(1E,3E,5E)‐1,2,3,4,5,6‐Hexa­fluoro‐1,6‐di­phenyl­hexatriene

The title triene, C₁₈H₁₀F₆, was prepared via the Pd⁰ coupling reaction of (E)‐(1,2‐di­fluoro‐1,2‐ethenediyl)­bis­(tri­butyl­stan­nane) with (Z)‐β‐iodo‐α,β‐di­fluoro­styrene in N,N′‐dimethylformamide/tetrahydrofuran. The crystal structure shows the product to be the 1E,3E,5E isomer. Due to steric interactions between F atoms, the double bonds are not coplanar. The planes defined by the two terminal double bonds are almost perpendicular.     

(E,E,E)‐1,6‐Bis(2,4‐di­chloro­phenyl)­hexa‐1,3,5‐triene

The title mol­ecule, C₁₈H₁₂Cl₄, lies about an inversion centre and the hexatriene chain is planar. The torsion angle of the single bond between the planes of the chain and the benzene ring is −8.6 (3)°. The dihedral angle between the planes defined by the chains of adjacent mol­ecules is 50.0 (2)°. The shortest intermolecular distance between the Cl atoms is 3.514 (1) Å. The mol­ecules are joined through π–π‐stacking and strong attractive Cl⃛Cl interactions.     

(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.     

1,2,3‐Trimethoxy‐4‐[(E)‐2‐phenylvinyl]benzene and (E,E)‐1,4‐bis(2,3,4‐trimethoxyphenyl)buta‐1,3‐diene

The stilbene derivative 1,2,3‐trimethoxy‐4‐[(E)‐2‐phenylvinyl]benzene, C₁₇H₁₈O₃, (I), and its homocoupling co‐product (E,E)‐1,4‐bis(2,3,4‐trimethoxyphenyl)buta‐1,3‐diene, C₂₂H₂₆O₆, (II), both have double bonds in trans conformations in their conjugated linkages. In the structure of stilbene (I), the aromatic rings deviate significantly from coplanarity, in contrast with coproduct (II), the core of which is rigorously planar. The deviation in stilbene (I) seems to be driven by intermolecular electrostatic interactions. Diene (II) sits on a crystallographic inversion centre, which bisects the conjugated linkage.     

Synthesis of 32‐phenyl‐substituted methyl E/Z‐pyropheophorbide‐a's from methyl E/Z‐pyropehophorbide‐a 131‐ketoximes

Methyl E/Z‐pyropheophorbide‐a 13¹‐ketoximes 2a,b and their O‐acetyl derivatives 3a,b were oxidized with osmium(VIII) oxide to give aldehydes 4a,b and 5a,b , respectively. The Wittig reactions of the aldehyde chlorines 4a,b and 5a,b with benzyltriphenylphosphonium chloride were performed to form the corresponding methyl (3¹E/Z,13¹E/Z)‐3²‐phenylpyropheophorbide‐a 13¹‐ketoximes 6aa‐bb and their O‐acetyl derivatives 7aa‐bb ; hydrolysis of these ketoximes 6aa,ba and 6ab,bb in formic acid produced methyl (E/Z)‐3²‐phenylpyropheophorbide‐a's 8a,b .     

Iodination of cyclo‐E5‐Complexes (E=P,As)

In a high‐yield one‐pot synthesis, the reactions of [Cp*M(η⁵‐P₅)] (M=Fe ( 1 ), Ru ( 2 )) with I₂ resulted in the selective formation of [Cp*MP₆I₆]⁺ salts ( 3 , 4 ). The products comprise unprecedented all‐cis tripodal triphosphino‐cyclotriphosphine ligands. The iodination of [Cp*Fe(η⁵‐As₅)] ( 6 ) gave, in addition to [Fe(CH₃CN)₆]²⁺ salts of the rare [As₆I₈]^2? (in 7 ) and [As₄I₁₄]^2? (in 8 ) anions, the first di‐cationic Fe‐As triple decker complex [(Cp*Fe)₂(μ,η^5:5‐As₅)][As₆I₈] ( 9 ). In contrast, the iodination of [Cp*Ru(η⁵‐As₅)] ( 10 ) did not result in the full cleavage of the M?As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)₂(μ,η^5:5‐As₅)][As₆I₈]_0.5 ( 11 ) represents the first Ru‐As₅ triple decker complex, thus completing the series of monocationic complexes [(Cp^RM)₂(μ,η^5:5‐E₅)]⁺ (M=Fe, Ru; E=P, As). [(Cp*Ru)₂As₈I₆] ( 12 ) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)₂As₄I₄] ( 13 ) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.     

