Stereoselective syntheses of substituted methyl (Z,E,E)-deca-2,7.9-trienoates and substituted methyl (Z,E,E)-undeca-2,8,10-trienoates

Lindlar hydrogenation of substituted methyl ($\text{E}$,$\text{E}$)-deca-7,9-dien-2-ynoates and substituted methyl ($\text{E}$,$\text{E}$)-undeca-8,10-dien-2-ynoates affords selectively the corresponding ($\text{Z}$,$\text{E}$,$\text{E}$)-trienes.     

Stereoselective Synthesis of（E）—and（Z）—1,2—Disubstituted Ethene from Polymer—Supported vinylic Selenide

This letter describes a method for the stereoselective synthesis of polymer-supported vinylic selenides and their applications to synthesis of(E)-and(Z)-1,2-disubstituted ethenes on solid-phase by the couplig reaction with Grignard reagents under the catalysis of NiCL2(PPh3)2.     

Differentiation of diastereomeric conduramine derivatives under electron ionization and chemical ionization mass spectral conditions

Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.     

The sensitized photooxygenation of methyl substituted 1,2-diphenylcyclobutenes

A series of Me substituted 1,2-diphenylcyclobutenes was subjected to dye-sensitized photooxidanon in the presence ofmethylene blue. In the case of the 3,3-dimcthyl-, 3,3,4-tnmethyl- and 3,3,4,4tetramcthyl, 2-diphcnylcyclobutencs, the sensitized oxidations arc accompanied by ring-contraction with concomitant ortho hydroxylation of one aromatic nucleus. When electron transfer induced photooxidation techniques utilizing 9,10-dicyanoanthraccne (DCA) as a sensitizer are employed with the series of Me substituted diphcnykyclobutenes, the reactions take a markedly different course and a broad spectrum of oxidation products are obtained including, most notably, ozonides of the cyclobutencs. The mechanisms of these conversions are addressed and the significance of the results discussed.     

Candidate Trail Attractants of Reticultermes lucifugus: Stereoselective Syntheses of (3Z, 6E,BE)-(3Z, 6E, 8Z)-and (3Z, 6Z, 8Z)-3,6,8 -Dodecatrien-1-OL1

Stereoselective syntheses on a gram scale of (3Z,6E,8E)-, (3Z,6E,8Z)-and (3Z,6Z,8Z)-3,6,8-dodecatrien-1-ol, 8, 9 and 10, respectively, are described. A key step of the synthesis of 8 consisted of a copper-mediated coupling reaction between 4-(2-tetrahydropyranyloxy)-1-butynylmagnesium bromide (15) and the mesyl ester of (2E,4E)-2,4-octadien-1-ol (14). A similar copper-mediated reaction between 15 and the mesyl ester of (E)-2-octen-4-yn-1-ol (19) was used to construct the C-12 carbon skeleton of 9. On the other hand, the synthesis of 10 was based on a palladium-promoted reaction between (Z)-1-bromo-1-pentene (23) and the organozinc bromide derived from 3,6-heptadiyn-1-yl acetate (27).     

Mass spectral fragmentation of bis(1-arylimino-1-alkyl/arylthiomethyl) disulfides under positive electrospray ionization conditions

The mass spectral fragmentation of bis(1-arylimino-1-alkyl/arylthiomethyl) disulfides under positive electrospray ionization conditions has been investigated. The protonated molecular ions predominantly produce trisulfide thiocarbonimidate ions by elimination of a molecule of arylisonitriles. The trisulfide thiocarbonimidate ions further lose a sulfur atom to yield disulfide thiocarbonimidate ions and then eliminate a molecule of thiols or disulfanes to give rise to the corresponding dithioisonitriliums or thioisonitriliums, respectively. Both alkyl dithio and thioisonitriliums can undergo a McLafferty-type rearrangement to yield the corresponding protonated arylisothiocyanoates. The major characteristic of bis(1-arylimino-1-alkyl/arylthiomethyl) disulfides is loss of diverse neutral molecules, such as isonitriles, thiols, thioaldehydes, and disulfanes under positive electrospray ionization conditions.     

An ab Initio study of conformational properties of (Z,Z)-, (E,Z)- and (E,E)-cycloocta-1,5-diene

Ab initio calculations at HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the three geometrical isomers of cycloocta-l,5-diene 1–3.     

Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization

The 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring-chain tautomerism was obtained under these conditions. Analogously to other related five-membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH₃CO]⁺ adduct ions. These adducts were stable, however, and unlike those of 1,3-dioxolanes and 1,3-oxathiolanes, they did not decompose and form stable oxonium ions.     

Mass spectrometric behaviour of 1-imino-substituted pyrazolo[1,2-a]-[1,2,4]triazoles under electron and chemical ionization

The spectra of five pharmacologically interesting substituted pyrazolo[1,2-a][1,2,4]triazole hydroiodides were measured under electron and chemical ionization. In the electron ionization spectra, in addition to the intense molecular ion peak of the free base (M⁺*), there was also a relatively intense molecular ion peak of the hydroiodide form, which is unusual since the hydroiodides are rarely so stable. The phenylimino and phenylamino substituents of the triazole ring affected the fragmentation behaviour of the compounds very much. The chemical ionization reagent gases used in this work were methane, isobutane, deuterated ammonia and acetone. In all the cases practically only [M+H]⁺ ions were observed, the only exception being acetone which also gave rise to intense [M+C₂H₃O]⁺ and [M⁺C₃H₇O]⁺ adduct ions. None of the reagent gases used was able to cause any fragmentation.     

Mass spectral study of meso-alkyl and meso-cycloalkyl calix(4)pyrroles under electron impact conditions

A series of meso-cycloalkyl calix(4)pyrroles (I) and meso-dialkyl calix(4)pyrroles (II) has been studied under electron ionization (EI) mass spectral conditions. All the calix(4)pyrroles showed prominent molecular ions. The cleavage of the C--C bond linked at position 2 of the pyrrole ring (beta-cleavage) is the foremost and dominant fragmentation process. The beta-cleavage process, either through ring opening or directly, results in the loss of an alkyl radical from the molecular ion. The collision-induced dissociation (CID) spectra of I showed specific sequential expulsion of pyrrole and/or cycloalkyl rings from the molecular ion with or without hydrogen migrations, revealing more information on the structure of individual compounds than was available from the EI spectra. The isomeric cycloalkyl calix(4)pyrroles showed distinguishable CID spectra, indicating structure specificity in initial ring opening whereas, in the case of II, the EI mass spectrum contains all the structure-indicative fragment ions. The CID spectra of II resulted in a dominant [M-R]+ ion, with other characteristic ions being less abundant.