(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.     

(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.     

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.     

Four (E,Z,E)‐1‐(4‐alkoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐trienes

The crystal structures of the four E,Z,E isomers of 1‐(4‐alk­oxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, namely (E,Z,E)‐1‐(4‐methoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₁₉H₁₇NO₃, (E,Z,E)‐1‐(4‐ethoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₂₀H₁₉NO₃, (E,Z,E)‐1‐(4‐nitro­phen­yl)‐6‐(4‐n‐propoxyphen­yl)hexa‐1,3,5‐triene, C₂₁H₂₁NO₃, and (E,Z,E)‐1‐(4‐n‐butoxy­phen­yl)‐6‐(4‐nitro­phen­yl)hexa‐1,3,5‐triene, C₂₂H₂₃NO₃, have been determined. Inter­molecular N⋯O dipole inter­actions between the nitro groups are observed for the meth­oxy derivative, while for the eth­oxy derivative, two adjacent mol­ecules are linked at both ends through N⋯O dipole–dipole inter­actions between the N atom of the nitro group and the O atom of the eth­oxy group to form a supra­molecular ring‐like structure. In the crystal structures of the n‐prop­oxy and n‐but­oxy derivatives, the shortest inter­molecular distances are those between the two O atoms of the alk­oxy groups. Thus, the nearest two mol­ecules form an S‐shaped supra­molecular dimer in these crystal structures.     

Confirmation of the Absolute (3R,3′S,6′R)‐Configuration of (all‐E)‐3′‐Epilutein

Circular dichroism (CD) spectroscopy was used to distinguish between the isomeric (all‐E)‐configured 3′‐epilutein ( 2 ) and 6′‐epilutein ( 8 ) to establish the absolute configuration of epilutein samples of different (natural and semisynthetic) origin, including samples of 2 obtained from thermally processed sorrel. Thus, the CD data of lutein ( 1 ) and epilutein samples ( 2 ) were compared. Our results unambiguously confirmed the (3R,3′S,6′R)‐configuration of all epilutein samples. Compound 2 was thoroughly characterized, and its ¹³C‐NMR data are published herewith for the first time.     

(E)‐1‐(2′‐Deoxy‐β‐d‐ribo­furan­osyl)‐2,4‐di­fluoro‐5‐(2‐iodo­vinyl)­benzene

This analysis of the title compound, C₁₃H₁₃F₂IO₃, establishes the orientation of (E)‐5‐(CH=CH—I) as antiperiplanar (ap) to the C—C bond (5–6 position) of the 2,4‐di­fluoro­phenyl ring system, with the (E)‐5‐(CH=CH—I) H atom located in close proximity (2.17 Å) to the F4 atom of the 2,4‐di­fluoro­phenyl moiety.     

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.     

(E/Z)‐Isomerization of 3′‐Epilutein

3′‐Epilutein (=(all‐E,3R,3′S,6′R)‐4′,5′‐didehydro‐5′,6′‐dihydro‐β,β‐carotene‐3,3′‐diol; 1 ), isolated from the flowers of Caltha palustris, was submitted to both thermal isomerization and I₂‐catalyzed photoisomerization. The structures of the main products (9Z)‐ 1 , (9′Z)‐ 1 , (13Z)‐ 1 , (13′Z)‐ 1 , (15Z)‐ 1 , and (9Z,9′Z)‐ 1 were determined based on UV/VIS, CD, ¹H‐NMR, and MS data.     

Reactions of Methyl Diazoacetate with (E)‐ and (Z)‐1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: Novel and Unanticipated Pathways

The cycloadditions of methyl diazoacetate to 2,3‐bis(trifluoromethyl)fumaronitrile ((E)‐ BTE ) and 2,3‐bis(trifluoromethyl)maleonitrile ((Z)‐ BTE ) furnish the 4,5‐dihydro‐1H‐pyrazoles 13 . The retention of dipolarophile configuration proceeds for (E)‐ BTE with > 99.93% and for (Z)‐ BTE with > 99.8% (CDCl₃, 25°), suggesting concertedness. Base catalysis (1,4‐diazabicyclo[2.2.2]octane (DABCO), proton sponge) converts the cycloadducts, trans‐ 13 and cis‐ 13 , to a 94 : 6 equilibrium mixture (CDCl₃, r.t.); the first step is N‐deprotonation, since reaction with methyl fluorosulfonate affords the 4,5‐dihydro‐1‐methyl‐1H‐pyrazoles. Competing with the cis/trans isomerization of 13 is the formation of a bis(dehydrofluoro) dimer (two diastereoisomers), the structure of which was elucidated by IR, ¹⁹F‐NMR, and ¹³C‐NMR spectroscopy. The reaction slows when DABCO is bound by HF, but F^? as base keeps the conversion to 22 going and binds HF. The diazo group in 22 suggests a common intermediate for cis/trans isomerization of 13 and conversion to 22 : reversible ring opening of N‐deprotonated 13 provides 18 , a derivative of methyl diazoacetate with a carbanionic substituent. Mechanistic comparison with the reaction of diazomethane and dimethyl 2,3‐dicyanofumarate, a related tetra‐acceptor‐ethylene, brings to light unanticipated divergencies.     

