Straightforward Preparation of (2E,4Z)-2,4-Heptadien-1-ol and (2E,4Z)-2,4-Heptadienal

Abstract

A concise synthesis of (2E,4Z)-2,4-heptadien-1-ol and (2E,4Z)-2,4-heptadienal is presented. Commercially available (Z)-2-penten-1-ol was converted to ethyl-(2E,4Z)-2,4-heptadienoate by reaction with activated MnO₂ and (carboethoxymethylene)triphenylphosphorane in the presence of benzoic acid as a catalyst. Ethyl-(2E,4Z)-2,4-heptadienoate was converted to (2E,4Z)-2,4-heptadien-1-ol with LiAlH₄. The alcohol was partially oxidized to (2E,4Z)-2,4-heptadienal with MnO₂. The title compounds are male-specific, antennally active volatile compounds from the Saltcedar leaf beetle, Diorhabda elongata Brulle (Coleoptera: Chrysomelidae) and have potential use in the biological control of the invasive weed saltcedar (Tamarix spp).     

Chiral [2H]-Labelled Methylene Groups in Trienoic- and Dienoic Fatty Acids: A Facile Approach via Asymmetric Epoxidation of [2H] Allyl Alcohols

Chiral [²H] -labelled methylene groups flanked by two double bonds within (poly)unsaturated fatty acids are readily available from trans-2,3-epoxy[2,3-²H₂] alk-4-yn-l-ols, obtained in their turn by asymmetric epoxidation of the corresponding (E)-[2,3-²H₂] alk-2-en-4-yn-l-ols (see Scheme 3). The procedure is exemplified for (8S,3Z,6Z,9Z)-[7,8-²H₂] trideca-3,6,9-trienoic acid ((8S)- 11 ) and (8R)- 11 (Scheme 4) as well as for (5S,3Z,6Z)-[4,5^?2H₂]deca-3,6-dienoic acid ((5S)- 13 ) and (5R)- 13 (Scheme 5).     

Conformational Properties of (Z,Z)-, (E,Z)-, and (E,E)-Cycloocta-1,4-dienes

Summary.  Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and the MP2/6-31G^*//HF/6-31G^* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C ₂-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C _S-symmetric boat-boat geometry is 19.1 kJ·mol⁻¹. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C ₁) transition state which is 43.5 kJ·mol⁻¹ above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol⁻¹ more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol⁻¹, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol⁻¹. The C _S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C _S) transition state which is 37.2 kJ·mol⁻¹ above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol⁻¹ less stable than the crown conformation. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 3, 2002     

The Isotopomeric (Z)- and (E)-2,3-Dimethyl(1,1,1,4,4,4-2H6)but-2-enes: Mechanistic Probes for Stereospecific Epoxidation

By unambiguous methods, (Z)- and (E)-2, 3-dimethyl(1, 1, 1, 4, 4, 4-²H₆)but-2-enes ( 3 ) were synthesized and transformed to the epoxides 4 with 3-chloroperbenzoic acids. Both the isotopomeric olefins and the epoxides are detected separately by ¹H-NMR at 400 MHz. Epoxidation of (Z)- 3 with [Rh^ICl(PPh₃)₃]/cumene hydroperoxide resulted in a 1: 1 mixture of (Z)- and (E)- 4 , while reaction of (Z)- 3 with [Fe^III(tpp)]Cl/PhIO gave only (Z)- 4 (tpp = tetraphenylporphyrin).     

The Photoisomerization Behavior of the (4-Hydroxycinnamoyl)-spermidines

The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2 , and 3 , and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5 , and 6 , are investigated. The synthetic product (E)- 1 could be almost quantitatively (> 96%) converted into its isomer (Z)- 1 under UV light irradiation. In the cases of (E)- 2 and (E)- 3 , a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C?C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)- 4 , (Z,Z)- 5 , and (Z,Z)- 6 . Nevertheless, the fractions of (Z,Z)- 5 and (Z,Z)- 6 were in almost pure state collected, and their ¹-NMR spectra are presented.     

