Stereochemistry of allenic compounds : Absolute configuration of cycloallenols and cycloallenones

The absolute configuration of α-cycloallenols (3 and 4)as well as of α-cycloallenones(1)has been correlated to that of cyclic alkenols (2) by chemical transformations.     

Anthocyanidins and related compounds—VII Reactions of flavylium salts with 5,5-dimethyl-1,3-cyclohexanedione at pH 5·8

Phenolic flavylium salts, substituted and unsubstituted at position 3, condense with 5,5-dimethyl-1,3-cyclohexanedione in aqueous methanolic solutions at pH 5·8 to form novel cyclic flavan derivatives of types Xa and XIa.     

Mass spectra of organometallic compounds—VII; Organonitrogen derivatives of metal carbonyls

The positive-ion mass spectra of the following organonitrogen derivatives of metal carbonyls are discussed: (i) The compounds NC₅H₄CH₂Fe(CO)₂C₅H₅, NC₅H₄CH₂COMo(CO)₂C₅H₅, NC₅H₄CH₂W(CO)₃C₅H₅, NC₅H₄CH₂COMn(CO)₄, C₅H₁₀NCH₂CH₂Fe(CO)₂C₅H₅, (CH₃)₂NCH₂CH₂COFeCOC₅H₅ and (CH₃)₂NCH₂CH₂COMn(CO)₄ obtained from metal carbonyl anions and haloalkylamines, (ii) The isocyanate derivative C₅H₅Mo(CO)₃CH₂NCO; (iii) The arylazomolybdenum derivatives RN₂Mo(CO)₂C₅H₅ (R ? phenyl, p-tolyl, or p-anisyl); (iv) The compound (C₆H₅N)₂COFe₂(CO)₆ obtained from Fe₃(CO)₁₂ and phenyl isocyanate; (v) The N,N,N′,N′-tetramethylethylenediamine complex (CH₃)₂NCH₂CH₂N(CH₃)₂W(CO)₄. Further examples of eliminations of hydrogen, CO, and C₂H₂ fragments were noted. In addition evidence for the following more unusual processes was obtained: (i) Elimination of HCN fragments from the ions [NC₅H₄CH₂MC₅H₅]⁺ to give the ions [(C₅H₅)₂M]⁺ (M ? Fe, Mo and W); (ii) Conversion of C₅H₅Mo(CO)₃CH₂NCO to C₅H₅Mo(CO)₂CH₂NCO within the mass spectrometer; (iii) Elimination of N₂ from [RN₂MoC₅H₅]⁺ to give [RMoC₅H₅]⁺; (iv) Novel eliminations of HNCO, FeNCO, and C₆H₅NC fragments in the mass spectrum of (C₆H₅N)₂COFe₂(CO)₆; (v) Facile dehydrogenation of the N,N,N′,-N′-tetramethylethylenediamine ligand in the complex (CH₃)₂NCH₂CH₂N(CH₃)₂W(CO)₄.     

Absolute configuration of diastereomeric derivatives of N-substituted aziridine-2-carboxylic acids

Individual diastereomers of a number of anilides of N-substituted aziridine-2-carboxylic acids have been obtained. Conclusions regarding the spatial structure of the compounds indicated have been drawn on the basis of the ¹H NMR, ¹⁵N NMR, and CD spectra.Report 37 of the series entitled Asymmetric nonbridging nitrogen. For report 36 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1343–1348, October, 1984.     

Synthesis and Stereochemistry of Substituted 1,3-Dioxa-2-silacyclohexanes: VII. Synthesis and Stereochemistry of Substituted 2-Vinyl-2-methyl-1,3-dioxa-2-silacyclohexanes

The stereochemistry of substituted 2-vinyl-2-methyl-1,3-dioxa-2-silacyclohexanes was studied by ^1Hand ^13C NMR spectroscopy. The configurational and conformational assignment of a mixture of 2-vinyl-2,4-dimethyl-1,3-dioxa-2-silacyclohexane diastereomers with various ratios of the cis and trans forms was made. The molecules of both conformers occur chiefly in the chair conformartion with equatorial location of the methyl group at the C⁴ atom. The experimental data were confirmed by AM1 and MM+ optimization of the molecular geometry.     

