chromatography it readily underwent a thioallylic rearrangement to yield 8 with inversion of configuration. The cycloaddition of 6a with methyl acrylate proceeded regiospecifically, but generating a mixture of endo and exo isomers. The endo/exo ratio could be increased by using ZnCl2 as the catalyst.