Reduktion von 1,2-bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzol: Synthese von Cyclotrisazobenzol ( = (5E,6aZ,11E,12aZ,17E,18aZ)-5,6,11,12,17,18-Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca-hexaen)

Reduction of 1,2-Bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene¹: Synthesis of Cyclotrisazobenzene ( = (5E,6aZ,11E,12aZ,17E,18aZ)-5,6,11,12,17,18-Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca-hexaene) Na₂S reduction of 1,2-bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene ( 2 ) yielded 3 deoxygenated products: the (known) red 2,2′-((E,E)-1,2-phenylenbisazo)dianiline ( 3 , 23%), the orange 2-[2-((E)-2-aminophenylazo)phenyl]-2H-benzotriazol ( 4 , 55%) and the colorless 2,2′-(1,2-phenylene)di-2H-benzotriazol ( 5 , 13%). The constitutions of 3 – 5 and of 6 , the N-acetyl derivative of 4 , were deduced from their ¹H-NMR spectra (chemical shifts, couplings, and symmetry properties), and the configurations of 3 , 4 , and 6 at their N,N-double bonds are assumed to be the same as in 2 . Oxidation of 3 with 2 mol-equiv. of Pb(OAc)₄ afforded 5 (47%) and a novel, highly symmetrical macrocycle, called cyclotrisazobenzene ( 7 , 24%). The constitution of 7 as a tribenzo-hexaaza[12]annulene and its (E)-configuration at the N,N-bonds was confirmed by X-ray analysis. The molecular symmetry expressed by the ¹H-, ¹³C- and ¹⁵N-NMR spectra of 7 reveals a rapid torsional motion around the six N,C bonds. This implies that the N,N-double bonds in the cyclic 12π-electron system (or 24π-electron system if the benzene rings are included) of 7 are highly localized.     

Biosynthesis of Dodecano-4-lactone in Ripening Fruits: Crucial Role of an Epoxide-Hydrolase in Enantioselective Generation of Aroma Components of the Nectarine (Prunus persica var. nucipersica) and the Strawberry (Fragaria ananassa)

Early steps in the biosynthesis of dedecano-4-lactone in ripening nectarines (Prunus persica var. nucipersica) and strawberries (Fragaria ananassa) were studied using cis-9,10-([¹⁸O]epoxy)heptadecanoic acid ( 5 ), instead of the natural C₁₈-precursor epoxystearic acid 1 . In nectarines, an epoxide hydrolase catalyzed, in a highly regio- and enantioselective reaction, the attack of H₂O at C(9) of epoxy acid 5 yielding preferentially (9R,10R)-dihydroxyheptadecanoic acid 6a as an early intermediate and, after further metabolization, undecano-4-lactone 7a . In strawberries, the same transformation exhibited only a moderate regio- and enantioselectivity. Besides the previously established function of phytogenic epoxide hydrolases involved in generating oxygenated fatty-acid derivatives, which are used in cutin monomer production and plant defence, a new rǒle for these enzymes now emerges in the enantioselective production of aroma components of ripening fruits. The cis-9,10-([¹⁸O]epoxy)heptadecanoic acid (≥ 98% ¹⁸O; 5 ) was obtained in good overall yield (68%) from isopropyl (9Z)-heptadec-9-enoate using ¹⁸O₂ gas in a free-radical chain reaction in the presence of 2-methylbutanal.     

Sterospecific Syntheses and Spectroscopic Properties of Isomeric 2,4,6,8-Undecatetraenes. New Hydrocarbons from the Marine Brown Alga Giffordia mitchellae. Part IV.

Giffordene (=(2Z,4Z,6E,8Z)-2,4,6,8-undecatetraene; 9f ) and five steroisomers are new C₁₁H₁₆ hydrocarbons from the marine brown alga Giffordia mitchellae. Their synthesis is based on non-stereoselective Wittig reactions of (E)-2-alkenals with appropriate acetylenic phosphoranes and subsequent chromatographic separation of the resulting (E/Z)-pairs. The uniform enynes (>98% purity) are then stereospecifically reduced to (Z)-alkenes with Zn(Cu/Ag) in aq. MeOH at r.t. ¹³C- and ¹ H-NMR data of the new tetraenes are presented. Biosynthetically, giffordene ( 9f ) originates from dodeca-3,6,9-trienoic acid via an unstable (3Z,5Z,8Z)-1,3,5,8,-undecatetraene followed by a thermally allowed antarafacial 1,7-sigmatropic hydrogen shift to the (2Z,4Z,6E,8Z)-isomer 9f .     

