Conjugated Diene System Research Articles

Potential involvement of free radical reactions in ultraviolet light-mediated cutaneous damage.

AbstractFree radicals are chemical species characterized by an odd number of orbital electrons or by pairs of electrons of similar directional spin isolated singly in separate orbitals. Consequently most of these agents are highly reactive and usually exhibit an extremely short half‐life, although due to steric and resonance effects some exceptions occur. Some radicals and their precursors, such as the diradical O2 which exists in the triplet state, represent a critical and essential element of normal metabolism of aerobic organisms where, under normal circumstances, controlled reduction of reactive oxygen species occurs via the cytochrome oxidase or cytochrome P‐450 mixed function monooxygenase systems. In addition to reactive oxygen species, organisms may be subjected to a wide‐range of other free radicals or their precursors, including those of both exogenous and endogenous origin. Elaborate defense mechanisms have evolved to avoid cellular damage from these highly reactive species. Enzymes, such as the superoxide dismutase, the glutathione peroxidase/reductase system, and catalase; interactions with conjugated diene systems such as those found in melanins, carotenoids, and tocopherols; and direct reduction by sulphydryl compounds, phenols, and purines represent but a few of these natural defense systems.Despite a strong rationale for considering free radicals as pathologic agents, progress in implicating these agents, or their reactions, in pathologic processes has been arduous. The fore‐most hurdle to providing definitive evidence for free radical involvement rests with the highly transient nature of these species, hardly reaching measurable levels in vivo and thereby making rigorous testing of the hypothesis extremely difficult. Indeed, free radical damage has been studied, for the most part, by indirect means–usually by measurement of known free radical reaction intermediates and products from which free radical involvement is implied. Nevertheless, free radical formation has been shown to occur in UV‐irradiated skin and a considerable body of circumstantial evidence has been amassed that strongly infers that these agents, or reactions initiated by them, are responsible for at least some of the deleterious effects of UV upon skin.

ChemInform Abstract: Novel Formation of Bis‐Allylic Products by Autoxidation of Substituted Cyclohexa‐1,4‐dienes.

AbstractIn contrast to acyclic homoallylic dienes, which are autoxidized to conjugated diene systems, the cyclic analogue (Ia), which is stable indefinitely under nitrogen, on standing neat in air undergoes clean conversion to a mixture of the keto ester (III) and methyl benzoate (IV).

Lepidopterous sex attractants with a conjugated diene system.

Each of fifty-one conjugated dienes (alcohols, acetates and aldehydes) with a C12, C14 or C16 straight chain was applied to a rubber cap in a sticky-type trap as a single-component lure. Some diene compounds were mixed with their functional derivatives or structurally related monoenes to make two-component lures. In field trials conducted from 1984 to 1986, the new attraction of male moths of nineteen species was observed. These species were classified into nine families as follow: Gracillariidae, Yponomeutidae, Oecophoridae, Cosmopterigidae, Tortricidae (Olethreuti- nae and Tortricinae), Pyralidae, Pterophoridae, Drepanidae and Geometridae. This result indicates that the conjugated dienes are one of the main groups of lepidopterous sex pheromones. Some interesting information concerned with the taxonomy of the attracted moths and with the characteristics of the chemical structures of their attractants was obtained.

ChemInform Abstract: Stereoselective Formation of cis‐2,3‐Dimethylcyclopropanone Hemiacetals from 2‐Halo‐3‐pentanones. [4 + 3]Cycloadditions with Conjugated Diene Systems.

AbstractThe halopentanones (Ia) or (Ib) react in the alcohols (II) with the corresponding alkoxides in a highly stereoselective manner to give the hemiacetals (IIIa)‐(IIIc) [X‐ray 28 analysis of the derivative (IIId) from (IIIa): P21/c; Z = 8].

Mass spectra of deuterated sex pheromones with a conjugated diene system.

Mass spectra of deuterated sex pheromones with a conjugated diene system.