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.     

Conformations of the Nine‐Membered Ring in the B‐Nor‐5,10‐secosteroids. X‐Ray and NMR Analysis

The conformations of (Z)‐ and (E)‐5‐oxo‐B‐nor‐5,10‐secocholest‐1(10)‐en‐3β‐yl acetates ( 2 and 3 , resp.) were examined by a combination of X‐ray crystallographic analysis and NMR spectroscopy, with emphasis on the geometry of the cyclononenone moiety. The ¹H‐ and ¹³C‐NMR spectra showed that the unsaturated nine‐membered ring of (E)‐isomer 3 in C₆D₆ and (D₆)acetone solution exists in a sole conformation of type B ₁ , which is similar to its solid‐state conformation. The (Z)‐isomer 2 in C₆D₆, CDCl₃, and (D₆)acetone solution, however, exists in two conformational forms of different families, with different orientation of the carbonyl group, the predominant form (85%) corresponding to the conformation of type A ₁ and the minor (15%) to the conformation A ₂ present also in the crystalline state. In this solid‐state conformations of the nine‐membered ring of both compounds, the 19‐Me and 5‐oxo groups are ‘β’‐oriented. The NMR analysis suggests that the nine‐membered ring of 4 has a conformation of type C ₁ in CDCl₃ solution.     

(E)‐(4‐Hydroxyphenyl)(4‐nitrophenyl)diazene, (E)‐(4‐methoxyphenyl)(4‐nitrophenyl)diazene and (E)‐[4‐(6‐bromohexyloxy)phenyl](4‐cyanophenyl)diazene

Syntheses and X‐ray structural investigations have been carried out for (E)‐(4‐hydroxy­phenyl)(4‐nitro­phenyl)­diazene, C₁₂H₉N₃O₃, (Ia), (E)‐(4‐methoxy­phenyl)(4‐nitro­phenyl)­diazene, C₁₃H₁₁N₃O₃, (IIIa), and (E)‐[4‐(6‐bromo­hexyl­oxy)­phenyl](4‐cyano­phenyl)­diazene, C₁₉H₂₀BrN₃O, (IIIc). In all of these compounds, the mol­ecules are almost planar and the azo­benzene core has a trans geometry. Compound (Ia) contains four and compound (IIIc) contains two independent mol­ecules in the asymmetric unit, both in space group P (No. 2). In compound (Ia), the independent mol­ecules are almost identical, whereas in crystal (IIIc), the two independent mol­ecules differ significantly due to different conformations of the alkyl tails. In the crystals of (Ia) and (IIIa), the mol­ecules are arranged in almost planar sheets. In the crystal of (IIIc), the mol­ecules are packed with a marked separation of the azo­benzene cores and alkyl tails, which is common for the solid crystalline precursors of mesogens.     

Stereo‐Inversion in the (4R)‐γ‐Decanolactone Synthesis by Saccharomyces cerevisiae: (2E,4S)‐4‐Hydroxydec‐2‐enoic Acid Acts as a Key Intermediate