Singlet-Oxygen Ene Reactions of (E)-4-Propyl[1,1,-2H3]oct-4-ene. Short Communication

Rose bengal-sensitized photooxygenation of 4-propyl-4-octene ( 1 ) in MeOH/Me₂CHOH 1:1 (v/v) and MeOH/H₂O 95:5 followed by reduction gave (E)-4-propyl-5-octen-4-ol ( 4 ), its (Z)-isomer 5 , (E)-5-propyl-5-octen-4-ol ( 6 ), and its (Z)-isomer 7 . Analogously, (E)-4-propyl[1,1,1-²H₃]oct-4-ene ( 2 ) gave (E)-4-propyl[1,1,1-²H₃]oct-5-en-4-ol ( 14 ), its (Z)-isomer 15 , (E)-5-[3′,3′,3′-²H₃]propyl-5-octen-4-ol ( 16 ), its (Z)-isomer 17 , and the corresponding [8,8,8-²H₃]-isomers 18 and 19 (see Scheme 1). The proportions of 4–7 were carefully determined by GC between 10% and 85% conversion of 1 and were constant within this range. The labeled substrate 2 was photooxygenated in two high-conversion experiments, and after reduction, the ratios 16/18 and 17/19 were determined by NMR. Isotope effects in 2 were neglected and the proportions of corresponding products from 1 and 2 assumed to be similar (% 4 ≈? % 14 ; % 5 ≈? % 15 ; % 6 ≈? % ( 16 + 18 ): % 7 ≈? % ( 17 + 19 )). Combination of these proportions with the ratios 16/18 and 17/19 led to an estimate of the proportions of hydroperoxides formed from 2 . Accordingly, singlet oxygen ene additions at the disubstituted side of 2 are preferred (ca. 90%). The previously studied trisubstituted olefins 20–25 exhibited the same preference, but had both CH₃ and higher alkyl substituents on the double bond. In these substrates, CH₃ groups syn to the lone alkyl or CH₃ group appear to be more reactive than CH₂ groups at that site beyond a statistical bias.     

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).     

Studies on chiral thiophosphoric acids and their derivatives: 4. The stereospecific synthesis of optically active O-ethyl O-phenyl O-(1-methyl-2-ethoxycarbonyl) vinyl phosphorothionate

The stereoisomers (3 and 4) of O-ethyl O-phenyl O-(1-methyl-2-ethoxycarbonyl) vinyl phosphorothionate have been synthesized by the reaction of optically active O-ethyl O-phenyl phosphorothiochloride 2 with ethyl acetoacetate under different conditions. 3 (100% Z-isomer, determined by ¹H NMR) was synthesized by the reaction of 2 with ethyl sodio-acetoacetate in the mixed solvent of 1:3 toluene-dioxane at 50°C. 4 (>95% E-isomer) was obtained by the reaction of 2 with ethyl acetoacetate in presence of t-BuOK in DMSO at 15°C. 100% E-isomer 4 was separated from crude 4(>95% E-isomer) by column chromatography on silica gel (petroleum ether-ether 6:1). By this reaction either Z- or E-isomers were formed with inversion of the configuration at phosphorus atom. Thus, six stereoisomers of 3 and 4 which were prepared from 2 (RS, S, R) by the above method namely (RS)-Z, (R)-Z, (S)-Z and (RS)-E, (R)-E, (S)-E.     

Light-Controlled Destruction and Assembly: Switching between Two Differently Composed Cage-Type Complexes

We report on two regioisomeric, diazocine ligands 1 and 2 that can both be photoswitched between the E- and Z-configurations with violet and green light. The self-assembly of the four species ( 1 -Z, 1 -E, 2 -Z, 2 -E) with Co^II ions was investigated upon changing the coordination vectors as a function of the ligand configuration (E vs Z) and regioisomer ( 1 vs 2 ). With 1 -Z, Co₂( 1 -Z)₃ was self-assembled, while a mixture of ill-defined species (oligomers) was observed with 2 -Z. Upon photoswitching with 385 nm to the E configurations, the opposite was observed with 1 -E forming oligomers and 2 -E forming Co₂( 2 -E)₃. Light-controlled dis/assembly was demonstrated in a ligand competition experiment with sub-stoichiometric amounts of Co^II ions; alternating irradiation with violet and green light resulted in the reversible transformation between Co₂( 1 -Z)₃ and Co₂( 2 -E)₃ over multiple cycles without significant fatigue by photoswitching.     

