William H. Watson

The crystal structure of tris(acetylacetonato)(1,10-phenanthroline) europium(III)

Abstract The crystal structure of tris(acetylacetonato)(1,10-phenanthroline) europium(III), Eu(C 6 H 7 O 2 ) 3 (C 12 H 8 N 2 ), has been determined by single crystal X-ray diffraction techniques. A total of 4697 independent reflections were measured by counter methods and 2855 were considered to have an intensity significantly above background. The complex crystallizes in the monoclinic space group P2 1 c with four molecules per unit cell. The cell dimensions are a 0 = 9·670(8) A , b 0 = 21·339(5) A , c 0 = 16·497(5) A and β = 116° 11(10)′. The observed and calculated densities were found to be 1·37 g/cm −3 . The structure was refined by least-squares methods and a conventional R factor of 0·0334 was obtained for 1123 reflections. The calculated R for all 2855 observed reflections is 0·065. The molecules are monomeric and the europium ion is coordinated to eight ligand atoms which form a distorted square antiprism. Six EuO bond lengths average 2·397 A and two EuN bond lengths average 2·643 A. The distortion of the antiprism reduces the symmetry sufficiently for all characteristic electronic transitions to become allowed, and the full multiplicities are seen in the emission spectrum.

Glaucolide-A and -B, new germacranolide-type sesquiterpene lactones from Vernonia (compositae)

Abstract The structures of two new germacranolides, glaucolide-A ( 1a ) and -B ( 1b ), isolated from more than 25 species of Vernonia from the Western Hemisphere, have been established by a series of chemical transformations, and spectral and X-ray crystallographic studies.

Tetrachyrin, a new rearranged kaurenoid lactone, and diterpene acids from Tetrachyron orizabaensis and Helianthus debilis

Abstract (−)-Kaur-16-en-19-oic acid and tetrachyrin, a new rearranged kaurenoid lactone, were isolated from Tetrachyron orizabaensis var. websteri and Helianthus debilis ssp. debilis . The latter species also afforded angeloylgrandifloric acid.

The asymmetric reduction of ketones using chiral ammonium fluoride salts and silanes

Abstract Acetophenone and substituted arylalkyl ketones are reduced with moderate to good enantioselectivity by silanes bearing alkoxyl or siloxy groups and chiral ammonium fluoride salts derived from cinchona alkaloids.

β-Isocomen, ein neues sesquiterpen aus Berkheya-arten

Abstract The investigation of several Berkheya species afforded in addition to already known compounds three unusual sesquiterpene hydrocarbons. Together with modhephene and isocomene, a new one is present, its structure being elucidated by spectroscopic methods and by some chemical transformations. All 18 species investigated contain the typical thiophene derivatives, isolated earlier; the patterns of compounds present divide the species into two groups.

Terpenoids and flavonoids from the aerial parts of Salvia candidissima

From the aerial parts of Salvia candidissima, a new diterpene, 3-oxosalvipisone, was obtained together with 11β-hydroxymanoyl oxide, 8,13-diepimanoyl oxide, spathulenol, salvigenin, crysoeriol, diosmetin and o,p-dimethoxybenzoic acid. The structure of the new compound, 3-oxosalvipisone was established by spectroscopic means, and the structure of 11β-hydroxymanoyl oxide was reinvestigated by extensive 1D and 2D NMR studies and confirmed by X-ray analysis.

