I.M. Kolthoff,P.J. Elving and F.H. Stross (Editors), Treatise on analytical chemistry. Part III. Analytical chemistry in industry : Vol. 2, Wiley-Interscience,New York, 1971, xxiv+597 pp., price £ 12.00

The titration of some substituted azoles in non-aqueous solution has been studied and their relative basic strengths determined. Differentiating titration of mixtures of substituted imidazoles is only possible when one of the imidazoles is substituted with a powerful electronegative substituent, e.g. a nitro group. Azolium halides may be titrated with perchloric acid in anhydrous acetic acid after addition of mercury(II) acetate, or dissolved in acetic anhydride without addition of mercury(II) acetate; dissolved in methanol, they may be titrated as acids with tetrabutylammonium hydroxide in benzene/methanol. The acidic and basic properties of some substituted pyrazol-5-ones have been compared.     

Stericaliy Congested Molecules: 2,2′-[(Biaryldiyl)bis(oxy)]bis[1,3,2-oxazaphospholidines]

The original suggestion that a through-space mechanism was operative in the seven-bond J(P, P) coupling constant of 30.3 Hz observed for 3.3′-bis(1,1-dimethylethyl)-2,2′-[3,3′,5,5′-tetrakis(1,1-dimethylethyl)-1,1′-biphenyl-2,2′-diyl]bis(oxy)}bis[1,3,2-oxazaphospholidine] ( 1a )) was investigated. In the solid-state CP-MAS ³¹PNMR spectrum of 1a , two nonequivalent P -atoms were observed; sufficient resolution could not be obtained to determine whether P, P coupling was present. The preparation and spectral data of the N-methyl analogue 1b and of the acyclic N-isopropyl analogue 6 (Scheme 1) provided evidence that a) the essentially exclusive formation (R*, R*,S*)- 1a in the reaction of the disodium biphenyldiolate 3a with the phosphorochloridite 4a is the result of significant differences in the free energy of activation (ΔG*) for the formation of the various diastereoisomers due to the steric congestion within the molecule and that b) the magnitude of the observed P,P coupling is dependent upon the degree of conformational freedom within the molecule. In the ³¹P-NMR spectrum of the P-sulfide 7 , which was prepared by the reaction of la with sulfur, 2s resonances were observed that strongly suggested that the lone electrons pair on P are involved in the mechanism for the transmission of coupling data. The (4S,5R) -12 and (4R, 5S) -12 of la were prepared in a three-step reaction sequence starting from the corresponding enantiomerically pure norephredine 8 (Scheme 2). Both (4S, 5R)- and (4R, 5S) -12 were obtained as a diastereoisomer mixture that differ by the configuration of the axis of chirality, i.e., (R*R*,R*)- and (R*,S*,R*) -12 were obtained. The major diastereoisomer was obtained upon recrystallization, and the atropisomers were observed to equilibrate in solution by monitoring the H? C(5) resonance in the ¹H-NMR with time (ΔG° = 0.4 kcal/mol; Fig. 2). The process observed corresponds to the restricted rotation about the central single bond of the biphenyl system. The isolation of an atropisomer with only a single ortho substituent on each aryl ring is quite rare. In the ¹³C-NMR spectrum of both (R*,R*,R*)- and (R*,S*,R*) -12 , C(5) is two-bond-coupled to the oxazaphospholidine P-atom (²J(C(5),P((2)) = 8.5 Hz) that is further virtually coupled to the P-atom of the other oxazaphospholidine ring (7J(P(2),P(2′)) = 30 Hz; ⁹J(C(5),P(2′)) = 0 Hz; δ(P(2)) = δ(P(2′)) = 136 ppm. In the ³¹P-NMR spectrum of (R*,R*,S*) -12 , which was prepared from the racemic chloridite (mixture of three diastereoisomers was obtained), a ⁷J(P(2),P(2′) of 36 Hz was observed. These observations provide strong evidence that seven-bond P,P coupling occurs in all three diastereoisomers of 12 . The observed P,P coupling is both independent of the configuration of the chiral axis and the configuration of the asymmetric P-centers. This independence of P,P coupling upon the configuration on P implies also the independence of the observed coupling upon the orientation of the lone-pair of electrons on P provided that the conformations of the diastereoisomers are similar in solution. The X-ray crystal structure of the complex formed from 1a and dichloro(cycloocta-1,5-diene)platinum(II) was obtained and the solid-state structure discussed. The major diastereoisomer of (4S,5R) -12 was used as a chiral ligand in asymmetric hydrosilylation and hydrogenation reactions (Scheme 3).     