Photosensitized oxidation of methyl linolenate monohydroperoxides: Hydroperoxy cyclic peroxides, dihydroperoxides and hydroperoxy bis‐cyclic peroxides

AbstractTo elucidate the biological and flavor significance of lipid secondary oxidation products, cyclic peroxides were prepared by photosensitized oxidation of the hydroperoxides in autoxidized methyl linolenate. The oxidation product was fractionated by silicic acid chromatography, followed by high pressure liquid chromatography (HPLC) on a microporous silica column. Products characterized by thin layer chromatography (TLC), gas chromatography (GC), ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR) and mass spectroscopy (MS) included 6‐membered cyclic peroxides (9‐hydroperoxy‐10,13‐epidioxy‐11, 15‐and 16‐hydroperoxy‐12,15‐epidioxy‐9, 13‐octadecadienoates), 15‐membered cyclic peroxides (9‐hydroperoxy‐10,12‐epidioxy‐13,15‐ and 16‐hydroperoxy‐13, 5‐epidioxy‐9,11‐octadecadienoates), dihydroperoxides (9,12‐; 9,16‐; 10,12‐; 10,15‐; 10,16‐; 13,15‐; 13,16‐dihydroperoxy octadecatrienoates) and hydroperoxy bis‐cyclic peroxides, each with one 5‐and one 6‐membered ring (9‐hydroperoxy‐10,12,13,16‐bis‐epidioxy‐14‐ and 16‐hydroperoxy‐9,12,13, 15‐bis‐epidioxy‐10‐octadecenoates). The 6‐membered cyclic peroxides are formed by 1,4‐addition of singlet oxygen to the conjugated diene system in 9‐ and 16‐linolenate hydroperoxide isomers after their isomerization to thetrans, trans configuration. The bis‐cyclic peroxides are formed by 1,4‐addition of singlet oxygen to the hydroperoxy 5‐membered cyclic peroxides derived from the 12‐ and 13‐linolenate hydroperoxide isomers. Secondary oxidation products similar to those identified in this study previously have been shown to be important precursors of volatile compounds that may contribute to flavor deterioration of fat‐containing foods.

ChemInform Abstract: UNSATURATED SUGARS: AN ALTERNATIVE ROUTE TO 3,5,6‐TRIDEOXY‐1,2‐O‐ISOPROPYLIDENE‐α‐D‐GLYCERO‐HEX‐3,5‐DIENOFURANOSE

AbstractDie Glukofuranose (I) kann mit dem System Azodicarbonester (II), Triphenylphophin schonend zum Oxiran (III) dehydratisiert werden.

Transition metal catalyzed reactions of diazoesters : Cyclopropanation of dienes and trienes

The regioselectivity of the cyclopropanation of polyenes by cycloaddition of carbenes generated by catalyzed decomposition of diazoesters in the presence of Rh, Pd and Cu catalysts can be controlled to some extent by selecting proper reaction parameters. For a particular diene, the regioselectivity depends both on the catalyst and on the nature of the double-bond (conjugation, substitution). The cyclopropanation of trienes containing both a conjugated diene system and an isolated double bond is reported as an application of these reactions. The practical interest of the present study is further demonstrated by the synthesis of a pyrethroid precursor by the rhodium(II) carboxylates catalyzed-cyclopropanations of 1.1-dichloro-4-methyl-1, 3-pentadiene.

13C NMR analyses on conjugated dienic pheromones of lepidoptera.

13C NMR spectra of all the geometrical isomers of 5,7- and 8,10-dodecadien-1-ols and 9,11-dodecadienyl acetate were studied, and a new method for assigning 13C signals of a conjugated system is proposed. The method is based on two empirical rules. The first involves the 13C shift differences of olefinic carbons induced by a substitutional change at an end of the conjugated diene system, namely the change from a methylene to a methyl at Cf in the Ca-Cb = Cc-Cd = Ce-Cf diene system. The second rule concerns the chemical shift changes of allylic and olefinic carbons by converting the geometry of conjugated diene systems. Namely, when the (E)-configuration of a Cb = Cc double bond in the diene system is changed into a (Z)-configuration without the conversion of the Cd = Ce double bond, the signals of Ca, Cb, Cc and Cd shift upfield by 5.1 ± 0.3, 2.6 ± 0.3, 1.9 ± 0.3 and 4.9 ± 0.2 ppm, respectively, and the signal of Ce downfield by 2.2 ± 0.2 ppm, regardless of the geometry of the Cd = Ce double bond.