Synthesis of the (Z) and (E) isomers of 1,2-diaryl-3-methyl-4,5-dioxo-3-pyrrolidinecarboxylic acid esters. Structural assignment by nmr and mass spectroscopy

Reaction of N-benzylideneaniline, 1a , with 3-methyl-2-oxobutanedioic acid diethyl ester, 2a , produced isomeric 3-methyl-4,5-dioxo-1,2-diphenyl-3-pyrrolidinecarboxylic acid ethyl esters, 3a and 3b . The higher melting isomer, 3a , was shown to have the (Z) configuration by nmr spectroscopy. The (Z) and (E) isomers of 3-methyl-4,5-dioxo-1,2-diphenyl-3-pyrrolidinecarboxylic acid methyl esters, 3c and 3d , were prepared from 1a and 3-methyl-2-oxobutanedioic acid dimethyl ester, 2b . The higher melting isomer, 3c , was shown to have the (Z) configuration. Similarly, N-benzylidene-p-toluidine, 1b , reacted with 2a to form (Z) and (E) isomers of 3-methyl-4,5-dioxo-1-(4-methylphenyl)-2-phenyl-3-pyrrolidinecarboxlic acid ethyl esters, 3e and 3f . Assignment of the ¹³C carbonyl carbon nmr chemical shift was made by preparing 2-methyl-3-oxobutanedioic-1-¹³C acid diethyl ester, 4 , and from it the corresponding (Z) and (E) isomers of 3-methyl-4,5-dioxo-1,2-diphenyl-3-pyrrolidinecarboxylic ¹³C acid ester, 5a and 5b . The mass spectra of the (Z) isomers exhibit prominent ions corresponding to the masses of the Schiff bases used to make them, and ions corresponding to the loss of ArNCOCO from the parent ion. The (E) isomers 3b, 3d and 5b exhibit a prominent ion of mass 264; 3f gives mass 278, corresponding to the loss of the carboalkoxy group.     

Synthese von enantiomerenreinem Mimulaxanthin und seiner (9Z,9′Z)- und (15Z)-Isomeren

Synthesis of Enantiomerically Pure Mimulaxanthin and of Its (9Z,9′Z)- and (15Z)Isomers We present the details of a synthesis of optically active, enantiomerically pure stereoisomers of mimulaxanthin (=(3s,5R,6R,3′S,5′R,6′R)-6,7,6′,7′-tetradehydro-5,6,5′,6′-tetrahydro-β,β-carotin-3,5,3′,5′-tetrol) either as free alcohols 1a and 24a or as their crystalline (t-Bu)Me₂Si ethers 1b and 24b . Grasshopper ketone 2a , a presumed synthon, unexpectedly showed a very sluggish reaction with Wittig-Horner reagents. Upon heating with the ylide of ester phosphonates, an addition across the allenic bond occurred. On the contrary, a slow but normal 1,2-addition took place with the ylide from (cyanomethyl)phosphonate but, unexpectedly, with concomitant inversion at the chiral axis. So a mixture of(6R,6S,9E,9Z)-isomers 6 – 9 was produced {(Scheme 1). However, a fast and very clean 1,2-addition occurred with the ethynyl ketone 12 to yield the esters 13 and 14 (Scheme 2). DIBAH reduction of the separated stereoisomers gave the allenic alcohols 15 and 16 in high yield. Mild oxidation to the aldehydes 17 and 18 followed by their condensation with the acetylenic C₁₀-bis-ylide 19 led to the stereoisomeric 15,15′-didehydromimulaxanthins 20 and 22 , respectively (Schemes 3 and 4). Mimulaxanthins 1 and 24 were prepared by partial hydrogenation of 20 and 22 followed by a thermal (Z/E)-isomerization. As expected, the mimulaxanthins exhibit very weak CD curves, obviously caused by the allenic bond that insulates the chiral centers in the end group from the chromophor. On the contrary, some of the C₁₅-allenic synthons showed not only fairly strong CD effects but also a split CD curve which, in our interpretation, results from an exciton coupling between the allene and the C(9)?C(10) bond. We postulate a rotation around the C(8)? C(9) bond, presumably caused by an intramolecular H-bond in 16 or by a dipol interaction between the polarized double bonds in 6 , 7 , 8 , and 17 .     