Synthesis of an Azasteroid Using an Acyl Iminium Ion-Initiated Tandem Cyclization

An acyl iminium ion-initiated tandem cyclization gave an unexpected dienone product, a seco-azasteroid (2). The factors governing the formation of 2 were investigated in an attempt to optimize its formation. The reaction was applied to a more elaborate system, resulting in the synthesis of the full steroid skeleton of 13-azaandrosta-1,4-diene-3,17-dione (3), which contains the unusual substitution of a chlorine atom for the axial 19-methyl.     

Chemistry of (η5-C5H5)Ru(Ph2PCH2CH2PPh2)Cl: preparation of cationic ruthenium olefin complexes

The cationic ruthenium complexes [(η⁵-C₅H₅)Ru(Ph₂PCH₂CH₂PPh₂)L]PF₆ (L=olefin, CO, pyridine or acetonitrile) have been prepared by treatment of (η⁵-C₅H₅)Ru(Ph₂PCH₂CH₂PPh₂)Cl with L and NH₄PF₆ in methanol of 20°C.     

Enantioselective syntheses of tremulenediol A and tremulenolide A

[reaction: see text] An enantioselective entry to the skeleton of the tremulane sesquiterpenes is described. The approach features a series of efficient transition metal-catalyzed reactions commencing with an enantioselective rhodium(II)-catalyzed intramolecular cyclopropanation followed by a regioselective allylic alkylation and a diastereoselective rhodium(I)-catalyzed [5 + 2] cycloaddition. This strategy was applied to the first enantioselective syntheses of tremulenediol A and tremulenolide A.     

Maximal subgroups of the orthogonal group

Let V be an n-dimensional regular quadratic space over a field K of characteristic not 2. Assume n 4. Let W be a regular hyperplane and v a nonzero vector orthogonal to W. Suppose every regular hyperplane in W is universal. If is an isometry of V not leaving W invariant, then , together with the isometries of W, generate the orthogonal group of V, with one exception.The work of the author was partially supported by NSERC Grant A-7862.     

Zur Kenntnis der RbNiCrF6Typs. III. Neue Fluoride des Typs CsZnMF6 mit M = Al,Ga, In,Tl, Sc,Ti, V,Mn, Cu,Rh

On the RbNiCrF₆ Type. III. New Fluorides of the Type CsZnMF₆ (M = Al, Ga, In, Tl, Sc, Ti, V, Mn, Cu, Rh) Cubic compounds are CsZnGaF₆ [3] (colourless, a = 10.29 Å); CsZnInF₆ (colourless, a = 10.58 Å); CsZnTlF₆ (colourless, a = 10.62 Å); CsZnScF₆ (colourless, a = 10.58 Å); CsZnTiF₆ (lightblue, a = 10.50 Å); CsZnVF₆ (lightgreen, a = 10.43 Å); CsZnMnF₆ (redbrown, a = 10.40 Å); CsZnCuF₆ (light brown, a = 10.24 Å); CsZnRhF₆ (redbrown, a = 10.41 Å), all RbNiCrF₆ type of structure, in addition non cubic: CsZnAlF₆ (colourless). The Madelung part of lattice energy, MAPLE, is calculated and discussed.     

