Heterocyclic rearrangements. N,N-diphenylhydrazones,oximes and O-methyloximes of 3-benzoyl-5-phenyl-1,2,4-oxadiazole

The behaviour of (E)- and (Z)-N,N-diphenylhydrazones and O-Methyloximes of 3-benzoyl-5-phenyl-1,2,4-oxadiazole has been studied. When refluxed in benzene, or in dioxane-water (1:1), the (Z)-N,N-diphenylhydrazone 8Z gave the indazole 11 or the substituted semicarbazide 12 , respectively. The O-methyloxime 14Z did not give any rearrangement. A criticism of the oximation reaction of 3-benzoyl-5-phenyl-1,2,4-oxadiazole is also reported.     

ELECTROCHEMICAL ISOMERIZATION OF SULFINE

Abstract

Electrochemical isomerization of 1-phenyl-2, 2-dimethylpropane-1-thione S-oxide (phenyl-t-butylsulfine, E and Z form, 1a and 1b) was studied. Anodic isomerization of 1a gave the two isomers of the sulfine only, but cathodic reductive isomerization of 1a gave pivalophenone and 1-cyano-2-phenyl-3, 3-dimethyl-1-butene in addition to the E and Z isomers. This is the first example of an electrochemical reaction of a sulfine.     

(all-E)-12′-Apozeaxanthinol,Persicaxanthine und Persicachrome

( all-E)-12′-Apozeanthinol, Persicaxanthine, and Persicachromes Reexamination of the so-called ‘persicaxanthins’ and ‘persicachromes’, the fluorescent and polar C₂₅-apocarotenols from the flesh of cling peaches, led to the identification of the following components: (3R)-12′-apo-β-carotene-3,12′-diol ( 3 ), (3S,5R,8R, all-E)- and (3S,5R,8S,all-E)-5,8-epoxy-5,8-dihydro-12′-apo-β-carotene-3,12′-diols (4 and 5, resp.), (3S,5R,6S,all-E)-5,6-epoxy-5,6-dihydro-l2′-apo-β-carotene-3,12′-diol =persicaxanthin; ( 6 ), (3S,5R,6S,9Z,13′Z)-5,6-dihydro-12′apo-β-carotene-3,12′-diol ( 7 ; probable structure), (3S,5R,6S,15Z)-5,6-epoxy-5,6-dihydro-12′-apo-β-carotene-3,12′-diol ( 8 ), and (3S,5R,6S,13Z)-5,6-epoxy-5,6-dihydro-12′-apo-β-carotene-3,12′-diol ( 9 ). The (Z)-isomers 7 – 9 are very labile and, after HPLC separation, isomerized predominantly to the (all-E)-isomer 6 .     

Azimine IV. Kinetik und Mechanismus der thermischen Stereoisomerisierung von 2,3-Diaryl-1-phthalimido-aziminen

Azimines IV. Kinetics and Mechanism of the Thermal Stereoisomerization of 2,3-Diaryl-1-phthalimido-azimines¹) Mixtures of (1E, 2Z)- and (1Z, 2E)-2-phenyl-1-phthalimido-3-p-tolyl-azimine ( 3a and 3b , resp.) and (1E, 2Z)- and (1Z, 2E)-3-phenyl-1-phthalimido-2-p-tolylazimine ( 4a and 4b , resp.) were obtained by the addition of oxidatively generated phthalimido-nitrene (6) to (E)- and (Z)-4-methyl-azobenzene ( 7a and 7b , resp.). Whereas complete separation of the 4 isomers 3a, 3b, 4a and 4b was not possible, partial separation by chromatography and crystallization led to 5 differently composed mixtures of azimine isomers. The spectroscopic properties of these mixtures (UV., ¹H-NMR.) were used to determine the ratios of isomers in the mixtures, and served as a tool for the assignment of constitution and configuration to those isomers which were dominant in each of these mixtures, respectively. Investigation of the isomerization of the azimines 3a, 3b, 4a and 4b within the 5 mixtures at various concentrations by ¹H-NMR.-spectroscopy at room temperature revealed that only stereoisomers are interconverted ( 3a ? 3b; 4a ? 4b) and that the (1E, 2Z) ? (1Z, 2E) stereoisomerization is a unimolecular reaction. These observations exclude an isomerization mechanism via an intermediate 1-phthalimido-triaziridine (2) or via dimerization of 1-phthalimido-azimines (1) , respectively. The 3-p-tolyl substituted stereoisomers 3a and 3b isomerized slightly slower than the 3-phenyl substituted ones 4a and 4b , an effect which is consistent with the assumption that the rate determining step of the interconversion of (1E, 2Z)- and (1Z, 2E)-1-phthalimido-azimines (1a ? 1b) is the stereoisomerization of the stereogenic center at N(2), N(3), either by inversion of N(3) or by rotation around the N(2), N(3) bond. The total isomerization process is assumed to occur via the thermodynamically less stable (1Z, 2Z)- and (1E, 2E)-isomers 1c and 1d , respectively, as intermediates in undetectably low concentrations which stay in rapidly established equilibria with the observed, thermodynamically more stable (1E, 2Z)- and (1Z, 2E)-isomers 1a and 1b , respectively. At higher temperatures, the azimines 3 and 4 are transformed into N-phenyl-N,N′-phthaloyl-N′-p-tolyl-hydrazine (8) with loss of nitrogen.     