Methyl (2E,4R)‐4‐hydroxydec‐2‐enoate, methyl (2E,4S)‐4‐hydroxydec‐2‐enoate, and ethyl (±)‐(2E)‐4‐hydroxy[4‐²H]dec‐2‐enoate were chemically synthesized and incubated in the yeast Saccharomyces cerevisiae. Initial C‐chain elongation of these substrates to C₁₂ and, to a lesser extent, C₁₄ fatty acids was observed, followed by γ‐decanolactone formation. Metabolic conversion of methyl (2E,4R)‐4‐hydroxydec‐2‐enoate and methyl (2E,4S)‐4‐hydroxydec‐2‐enoate both led to (4R)‐γ‐decanolactone with >99% ee and 80% ee, respectively. Biotransformation of ethyl (±)‐(2E)‐4‐hydroxy(4‐²H)dec‐2‐enoate yielded (4R)‐γ‐[²H]decanolactone with 61% of the ²H label maintained and in 90% ee indicating a stereoinversion pathway. Electron‐impact mass spectrometry analysis (Fig. 4) of 4‐hydroxydecanoic acid indicated a partial C(4)→C(2) ²H shift. The formation of erythro‐3,4‐dihydroxydecanoic acid and erythro‐3‐hydroxy‐γ‐decanolactone from methyl (2E,4S)‐4‐hydroxydec‐2‐enoate supports a net inversion to (4R)‐γ‐decanolactone via 4‐oxodecanoic acid. As postulated in a previous work, (2E,4S)‐4‐hydroxydec‐2‐enoic acid was shown to be a key intermediate during (4R)‐γ‐decanolactone formation via degradation of (3S,4S)‐dihydroxy fatty acids and precursors by Saccharomyces cerevisiae.     

Multiple Pentafluorophenylation of 2,2,3,3,5,6,6‐Heptafluoro‐3,6‐dihydro‐2H‐1,4‐oxazine with an Organosilicon Reagent: NMR and DFT Structural Analysis of Oligo(perfluoroaryl) Compounds

The reagent Me₃Si(C₆F₅) was used for the preparation of a series of perfluorinated, pentafluorophenyl‐substituted 3,6‐dihydro‐2H‐1,4‐oxazines ( 2 – 8 ), which, otherwise, would be very difficult to synthesize. Multiple pentafluorophenylation occurred not only on the heterocyclic ring of the starting compound 1 (Scheme), but also in para position of the introduced C₆F₅ substituent(s) leading to compounds with one to three nonafluorobiphenyl (C₁₂F₉) substituents. While the tris(pentafluorophenyl)‐substituted compound 3 could be isolated as the sole product by stoichiometric control of the reagent, the higher‐substituted compounds 5 – 8 could only be obtained as mixtures. The structures of the oligo(perfluoroaryl) compounds were confirmed by ¹⁹F‐ and ¹³C‐NMR, MS, and/or X‐ray crystallography. DFT simulations of the ¹⁹F‐ and ¹³C‐NMR chemical shifts were performed at the B3LYP‐GIAO/6‐31++G(d,p) level for geometries optimized by the B3LYP/6‐31G(d) level, a technique that proved to be very useful to accomplish full NMR assignment of these complex products.     

ss‐NMR and single‐crystal X‐ray diffraction in the elucidation of a new polymorph of bischalcone (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one

We report a new polymorph of (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one, C₁₇H₁₂F₂O. Contrary to the precedent literature polymorph with Z′ = 3, our polymorph has one half molecule in the asymmetric unit disordered over two 50% occupancy sites. Each site corresponds to one conformation around the single bond vicinal to the carbonyl group (so‐called anti or syn). The other half of the bischalcone is generated by twofold rotation symmetry, giving rise to two half‐occupied and overlapping molecules presenting both anti and syn conformations in their open chain. Such a disorder allows for distinct patterns of intermolecular C—H…O contacts involving the carbonyl and anti‐oriented β‐C—H groups, which is reflected in three ¹³C NMR chemical shifts for the carbonyl C atom. Here, we have also assessed the cytotoxicity of three symmetric bischalcones through their in vitro antitumour potential against three cancer cell lines. Cytotoxicity assays revealed that this biological property increases as halogen electronegativity increases.     

Syntheses and Spectroscopic Study of Some New N‐4‐Fluorobenzoyl Phosphoric Triamides; Crystal Structures of 4‐F‐C6H4C(O)N(H)P(O)R2, R = NH‐C(CH3)3, NH‐CH2C6H5, N(CH3)(CH2C6H5)