Terpenoids—LX Absolute configuration of ar-turmerone

The absolute configuration of (+)ar-turmerone is shown to be II on the basis of the optical rotatory dispersion curve of the (+)hydrocarbon (VII) derived from it. The molecular rotations of the acid (III) and the alcohol (V) are in agreement with this conclusion.     

Fragmentation and rearrangement processes in the mass spectra of perhalogeno-aromatic compounds—VII. Pentafluorophenyl derivatives of nitrogen

The mass spectra of several perfluoroaromatic nitrogen compounds, including primary and secondary amines, diamines, nitriles, hydrazines, azines and azo compounds, are presented. Fragmentation patterns of these compounds are described and the data are discussed in terms of comparisons amongst perfluoroaromatic nitrogen compounds, and with reference to the hydrogen substituted analogs, or to oxygen and sulfur analogs of a particular compound.     

Cyclic organophosphorus compounds—II the infrared spectra of some 1,3,2-Dioxaphosphorinanes

The IR spectra of 47 1,3,2-dioxaphosphorinanes, mostly new compounds, have been recorded and discussed. Assignments have been made to P=O, P---O---C (alkyl and aryl), P=S and P---N stretching motions. In addition,it is suggested tentatively that multiple bands found at around 1000 to 1050 cm⁻¹ and at around 1150 to 1200 cm⁻¹ may be due to ring P---O---(C) vibrations.     

Mass spectrometry of hop compounds—III. Mass spectra of substituted 1,3-cyclopentanediones derived from hop constituents

The mass spectra of isohumulones (IV, V), tetrahydroisocohumulones (VI, VII), tetrahydroisohumulones (VIII) neohydroisocohumulones (XI, XII) cohumulinic acid (III), lupuloxinic acid (XV), humulinone (XIV) and related compounds are described. Ions which appear to be diagnostic for particular structures are discussed.     

Mass spectrometry of heterocyclic compounds—III. Electron-impact-induced fragmentation of 1,2-benzisothiazole and some 3-substituted derivatives

The mass spectra of fifteen 1,2-benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection. The parent compound of the series, 1,2-benzisothiazole, eliminates HCN after partial inter-ring hydrogen scrambling. The extent of scrambling has been determined for normal daughter ions produced at different electron beam energies and also for metastable daughter ions, and is compared with the data reported for benzothiazole. Some 3-substituted derivatives show unusual fragmentation patterns. The mechanisms of these processes are under further investigation.     

Mass spectrometry of onium compounds—XX: Ionisation potential in structural assignment of some gaseous molecules

The ionisation potentials for a series of thiazolo[3,2-a]pyridinium-3-oxides are reduced by about 1.7 to 1.8eV on introduction of an 8-OH group. The gaseous species from the former compounds are ascribed a mesoion, structure while the hydroxy-derivatives are rearranged to non charged molecules.     

Carbon-13 n.m.r. studies: 68—diastereomeric nonequivalence and the characterization of some bisnorbornylpinacols

The sodium-ammonia reduction of racemic norcamphor, exo-3-methylnorcamphor and 3,3-dimethyl-norcamphor (camphenilone) leads to substantial yields (60–90%) of the corresponding 2,2′-bisnorbornyl-2,2′-diols as diastereomeric mixtures. A combination of their ¹H, ¹³C and infrared spectra together with the results of periodic acid and lead tetraacetate oxidations permits stereochemical assignments for these six pinacols.     