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.     

New Results in Homoheptalene Chemistry

The thermal reaction of homoazulene (=bicyclo[5.3.1]undeca‐1,3,5,7,9‐pentaene; 2 ) with dimethyl acetylenedicarboxylate (ADM) in 1,2‐dichloroethane (ClCH₂CH₂Cl) results, in contrast to an earlier report [5], in formation of not only dimethyl homoheptalene‐4,5‐dicarboxylate (=bicyclo[5.5.1]trideca‐1,3,5,7,9,11‐hexaene‐4,5‐dicarboxylate; 3 ), but also of a 4 : 1 mixture of 3 and dimethyl homoheptalene‐2,3‐dicarboxylate ( 13 ) in almost quantitative yield (Schemes 1 and 3). The structures of both homoheptalenes have been corroborated by X‐ray crystal‐structure analysis (Fig. 5). The double‐bond‐shifted (DBS) isomers 3 ′ and 13 ′ of 3 and 13 , respectively, could not be detected in their ¹H‐NMR spectra (600 MHz threshold of detection ≥0.5%), in agreement with the AM1‐calculated ΔH values of the four isomeric homoheptalene‐dicarboxylates (cf. Table 4). Vilsmeyer formylation of homoazulene ( 2 ) gave homoazulene‐8‐carbaldehyde ( 14 ) in a yield of 67%, which, on treatment with benzylidene‐(triphenyl)‐λ⁵‐phosphane, gave, in almost quantitative yield, a 1.6 : 1 mixture of (Z)‐ and (E)‐8‐styrylhomoazulene ((Z)‐ 15 and (E)‐ 15 , resp.). Thermal reaction of the latter mixture with ADM in 1,2‐dichloroethane led, in a yield of 42%, to a 5 : 1 mixture of dimethyl (Z)‐ and (E)‐2‐styrylhomoheptalene‐4,5‐dicarboxylate ((Z)‐ 15 and (E)‐ 16 , resp.). Both isomers were separated by column chromatography on silica gel. Again, the DBS isomers of (Z)‐ 16 and (E)‐ 16 , i.e., (Z)‐ 16 ′ and (E)‐ 16 ′, could not be detected in the ¹H‐NMR spectra (600 MHz) of pure (Z)‐ 16 and (E)‐ 16 .     

(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.     

The synthesis of pyrazolo[1,2-a]pyrazoles. Regio- and stereo-selective 1,3-dipolar cycloadditions of (1Z)-rel-(4R,5R)-1-arylmethylene-4-benzoylamino-5-phenyl-3-pyrazolidinon-1 -azomethinimines

Reaction of rel-(4R,5R)-4-benzoylamino-5-phenyl-3-pyrazolidinone (4) with aromatic aldehydes 5a-f gave the corresponding (1Z)-rel-(4R,5R)-1-arylmethylene-4-benzoylamino-5-phenyl-3-pyrazolidinon-1-azomethinimines 6a-f . 1,3-Dipolar cycloadditions of azomethinimines 6a-f to various dipolarophiles, which were found to proceed regio- and stereo-selectively, afforded the corresponding pyrazolo[1,2-a]-pyrazoles 8a-f, 10 , and 13–16 . Reaction of azomethinimine 6a with hydrogen cyanide gave rel-(5R,6R)-6-benzoylamino-5,6-dihydro-3,5-diphenyl-1-oxo-1H,7H-pyrazolo[1,2-a][1,2,3]triazole (18) as a representative of a new ring system.     

Stereoselective Synthesis of Vinylboronates by Rh‐Catalyzed Borylation of Stereoisomeric Mixtures

The stereoselective preparation of vinylboronates via rhodium‐catalyzed borylation of E/Z mixtures of vinyl actetates is described, and this method was also extended to synthesis of vinyldiboronates. These transformations feature high functional group compatibility and mild reaction conditions. Control experiments support a mechanism that involved a Rh‐catalyzed borylation‐isomerization sequence. The isomerization of (Z)‐vinylboronates to (E)‐isomers was also demonstrated.     