Some new N‐4‐Fluorobenzoyl phosphoric triamides with formula 4‐F‐C₆H₄C(O)N(H)P(O)X₂, X = NH‐C(CH₃)₃ ( 1 ), NH‐CH₂‐CH=CH₂ ( 2 ), NH‐CH₂C₆H₅ ( 3 ), N(CH₃)(C₆H₅) ( 4 ), NH‐CH(CH₃)(C₆H₅) ( 5 ) were synthesized and characterized by ¹H, ¹³C, ³¹P NMR, IR and Mass spectroscopy and elemental analysis. The structures of compounds 1 , 3 and 4 were investigated by X‐ray crystallography. The P=O and C=O bonds in these compounds are anti. Compounds 1 and 3 form one dimensional polymeric chain produced by intra‐ and intermolecular ‐P=O···H‐N‐ hydrogen bonds. Compound 4 forms only a centrosymmetric dimer in the crystalline lattice via two equal ‐P=O···H‐N‐ hydrogen bonds. ¹H and ¹³C NMR spectra show two series of signals for the two amine groups in compound 1 . This is also observed for the two α‐methylbenzylamine groups in 5 due to the presence of chiral carbon atom in molecule. ¹³C NMR spectrum of compound 4 shows that ²J(P,C_aliphatic) coupling constant for CH₂ group is greater than for CH₃ in agreement with our previous study. Mass spectra of compounds 1 ‐ 3 (containing 4‐F‐C₆H₄C(O)N(H)P(O) moiety) indicate the fragments of amidophosphoric acid and 4‐F‐C₆H₄CN⁺ that formed in a pseudo McLafferty rearrangement pathway. Also, the fragments of aliphatic amines have high intensity in mass spectra.     

Preparation and Spectroscopic Characterization of (9Z,9′Z)‐Lutein (Neolutein C)

The preparation of pure, crystalline (9Z,9′Z)‐lutein (neolutein C; 2 ) by I₂‐catalyzed photoisomerization of (all‐E)‐lutein ( 1 ) is described. The structure of 2 was unambiguously determined by UV/VIS, CD, and NMR spectroscopy, as well as by mass spectrometry, and the complete assignment of the ¹³C‐NMR spectrum of this carotenoid is presented for the first time.     

Three structures containing (E)‐1,2‐bis­(benzimidazol‐2‐yl)ethene groups

Two of the title compounds, namely (E)‐1,2‐bis­(1‐methyl­benzimidazol‐2‐yl)ethene, C₁₈H₁₆N₄, (Ib), and (E)‐1,2‐bis­(1‐ethyl­benzimidazol‐2‐yl)ethene, C₂₀H₂₀N₄, (Ic), consist of centrosymmetric trans‐bis­(1‐alkyl­benzimidazol‐2‐yl)ethene mol­ecules, while 3‐eth­yl‐2‐[(E)‐2‐(1‐ethyl­benzimidazol‐2‐yl)­ethen­yl]benzimidazol‐1‐ium perchlorate, C₂₀H₂₁N₄⁺·ClO₄⁻, (II), contains the monoprotonated analogue of compound (Ic). In the three structures, the benzimidazole and benzimidazolium moieties are essentially planar; the geometric parameters for the ethene linkages and their bonds to the aromatic groups are consistent with double and single bonds, respectively, implying little, if any, conjugation of the central C=C bonds with the nitro­gen‐containing rings. The C—N bond lengths in the N=C—N part of the benzimidazole groups differ and are consistent with localized imine C=N and amine C—N linkages in (Ib) and (Ic); in contrast, the corresponding distances in the benzimidazolium cation are equal in (II), consistent with electron delocalization resulting from protonation of the amine N atom. Crystals of (Ib) and (Ic) contain columns of parallel mol­ecules, which are linked by edge‐over‐edge C—H⋯π overlap. The columns are linked to one another by C—H⋯π inter­actions and, in the case of (Ib), C—H⋯N hydrogen bonds. Crystals of (II) contain layers of monocations linked by π–π inter­actions and separated by both perchlorate anions and the protruding eth­yl groups; the cations and anions are linked by N—H⋯O hydrogen bonds.     

A series of substituted (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐ones

In the molecular structures of a series of substituted chalcones, namely (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one, C₂₁H₁₅FO₂, (I), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐fluorophenyl)prop‐2‐en‐1‐one, C₂₁H₁₄F₂O₂, (II), (2E)‐1‐(4‐chlorophenyl)‐3‐(2‐fluoro‐4‐phenoxyphenyl)prop‐2‐en‐1‐one, C₂₁H₁₄ClFO₂, (III), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₂, (IV), and (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methoxyphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₃, (V), the configuration of the keto group with respect to the olefinic double bond is s‐cis. The molecules pack utilizing weak C—H...O and C—H...π intermolecular contacts. Identical packing motifs involving C—H...O interactions, forming both chains and dimers, along with C—H...π dimers and π–π aromatic interactions are observed in the fluoro, chloro and methyl derivatives.     

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).