Intra- and intermolecular complexation in C6 monoazacoronand substituted cyclodextrins

The preparation of 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)acetamido)hexylamino)-alpha-cyclodextrin, 3, 6(A)-deoxy-6(A)-(6-(2-(1,4,7,10,13-pentaoxa-16-azacyclooctadecan-16-yl)acetamido)hexylamino)-alpha-cyclodextrin, 4, and their beta-cyclodextrin analogues, 5 and 6, are described. (1)H (600 MHz) ROESY NMR spectra of the C(6) substituted beta-cyclodextrins, 5 and 6, are consistent with the intramolecular complexation of their azacyclopentadecanyl- and azacyclooctadecanyl(acetamido)hexylamino substituents in the beta-cyclodextrin annulus in D(2)O at pD = 8.5 whereas those of their alpha-cyclodextrin analogues, 3 and 4 are not complexed in the alpha-cyclodextrin annulus. This is attributed to the monoazacoronand components of the substituents being able to pass through the beta-cyclodextrin annulus whereas they are too large to pass through the alpha-cyclodextrin annulus. However, the substituents of 3 and 4 are intermolecularly complexed by beta-cyclodextrin to form pseudo [2]-rotaxanes. Metallocyclodextrins are formed by 5 through complexation by the monoazacoronand substituent component for which log (K/dm(3) mol(-1))= <2, 6.34 and 5.38 for Ca(2+), Zn(2+) and La(3+), respectively, in aqueous solution at 298.2 K and I= 0.10 mol dm(-3)(NEt(4)ClO(4)).     

Catalysts for Suzuki-Miyaura coupling processes: scope and studies of the effect of ligand structure

Suzuki-Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl- and vinylboronic acids proceed in very good to excellent yield with the use of 2-(2',6'-dimethoxybiphenyl)dicyclohexylphosphine, SPhos (1). This ligand confers unprecedented activity for these processes, allowing reactions to be performed at low catalyst levels, to prepare extremely hindered biaryls and to be carried out, in general, for reactions of aryl chlorides at room temperature. Additionally, structural studies of various 1.Pd complexes are presented along with computational data that help elucidate the efficacy that 1 imparts on Suzuki-Miyaura coupling processes. Moreover, a comparison of the reactions with 1 and with 2-(2',4',6'-triisopropylbiphenyl)diphenylphosphine (2) is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an interesting C-H bond functionalization-cross-coupling sequence intervenes to provide product in high yield.     

A Comparative Study on Analysis of Ginsenosides in American Ginseng Root Residue by HPLC-DAD-ESI-MS and UPLC-HRMS-MS/MS

Ginseng (Panax quinquefolius), a popular herbal and nutritional supplement consumed worldwide, has been demonstrated to possess vital biological activities, which can be attributed to the presence of ginsenosides. However, the presence of ginsenosides in ginseng root residue, a by-product obtained during processing of ginseng beverage, remains unexplored. The objectives of this study were to develop a high-performance liquid chromatography-photodiode array detection-mass spectrometry (HPLC-DAD-ESI-MS) and an ultra-high-performance-liquid-chromatography-tandem mass spectrometry (UPLC-HRMS-MS/MS) method for the comparison of ginsenoside analysis in ginseng root residue. Results showed that by employing a Supelco Ascentis Express C18 column (150 × 4.6 mm ID, particle size 2.7 μm) and a gradient mobile phase of deionized water and acetonitrile with a flow rate at 1 mL/min and detection at 205 nm, a total of 10 ginsenosides, including internal standard saikosaponin A, were separated within 18 min and detected by HPLC-DAD-ESI-MS. Whereas with UPLC-HRMS-MS/MS, all the 10 ginsenosides were separated within six minutes by using an Acquity UPLC BEH C18 column (50 × 2.1 mm ID, particle size 1.7 μm, 130 Å) and a gradient mobile phase of ammonium acetate and acetonitrile with column temperature at 50 °C, flow rate at 0.4 mL/min and detection by selected reaction monitoring (SRM) mode. High accuracy and precision was shown, with limit of quantitation (LOQ) ranging from 0.2–1.9 μg/g for HPLC-DAD-ESI-MS and 0.269–6.640 ng/g for UPLC-HRMS-MS/MS. The contents of nine ginsenosides in the ginseng root residue ranged from <LOQ-26.39 mg/g by HPLC-DAD-ESI-MS and <LOQ-21.25 mg/g by UPLC-HRMS-MS/MS, with a total amount of 38.37 and 34.71 mg/g, respectively.