Preparation and X-Ray Study of Inclusion Complexes of (4Z,5E)-Pyrimidine-2,4,5,6(1 H,3H)-Tetraone 4,5-Dioxime and the Product of Its Cyclization, (1,2,5)-Oxadiazolo(3,4-d)-Pyrimidine-5,7(4 H,6H)-Dione with Two 18-Membered Macrocycles

The novel dioxime, (4Z,5E)-pyrimidine-2,4,5,6(1H,3H)-tetraone 4,5-dioxime (H₂-PTD) was obtained by the interaction of 6-amino-5-nitrosopyrimidine-2,4(1H,3H)-dione with hydroxylamine hydrochloride. X-ray structural analysis determined the 4Z,5E-configuration of the corresponding monoanion, pyrimidine-2,6(1H,3H)-dione-4-iminole-5-iminolate in the inclusion complexes with diazonia-18-crown-6 (1,4,10,13-tetraoxa-7,16-diazoniacyclooctadecane) (H₂-DA18C6)²⁺ (complex (1), stoichiometry 2 : 1), and its ammonium salt in the complex with the cis-syn-cis isomer of dicyclohexano-18-crown-6(DCHA) (cis-syn-cis-2,5,8,15,18,21-hexaoxatricyclo (20.4.0.0^9,14)hexacosane) (complex (2), stoichiometry 1 : 1). X-ray data were also obtained for the complex of the product of (H₂-PTD) cyclization, (1,2,5)-oxadiazolo(3,4-d)pyrimidine-5,7(4H,6H)-dione (OPD) with diaqua diaza-18-crown-6 (complex (3), stoichiometry 2 : 2 : 1).In (1) the (H-PTD)^- anions are joined into dimers through the bifurcated OH...N and OH...O hydrogen bonds and alternate with diazonia-18-crown-6 cations in the chains sustained by the NH(crown) ... O and NH(crown) ...N interactions. The chains are further combined into the 3D network via NH...O(crown) hydrogen bonds. In (2) the self-complementarity of the (H-PTD)^- anions facilitates their assembly into the chain via OH...N, NH...O and OH...O interactions. The ammonium cations bridge each anion and the DCHA macrocycle with the formation of a ribbon developed along the [101] direction in the unit cell. Ternary complex (3) is built of the neutral species, diaza-18-crown-6, water molecules and dimers of OPD alternated in the chains and held together by OH...O and NH...O hydrogen bonds.     

Thermische (E), (Z)-Isomerisierungen bei substituierten Propenylbenzolen

Thermal (E), (Z)-Isomerizations of Substituted Propenylbenzenes The thermal isomerizations of (E)- and (Z)-3,5-dimethyl-2-(1′-propenyl)phenol ((E)- and (Z)- 3 ), (E)- and (Z)-N-methyl-2-(1′-propenyl)anilin ((E)- and (Z)- 4 ), (E)- and (Z)-3,5-dimethyl-2-(1′-propenyl)anilin ((E)- and (Z)- 5 , (E)- and (Z)-2-(1′-propenyl)mesitylene ((E)- and (Z- 6 ), (E)- and (Z)-2-(1′-propenyl)mesitylene ((E)- and (Z)- 7 ), (E)- and (Z)-2-(1′-propenyl)toluene ((E)- and (Z)- 8 ), (E)- and (Z)-4-(1′-propenyl)toulene ((E)- and (Z)- 9 ) as well as of (E)- and (Z)-2-(2′-butenyl)-mesitylene ((E)- and (Z)- 10 ) in decane solution were studied (Scheme 2). Whereas the isomerization of the 2-propenylphenols (E)- and (Z)- 3 occurs already between 130 and 150° (cf. Table 1), the isomerization of the 2-propenylanilins 4 and 5 takes place only at temperatures between 220 and 250° (cf. Tables 2 and 3). The activation values and the experiments using N-deuterated 4 (cf. Scheme 4) show that 2-propenylphenols and -anilins isomerize via sigmatropic [1,5]-hydrogen-shifts. For the isomerization of the methyl-substituted propenylbenzenes temperatures > 360° are required (cf. Tables 4 and 5). The activation values of the isomerization of (E)- and (Z)- 6 and (E)- and (Z)- 9 are in accord with those of other (E), (Z)-isomerizations which occur via vibrationally excited singlet biradicals (cf. Table 7). Nevertheless, thermal isomerization of 2′-d-(Z)- 8 (cf. Scheme 6) demonstrates that during the reaction deuterium is partially transfered into the ortho-methyl group, i.e. 1,5-hydrogen-shifts must have participated in isomerization of (E)- and (Z)- 8 (cf. Scheme 8). Under the equilibrium conditions 2,4,6-trimethylindan ( 17 ) is formed slowly at 368° from (E)- and (Z)- 6 , very probably via a radical 1,4-hydrogen-shift (cf. Scheme 9). In a similar way 2-ethyl-4,6-dimethylindan ( 19 ; cf. Table 6) arises from (E)- and (Z)- 7 . Thermolysis of (E)- and (Z)- 10 in decane solution at 367° results in almost no (E),(Z)-isomerization. At prolonged heating 19 and 2,5,7-trimethyl-1,2,3,4-tetrahydronaphthalene ( 20 ) are formed; these two products arise very likely from an intermolecular radical process (cf. Scheme 10).     