Additive Pummerer reactions of vinylic sulfoxides. Synthesis of γ-hydroxy-α,β-unsaturated esters, α-hydroxyketones, and 2-phenylsulfenyl aldehydes and primary alcohols

Treatment of β-monosubstituted vinylic sulfoxides 1 with trifluoroacetic anhydride in dichloromethane gave excellent yields of 1,2-bis(trifluoroacetoxy)thioethers 6. Mildly basic methanolysis of 2-alkyl-substituted 6 gave α-hydroxyaldehydes 11 as monomer-dimer mixtures; similar treatment of the 2-aryl analogues afforded aryl (hydroxymethyl) ketones 12. Compounds 11 underwent Wittig reactions with methoxycarbonylmethylenetriphenylphosphorane to give high yields of γ-hydroxy-α,β-unsaturated esters 13, predominantly as the E-isomers. β-Monosubstituted vinylic sulfoxides 1 possessing a β-aryl group, and β-disubstituted vinylic sulfoxides 3 reacted with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride to give 2-(phenylsulfenyl)acylals 14. These gave 2-phenylsulfenyl aldehydes 15 upon basic methanolysis, and the corresponding primary alcohols 16 on reduction with sodium borohydride. Reaction of both geometric isomers of enantiomerically pure vinylic sulfoxide 1o with TFAA gave racemic 6o as a mixture of diastereomers. Reaction of optically pure (E)- and (Z)-1p with trifluoromethanesulfonic anhydride-sodium acetate in acetic anhydride gave acylal 19 in 10.5 and 23% e.e., respectively.     

Azimine. V.. Untersuchungen zur stereoisomerie an der N(2), N(3)-bindung von 2, 3-dialkyl-1-phthalimido-aziminen

Azimines. V. Investigation on the Stereoisomerism Around the N (2), N (3) Bond in 2, 3-Dialkyl-1-phthalimido-azimines 2, 3-(cis-1, 3-Cyclopentylene)-1-phthalimido-azimine ( 7 ) and isomerically pure (2 Z)- and (2 E)-2, 3-diisopropyl-1-phthalimido-azimine ( 9a and 9b ) were prepared by the addition of phthalimido-nitrene ( 1 ) to 2, 3-diazabicyclo [2.2.1]hept-2-ene ( 6 ) and to (E)- and (Z)-1, 1′-dimethylazoethane ( 8a and 8b ), respectively. Comparison of their UV. spectra with those of two stereoisomeric azimines of known configuration, namely (1 E, 2 Z)- and (1 Z, 2 E)-2, 3-dimethyl-1-phthalimido-azimine ( 5a and 5b ), reveals that 2, 3-dialkyl-1-phthalimido-azimines with (2 Z)-configuration are characterized by a shoulder at about 258 nm (? ≈? 14,000) and those with (2 E)-configuration by a maximum at 270–278 nm (? ≈? 10,000). The (2 E)-azimine 9b isomerizes under acid catalysis as well as thermally and photochemically into the more stable (2 Z)-isomer 9a . Under the last two conditions the isomerization is accompanied by a slower fragmentation with loss of nitrogen into N, N′-diisopropyl-N, N′-phthaloylhydrazine ( 4 , R = iso-C₃H₇). The same fragmentation was also observed on thermolysis and photolysis of the (2 Z)-isomer 9a . The kinetic parameters for the thermal isomerization of 9b (they fit first-order plots) and for the fragmentation of 9a and 9b were determined by ¹H-NMR. spectroscopy in benzene, trichloromethane and acetonitrile. In the photolysis of 9a or 9b the fragmentation is accompanied by dissociation into the azo compounds 8a or 8b and the nitrene 1 , the latter being subject to trapping by cyclohexene. With the azimine 7 , an analogous thermal fragmentation was observed to give N, N′-(cis-1, 3-cyclo-pentylene)-N, N′-phthaloylhydrazine ( 15 ), but more energetic conditions were required than with 9 . Photolysis of 7 led exclusively to dissociation into the azo compound 6 and the nitrene 1 , perhaps because the fragmentation of 7 is prevented by ring strain.     