Elimination reaction of angular hydroxymethyl groups of 20(29)-lupene derivatives

Solvolysis of 28-p-toluenesulfonyloxy-20(29)-lupene derivatives IV-VII proceeds with isomerization of the isopropenyl side chain to the isopropylidene chain and expansion of the ring E to a six-membered ring, containing trisubstituted double bond; for „anhydrobetulin" and its derivatives formulae VIII-XI with homoconjugated double bonds are suggested. Formation of a conjugated diene system is hindered by steric interactions of the isopropylidene chain with the ring C (with C(12)). Only the trisubstituted double bond in the dienes VIII and X undergoes catalytic reduction, the hydrogen approaching from the α-side (XII-XVI) as demonstrated by the Cotton effect of trinorketone XXI and its 20,20-dibromo derivative XXIII.

Catalytic hydrocyanation of dienes and trienes

The hydrocyanation of dienes and trienes using nickel-(0)-phosphite complexes as catalysts yielded various mono- and dinitriles, which can be important starting materials in organic syntheses. The reactivities of conjugated and isolated dienes were compared and the products formed could be explained by either an alkyl or an allyl mechanism. The hydrocyanation of conjugated dienes yielded mainly 1,4-adducts. The conversion of the diene decreased in the series butadiene > piperylene > isoprene indicative for the formation of η 3-allyl systems, which show different stability. The hydrocyanations of nonconjugated α-ω-diolefins, such as 1,4-pentadiene, 1,5-hexadiene, and 1,7-octadiene, yielded various nitriles depending on the number of methylene groups separating the two double bonds. Whereas 1,4-pentadiene and 1,5-hexadiene yielded mainly products originating from conjugated dienes formed by isomerization, 1,7-octadiene gave sebacic dinitrile in a yield of 22%. 1,3,7-Octatriene, which contains an isolated double bond and a conjugated diene system combined in one molecule, gave six nitriles in which the cyano groups are attached to carbon number 2 or 4 of the C 8 chain. The products can be explained by an allyl mechanism and concomitant isomerization.

Corrected structure of the reaction product of gibberellin A3 with acetic anhydride and zinc and its crystalline structure. Rare case of the diels-alder reaction

The correct structure has been established for the compound obtained on the treatment of the methyl ester of gibberellin A3 with zinc in boiling acetic anhydride, to which the erroneous structure (II) was previously assigned. A mechanism of the formation of compound (II) is suggested which includes an intramolecular diene condensation between an acetate carbonyl group and the conjugated diene system in the intermediate mixed anhydride (V).

Unsaturated Sugars : An Alternative Route to 3, 5, 6-Trideoxy-1, 2-O-Isopropylidene-α-D-Glycero-Hex-3, 5-Dienofuranose

Abstract Unsaturated sugars are among the most important and useful compounds in carbohydrate chemistry. They assume key roles in the synthesis of modified sugars and complex natural products. The title compound 5, an unsaturated sugar containing a conjugated diene system, has been reported1 recently and its potential synthetic value for Diels-Alder reaction giving access to functionalized annulated furanoses has been pointed out.2 For a different synthetic purpose we prepared this compound by an alternative route albeit from the same starting material used by the previous authors. Our synthetic sequence is outlined in the following scheme.

Functionalization at the double bond region of jojoba oil: I. bromine derivatives

AbstractAddition of bromine to jojoba oil and itstrans‐isomer yielded tetrabromojojoba, which upon elimination afforded the acetylenic and allenic components, respectively, when reacted with excess of base. The bromoolefinic products were obtained when limited amount of base was used. Allylic bromination of the liquid wax and itstrans‐isomer, and subsequent HBr elimination, yielded the two conjugated diene systems on both parts of the ester (jojoba tetraene).