Stereocontrolled synthesis of (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols,intermediates in the synthesis of strobilurin antibiotics

(2E,4E)-5-Aryl-2-(2-benzyloxyethyl)penta-2,4-dien-1-als (aryl is phenyl and 4-methox-yphenyl) were reduced with NaBH₄ quantitatively and stereospecifically to the corresponding penta-2(E),4(E)-dien-1-ols. The hydroxymethyl group in the latter was transformed into a methyl one with a stereoselectivity of 92–97%. Debenzylation of the resulting (1E,3Z)-1-aryl-6-benzyloxy-4-methylhexa-1,3-dienes with AlCl₃ in the presence of PhNMe₂ afforded the target (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols; the configuration of the C=C bonds in the conjugated aryl diene systems was retained at 95%.     

Preparation and (E/Z)‐Isomerization of the Diastereoisomers of Violaxanthin

Violaxanthin A (=(all‐E,3S,5S,6R,3′S,5′S,6′R)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol =syn,syn‐violaxanthin; 5 ) and violaxanthin B (=(all‐E,3S,5S,6R,3′S,5′R,6′S)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol=syn,anti‐violaxanthin; 6 ) were prepared by epoxidation of zeaxanthin diacetate ( 1 ) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I₂‐catalyzed photoisomerization. The structure of the main products, i.e., (9Z)‐ 5 , (13Z)‐ 5 , (9Z)‐ 6 , (9′Z)‐ 6 , (13Z)‐ 6 , and (13′Z)‐ 6 , was determined by their UV/VIS, CD, ¹H‐NMR, ¹³C‐NMR, and mass spectra.     

(E/Z)‐Isomerization of (all‐E)‐5,6‐Diepikarpoxanthin

(all‐E)‐5,6‐Diepikarpoxanthin (=(all‐E,3S,5S,6S,3′R)‐5,6‐dihydro‐β,β‐carotene‐3,5,6,3′‐tetrol; 1 ) was submitted to thermal isomerization and I₂‐catalyzed photoisomerization. The structures of the main products, i.e. (9Z)‐ ( 2 ), (9′Z)‐ ( 3 ), (13Z)‐ ( 4 ), (13′Z)‐ ( 5 ), and (15Z)‐5,6‐diepikarpoxanthin ( 6 ), were determined by their UV/VIS, CD, ¹H‐NMR, and mass spectra. In addition, (9Z,13′Z)‐ or (13Z,9′Z)‐ ( 7 ), (9Z,9′Z)‐ ( 8 ), and (9Z,13Z)‐ or (9′Z,13′Z)‐5,6‐diepikarpoxanthin ( 9 ) were tentatively identified as minor products of the I₂‐catalyzed photoisomerization.     

Sarcodictyin A and Sarcodictyin B,Novel Diterpenoidic Alcohols Esterified by (E)-N(1)-Methylurocanic Acid. Isolation from the Mediterranean Stolonifer Sarcodictyon roseum

The Mediterranean stolonifer Sarcodictyon roseum (= Rolandia rosea) (Cnidaria, Anthozoa, Alcyonaria, Stolonifera, Clavulariidae) is shown to contain two novel diterpenoidic alcohols esterified by (E)-N(1)-methyl-urocanic acid (= E)-3-(l-methyl-lH-imidazol-4-yl)acrylic acid). They are sarcodictyin A ( = (?)-(4R,4a,R, 7R,10S,11S,12aR,lZ,5E,8Z)-7,10-epoxy-3,4,4a,7,10,11,12,12a-octahydro-7-hydroxy-6-(methoxycarbonyl)-1,10-dimethyl-4-(1-methylethyl)benzocyclodecen-11-yl (E)-3-(1-methyl-lH-imidazol-4-yl)acrylate; (?)- 1 ) and sarco-dictyin B (the 6-(ethoxycarbonyl analogue; (?)- 2 ). The assignment of the structures is mainly based on 1D- and 2D-NMR data, as well as on chemical transformations of (?)- 1 , such as transesterification with MeONa/MeOH giving methyl (E)-N(1)-methylurocanate ( 3 ) and the free alcohol (+)- 4 and reduction with LiAlH₄ followed by benzoylation giving dibenzoate 7. Absolute configurations are based on Horeau's method of esterification of (+)- 4 .