(E)‐N‐Benzyl­idene‐3‐chloro‐4‐fluoro­aniline

The title mol­ecule, C₁₃H₉ClFN, is substantially planar. The phenyl and 3‐chloro‐4‐fluoro­phenyl rings are on opposite sides of the C=N bond. There is an intermolecular C—H?F short contact with a C?F distance of 3.348 (2) Å and a C—H?F angle of 137.4 (1)°. The mol­ecules are held in layers parallel to the bc plane.     

Conformational polymorphism of (E,E)‐N,N′‐bis(4‐nitrobenzylidene)benzene‐1,4‐diamine

Two polymorphs of (E,E)‐N,N′‐bis(4‐nitrobenzylidene)benzene‐1,4‐diamine, C₂₀H₁₄N₄O₄, (I), have been identified. In each case, the molecule lies across a crystallographic inversion centre. The supramolecular structure of the first polymorph, (I‐1), features stacking based on π–π interactions assisted by weak hydrogen bonds involving the nitro groups. The second polymorph, (I‐2), displays a perpendicular arrangement of molecules linked via the nitro groups, combined with weak C—H...O hydrogen bonds. Both crystal structures are compared with that of the carbon analogue (E,E)‐1,4‐bis[2‐(4‐nitrophenyl)ethenyl]benzene, (II).     

(E,E,E)‐1,3,5‐Tris[4‐(acetyl­sulfan­yl)­styr­yl]­benzene toluene hemisolvate

The first crystal structure of a three‐terminal sulfur end‐capped oligo­phenyl­ene­vinyl­ene, C₃₆H₃₀O₃S₃·0.5C₇H₈, has been determined at 122 (1) K. The mol­ecular threefold symmetry is not utilized in the crystal structure. It is confirmed that the double bonds have been fully transformed into a trans configuration by iodine treatment.     

Two‐step Synthesis of New γ‐Lactones via Cyclization of 7‐Chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐(2E,4E,6E)‐trienoic acid

A new rapid synthesis of γ‐lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7‐chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐7‐phenyl (or methyl) (2E,4E,6E)‐trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π_2s + π_2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half‐esters since; if the cyclization obeys to the proposed mechanism, the diacids, half‐esters must also cyclize in a similar manner. Saponification of these led to γ‐dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated.     

(E,E)‐2,5‐Diprop­oxy‐1,4‐bis­[2‐(2,4,6‐trimethoxy­phen­yl)ethen­yl]benzene

The title compound, C₃₀H₃₄O₈, crystallizes in the space group P with one‐half of a mol­ecule in the asymmetric unit. A three‐dimensional network is generated by OCH₃⋯π and CH⋯π inter­actions. The conformation of the C—C bond exocyclic to the central benzene ring is different from that of every other known derivative. A comparison of the geometry of the title mol­ecule and of its solid‐state structure with other 2,4,6‐trimeth­oxy‐substituted PPV [i.e. poly(p‐phenylenevinylene)] oligomers, in particular the isoprop­oxy‐substituted compound, is provided.     

(2S,RS)‐6‐Phenyl‐1‐(p‐tolyl­sulfinyl)­hexa‐3(E),5(E)‐dien‐2‐ol

The mol­ecule of the title compound, C₁₉H₂₀O₂S, corresponds to a chiral sulfinyldienol with two stereogenic centres, viz. the C atom susbtituted by the hydr­oxy group and the sulfinyl S atom. The mol­ecule displays a V‐shape in the solid state. The dihedral angle defined by the least‐squares planes of the aromatic rings is 72.9 (1)°. The packing pattern exhibits the following inter­molecular hydrogen bonds: one O—H⋯O [H⋯O = 1.98 Å, O⋯O = 2.785 (4) Å and O—H⋯O = 166°] and two C—H⋯O [H⋯O = 2.58 and 2.60 Å, C⋯O = 3.527 (5) and 3.347 (5) Å, and C—H⋯O = 164 and 134°]. These define a chain along b.     

Synthesis of Methyl (20R,22E)‐ and (20S,22E)‐3‐Oxochola‐1,4,22‐ trien‐24‐oate

Methyl (22E)‐3‐oxochola‐1,4,22‐trien‐24‐oate ( 4 ; C₂₅H₃₄O₃) is a naturally occurring steroid with unknown configuration at C(20). Starting from the (20S)‐3‐oxo‐23,24‐dinorchol‐4‐en‐22‐al ( 1a ), we prepared both diastereoisomeric methyl esters 4a and 4b by a three‐step procedure (Scheme). In the case of 4b , the initial epimerization of aldehyde 1a was followed by completion of the sequence and then separation via fractional crystallization to afford pure (20R)‐methyl ester 4a and its (20S)‐diastereomer 4b . Only the analytical data of the (20S)‐compound 4b were in good agreement with those reported for the natural product.     