Tetrathiafulvalene quinones, hydroquinones and esters

Abstract Benzocyclohexa-2,5-diene-1,4-dione-1,3-thiole-2-thione (2) was synthesized starting with 2,3-dichloronapthoquinone (1). Compounds 3 and 4 were also obtained; however, the yield of 2 can be increased through control of the temperature and reaction time. Reaction of 2 with triethylphosphite gave 5 and the tetrathiafulvalene ester 6. The tetrathiafulvalenequinone (9) was obtained by hydrolysis of 6 followed by oxidation of 8. Compound 9 was obtained more directly by hydrogenation of 2 followed by coupling with triethylphosphite and oxidation. Chloranil was used to prepare the dithiafulvene quinone 12 which was reduced, coupled with triethylphosphite to form, presumably , polymer 13. The reactions were repeated using the hexanoic acid esters of the corresponding hydroquinone thiafulvalenes. The crystal structures of 2, 3, 4, 5, 6a and 10 were determined by X-ray diffraction. Cyclic voltammetry studies show the tetrathiafulvalene quinones reduce like quinones, but do not exhibit the oxidation properties of tetrathiafulvalenes.

1,1′-Bis(diphenylphosphino)ferrocene ligand substitution in the benzylidyne-capped cluster PhCCo3(CO)9. Synthesis, X-ray structure, and redox reactivity of PhCCo3(CO)7(dppf)

Abstract The reaction between 1,1′-bis(diphenylphosphino)ferrocene (dppf) and the tricobalt cluster PhCCo 3 (CO) 9 ( 1 ) yields the disubstituted cluster PhCCo 3 (CO) 7 (dppf) ( 2 ). The dppf ligand in 2 bridges adjacent cobalt centers via axial coordination. Ligand substitution leading to 2 may be achieved by thermolysis, oxidative decarbonylation using trimethylamine oxide, and by electrontransfer chain (ETC) catalysis using sodium benzophenone ketyl. The isolated yield of 2 ranged from 50 to 70% in all cases. Solution characterization of 2 by FT-IR and 31 P NMR spectroscopy is presented along with the single-crystal X-ray diffraction results. The dppf-bridged cluster PhCCo 3 (CO) 7 (dppf)·(toluene) crystallized in the monoclinic space group P 2 1 / c with a = 13.560(3), b = 17.339(3), c = 21.482(3) A, β = 106.81(1)°, V = 4835(1) A 3 and Z = 4. Block-cascade least-squares refinement yielded R = 0.0630 for 5055 ( I > 3σ( I )) reflections. The redox reactivity of 2 was examined by cyclic voltammetry, which revealed the presence of two irreversible oxidations that are attributed to the oxidation of the dppf ligand and the cluster core along with the observation of an irreversible reduction that exhibits cyclic voltammetric curve crossing. All of the redox processes are discussed with respect to existing tricobalt cluster redox chemistry.

Intramolecular alkene-oxirane cycloadditions. Synthesis and structure of 5-oxapentacyclo [7.3.0.03,7.o4,12.06,10]dodecane-2,8-dione

Abstract MCPBA promoted epoxidation of the C(9)-C(10) double bond in endo -tricyclo [6.2.1.0 2,7 ]undeca-4, 9-diene-3,6-dione ( 4 ) followed by intramolecular [2 + 2] photocyclization of the resulting exo epoxide ( 5 ) afforded the title compound, 1 , in 16% overall yield. The structure of symmetrically hydrated 1 (i.e., 1a ) was determined by single crystal X-ray crystallographic methods. Proton and carbon-13 NMR spectral assignments are given for epoxide 5 .

Synthesis and Alkali Metal Picrate Extraction Capabilities of Novel, Cage-Functionalized, Pyridine Containing Crown Ethers and Cryptands

Abstract The syntheses of novel cage-functionalized crown ethers,11–13, that contain one or more pyridyl units are reported. The results of alkali metal picrate extraction experiments performed by using11 and12 are compared with those obtained by using the corresponding model (non-cage) crown ethers. Cage-functionalized crown ether11 displays greater avidity toward Li+ picratevis-a`-vis the corresponding model system,2, whereas12 displays considerably lower avidity than its corresponding model system,3, toward extraction of alkali metal picrates from aqueous solution into CHCl3. In addition, a highly preorganized, cage-annulated cryptand,16, was prepared; this unusual host molecule was found to be both highly avid highly selective toward extraction of Li+ and Na+ picrates. Download : Download full-size image