Stereoselective Synthesis of 8,12-Furanoeudesmanes from Santonin. Absolute Stereochemistry of Natural Furanoeudesma-1,3-diene and Tubipofurane

Ketobutenolide 3, easily obtained from santonin (1), has been transformed into two natural furanoeudesmanes 4 and 5, isolated from Commiphora molmol and Tubipora musica, respectively. trans- And cis-decalin systems were obtained by stereoselective reduction of the C(4)-C(5) double bond in 3 in the following way: hydrogenation of 3 over Pd/C followed by acidic treatment gave the cis isomer 10 as the major product; selective hydrogenation of the C(1)-C(2) double bond with the Wilkinson's catalyst followed by reduction with NaTeH yielded mainly the trans isomer 9. Compounds 9 and 10 were transformed into 4 and 5 in parallel sequences. Optical rotation and CD measurements of the synthetic products revealed that the stereochemistry of both natural products should be revised to their enantiomeric form.     

Mass spectrometry of onium compounds—II. Carnitine and O-acyl derivatives

Carnitine and its O-acyl derivatives undergo two major pyrolytic reactions in the mass spectrometer. Firstly elimination of water from carnitine or acid from acylcarnitine takes place followed by intramolecular displacement and formation of crotonyl lactone and trimethylamine. Secondly intramolecular displacement occurs with formation of a substituted γ-lactone and trimethylamine. For the lower acid derivatives only the elimination pathway is important. For carnitine and higher derivatives both processes are important. The electron induced fragmentations of the major pyrolysis products are relatively simple. The most important pathways for the major components are discussed. The pyrolytic composition and mode of fragmentation are characteristic and can be used for identification purposes.     

Mesoionic compounds—XIX: Mass spectral fragmentation patterns for some five-membered systems containing oxygen,nitrogen and sulfur

Mesoionic compounds of the s-triazole, 1,3,4-oxadiazole, 1,3,4-thiadiazole, 1,2,3-thiadiazole, 1,3-thiazole and 1,3-dithiole systems all underwent deep-seated decomposition on electron-impact to small stable ions, determined to a large extent by the nature of the peripheral heteroatoms and the exocyclic substituent. In some instances fragmentation most probably involved an open-chain isomer of the cyclic system.     

Anthocyanidins and related compounds—VIII Condensation reactions of flavylium salts with 5,5-dimethyl-1,3-cyclohexanedione in acid solutions

4′-Hydroxyflavylium salts, unsubstituted at position 3, react with 5,5-dimethyl-1,3-cyclohexanedione in acid solutions to yield para-hydroxyphenacyl-5-keto-tetrahydroxanthene derivatives, e.g., Va, isomeric with the flavan derivatives, e.g., IIa, formed at pH 5·8. These flavans isomerize to the tetrahydroxanthenes in both acid and alkaline media.

7-Hydroxy- and 3-methyl-4′-hydroxyflavylium salts yield flavan derivatives, eq. IIIa, IId, when condensed either in acid solutions or at pH 5·8. Isomerization of these flavans to corresponding tetrahydroxyanthenes has not been detected.     

The NMR spectra and conformations of cyclic compounds—VII: The conformations of β-pinene,pinocarvone and the cis- and trans-pinocarveols

The proton magnetic resonance spectra of β-pinene pinocarvone and the cis- and trans-pinocarveols have been completely assigned at 220 and 300 MHz. On the basis of the proton-proton spin-spin couplings derived, conformations have been deduced for these molecules with greater certainty than has hitherto been possible. Pinocarvone is Y-shaped, while in all the other compounds the conformation is intermediate between a Y-shape and a bridged chair, with the C₃ atom bent away from the gem dimethyl groups. These conformations are discussed in terms of the steric interactions in these systems and are compared with related molecules.     

Chemistry of lichen constituents—VII: Mass spectra of some pulvic acid derivatives

The mass spectra of three methoxypulvic dilactones, four methyl esters of methoxypulvic acids and five methyl ethers of pulvic acid derivatives have been measured and rationalised employing accurate mass measurements and metastable peak assignments to substantiate the proposed fragmentations and rearrangements. In particular, the mass spectral differences and similarities between the isomeric methoxypulvic dilactones, between their methanolysis products and between the isomeric methyl ethers, are rationalised.