Isomerization of (all‐E)‐Cucurbitaxanthin A

Cucurbitaxanthin A (=(all‐E,3S,5R,6R,3′R)‐3,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐5,3′‐diol; 1 ) was submitted to thermal isomerization and to I₂‐catalysed photoisomerization. The structure of the main reaction products (9Z)‐ ( 2 ), (9′Z)‐ ( 3 ), (13Z)‐ ( 4 ), and (13′Z)‐cucurbitaxanthin A ( 5 ) was determined by their UV/VIS, CD, ¹H‐NMR, and mass spectra.     

Kinetic study of the gas‐phase photolysis and OH radical reaction of E,Z‐ and E,E‐2,4‐Hexadienedial

Unsaturated 1,6‐dicarbonyls like 2,4‐hexadienedial are ring opening products in the OH initiated photo‐oxidation of aromatic hydrocarbons. In the present study, the photolysis of E,Z‐ and E,E‐2,4‐hexadienedial has been investigated under natural sunlight conditions in a large volume outdoor reaction chamber. In the case of the E,Z‐isomer, an extremely rapid isomerization into the E,E‐form was observed. The photoisomerization frequency, relative to that of NO₂, was found to be J(E,Z‐2,4‐hexadienedial)/J(NO₂) = (0.148 ± 0.012). A more complex photolysis behavior was observed for E,E‐2,4‐hexadienedial. Here, a fast equilibrium preceded a comparably slow photolysis. For the equilibrium reaction, relative frequencies of J(E,E‐2,4‐hexadienedial → EQUI)/J(NO₂) = (0.113 ± 0.009) and J(EQUI → E,E‐2,4‐hexadienedial)/J(NO₂) = (0.192 ± 0.016) were obtained, giving an equilibrium constant of K = (0.59 ± 0.07). For the photolysis frequencies, ratios of J(E,E‐2,4‐hexadienedial → products)/J(NO₂) = J(EQUI → products)/J(NO₂) = (1.22 ± 0.45)·10⁻² were determined. Qualitative aerosol measurements during the experiments showed that the photolysis of 2,4‐hexadienedials is a source of secondary organic aerosol. In addition to the photolysis study, OH radical reaction rate constants were determined, values of (7.4 ± 1.9)·10⁻¹¹ and (7.6 ± 0.8)·10⁻¹¹ cm³ s⁻¹ were obtained for E,Z‐ and E,E‐2,4‐hexadienedial, respectively. The results indicate that the dominant fate of E,Z‐2,4‐hexadienedial in the atmosphere will be photoisomerization, while for E,E‐2,4‐hexadienedial, both photolysis and OH radical reaction will be important sinks. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 689–697, 1999     

(E,E)‐2,5‐Di­methoxy‐1,4‐bis­[2‐(3,4,5‐tri­methoxy­phenyl)­ethenyl]­benzene

In the title compound, C₃₀H₃₄O₈, molecular symmetry is coincident with crystallographic inversion symmetry. A three‐dimensional network is generated containing both C—H·π and C—H·n(O) interactions. A comparison of the geometry of this mol­ecule and the structure of a number of 2,4,6‐tri­methoxy‐substituted analogues is provided.     

(E)‐N′‐(4‐Chlorobenzylidene)‐, (E)‐N′‐(4‐bromobenzylidene)‐ and (E)‐N′‐[4‐(diethylamino)benzylidene]‐ derivatives of 4‐hydroxybenzohydrazide

The 4‐chloro‐ [C₁₄H₁₁ClN₂O₂, (I)], 4‐bromo‐ [C₁₄H₁₀BrN₂O₂, (II)] and 4‐diethylamino‐ [C₁₈H₂₁N₃O₂, (III)] derivatives of benzylidene‐4‐hydroxybenzohydrazide, all crystallize in the same space group (P2₁/c), (I) and (II) also being isomorphous. In all three compounds, the conformation about the C=N bond is E. The molecules of (I) and (II) are relatively planar, with dihedral angles between the two benzene rings of 5.75 (12) and 9.81 (17)°, respectively. In (III), however, the same angle is 77.27 (9)°. In the crystal structures of (I) and (II), two‐dimensional slab‐like networks extending in the a and c directions are formed via N—H...O and O—H...O hydrogen bonds. The molecules stack head‐to‐tail viaπ–π interactions involving the aromatic rings [centroid–centroid distance = 3.7622 (14) Å in (I) and 3.8021 (19) Å in (II)]. In (III), undulating two‐dimensional networks extending in the b and c directions are formed via N—H...O and O—H...O hydrogen bonds. The molecules stack head‐to‐head viaπ–π interactions involving inversion‐related benzene rings [centroid–centroid distances = 3.6977 (12) and 3.8368 (11) Å].