Hydrogenation of conjugated double bonds of trans-1,3-pentadiene catalysed by Rh 2Cl 2(CO) 4 in solution and anchored to γ-Al 2O 3

Hydrogenation under mild conditions (1 atm H 2 and 60–80°C) of trans1,3-pentadiene catalysed by Rh 2Cl 2(CO) 4 in toluene solution and by Rh 2Cl 2(CO)4 anchored on γ-Al 2O 3 has been investigated. Both the homogeneous and the heterogenised catalysts display a good specificity towards hydrogenation of the external double bond of the conjugated diene system. A slow inactivation of the supported catalyst occurs during the hydrogenation, but it cannot be attributed to reaction of the catalyst with the substrate since it occurs also when Rh 2Cl 2(CO) 4 is heated at 70°C under 1 atm H 2. Partial substitution of CO ligands of Rh 2Cl 2(CO) 4 by triphenylphosphine leads to a reduction of the activity of the homogeneous catalyst but does not alter its specificity. Triphenylphosphine can either increase or decrease the activity of the heterogenised catalyst depending on whether its introduction into the system precedes or follows the anchorage of Rh 2Cl 2(CO) 4 on Al 2O 3.

Nuclear magnetic resonance spectroscopy of sterols. 13C olefinic carbon shieldings in sterols and related cyclic compounds

This study concerns detailed analyses of olefinic carbon shieldings in sterols and related cyclic olefins. Included are detailed considerations of olefinic carbon shieldings in mono-unsaturated sterols and related compounds and in sterols containing homoannular and heteroannular conjugated diene systems. In addition, allylic and homoallylic shielding effects on quaternary, methine, methylene, and methyl carbon atoms in these systems have been subjected to detailed analyses.

Cyclo-adducts of thebaine with nitrosoarenes

Thebaine (1) reacts reversibly with various nitroso-arenes to form cyclo-adducts by 1,4-addition of the nitrosogroup to the conjugated diene system of the alkaloid. Adducts (2) of thebaine with nitrosobenzene and with 4-chloro-, 4-methyl-, 3-methoxy-, and 4-nitro-nitrosobenzene have been prepared in good yield. The adduct with nitrosobenzene was hydrolysed by hydrochloric acid to give 14β-(N-hydroxyphenylamino)codeinone (3; Ar = Ph) in high yield. Catalytic hydrogenation of this derivative afforded 7,8-dihydro-14β-phenylaminocodeinone (4). 14β-(N-Hydroxyphenylamino)codeinone rearranged readily in alkaline solution to give the phenol, 5,O-dihydro-5β,14β-(N-phenylepoxyimino)codeinone (5).

Reactivity of monoenic and conjugated diene systems present in unsaturated olefin terpolymers—II. Reactions with methyl radicals

The experimental rate constants for the reactions of methyl radicals with model compounds simulating ethylidene-norbornene (ENB), methylene-norbornene (MNB) and isopropylidene-dicyclopentadiene (IPDCP) units in EPDM and EPTM elastomers are reported. These constants, as well as others reported in a previous paper or derived from the literature, have been used to perform a kinetic analysis of the grafting of styrene onto EPM, EP-ENB or EP-IPDCP in inert solvent. The systems of kinetic differential equations have been solved by numerical integration without steady state approximation. Valuable information has been obtained on the role of the nature of radical initiators and the sensitivity of the results to change with constants in the various steps.

ChemInform Abstract: CHIRAL ACETYLENES AS SYNTHETIC INTERMEDIATES. II. OPTICALLY ACTIVE 1,4‐DIALKYLBUTA‐1,3‐DIENES: SYNTHESIS AND CONFORMATIONAL STUDIES

Abstract The synthesis and the physical properties of some optically active 1,4-dialkylbuta-1,3-dienes are reported. The synthetic processes employed were essentially stereospecific. NMR, UV and CD spectra of these compounds provide information on the main conformation of the conjugated diene system, which was shown to be s-trans planar.

Formation of a terminal conjugated diene system by the palladium catalyzed elimination reactions of allylic acetates and phenyl ethers

Bei der Behandlung mit Palladiumacetat und Triphenylphosphin erhalt man aus den isomeren Allylalkohol- Derivaten (I) bzw. (II) die Diene (III).