Photochemical reactions. 134th Communication. Photochemistry of 5,6-epoxy-5,6-dihydro-3,4-methano-β-ionone: Influence of a cyclopropane ring on the reactivity of an ylide intermediate

On ¹n,π*-excitation(λ > 347 nm), the diastereomeric methanoepoxyenones (E)- 6 undergo isomerization via C,O-cleavage of the oxirane leading to diastereomeric photoproducts ((E)- 5 →(E/Z)- 13 and 14 ; (E)- 6 →(E/Z)- 16 and 17 ). On ¹π,π*-excitation (λ = 254 nm) of either (E)- 5 ) or (E- 6 the photoproducts 9, 10 and 11 are formed. By laser flash photolysis (λ = 265 nm) the ylide intermediate 3 was detected, with a lifetime of 10 μs in MeCN at ambient temperature. Stern-Volmer analysis of the ylide quenching by MeOH disclosed that compounds 9 and 10 , but not 11 , arise from the ylide intermediate e .     

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).     

Two isomeric fourteen-membered bis-dithioacetals derived from (<Emphasis Type="Italic">Z</Emphasis>)- and (<Emphasis Type="Italic">E</Emphasis>)-but-2-ene-1,4-dithiols

(Z)-But-2-ene-1,4-dithiol was found to undergo isomerization into the E isomer. Condensation of (Z)- and (E)-but-2-ene-1,4-dithiols with acetaldehyde gave isomeric fourteen-membered bis-dithioacetals whose structure was determined by X-ray analysis.     

Recent Advances in the Z/E Isomers of Tetraphenylethene Derivatives: Stereoselective Synthesis,AIE Mechanism,Photophysical Properties,and Application as Chemical Probes

Focused research on the Z/E isomers of tetraphenylethene (TPE) derivatives is scarce in comparison with the thousands of luminogens with AIE properties (AIEgens) that have been synthesized based on the TPE moiety. The similar chemical and physical properties of the Z/E isomers make them difficult to separate by using conventional chromatographic techniques. However, they can be isolated by introducing polar groups and the pure isomers exhibit very different photophysical properties, mechanochromism, and host–guest coordination, as well as assisting in deciphering the AIE mechanism. In this Minireview, we present an overview of the disagreement regarding the AIE mechanism between the restriction of intramolecular vibration and photoinduced Z/E isomerization. Then, we discuss the development of (Z)‐/(E)‐TPE derivatives, their use in host–guest detection, and their mechanoluminescence properties, with a focus on their photophysical characteristics. Finally, we explore the stereoselective synthesis of pure (Z)‐/(E)‐TPE derivatives.     

Synthesis of 4-β-D-arabinofuranosyl-5,6-dihydro-2H-1,2,4-thiadiazin-3-one 1,1-dioxide and x-ray diffraction analysis of its 2′,3-anhydro precursor

Reaction of 2-amino-3′,5′-bis(O-tert-butyldimethylsilyl)-β- D -arabinofuran[1′,2′:4,5]-2-oxazoline with 2-chloroethylsulfonyl chloride in the presence of sodium bicarbonate followed by removal of the protecting groups gave 2′,3-anhydro-4-β- D -arabinofuranosyl-5,6-dihydro-2H-1,2,4-thiadiazin-3-one 1,1-dioxide ( 5 ), which by treatment with ammonia was converted to 4-β- D -arabinofuranosyl-5,6-dihydro-2H-1,2,4-thiadiazin-3-one 1,1-dioxide ( 6 ). The structure of compound 5 was unequivocally established by means of an x-ray diffraction analysis. The compound crystallized in the space group P2₁2₁2₁ with unit cell dimensions a = 5.883(3), b = 9.352(2), c = 18.769(7) Å, Z = 4. Its structure was established by direct multisolution techniques and refined by the full matrix least squares method to a final R value of 0.058 for the 1515 reflections observed.     

Nouveaux types de sucres acétyléniques. Communication préliminaire

Novel types of acetylenic sugars The coupling, following Cadiot's procedure, of a 6-bromo-5,6-dideoxy-1,2-O-isopropylidène-3-O-methyl-α-D -xylo-hex-5-yno-1, 4-furanose (1) with phenylacetylene, 2-propyn-1-ol or terminal acetylenic sugars gave with excellent yields the expected diynes (an enediyne when the terminal acetylene was the 3,5, 6-trideoxy-1,2-O-isopropylidene-α-D -glycero-hex-3-en-5-yno-1,4-furanose 7 ). The chloro analogue 8 of 1 on treatment with lithium thiophenate gave the corresponding phenylthio-acetylenic sugar 9 . An acetylene was also formed by reacting the gem-difluoro-olefinic sugar 10 with butyllithium whereas the same olefinic sugar and its 3-O-benzyl analogue 11 gave only a gem-fluoro-arylthio-olefinic sugar (13–15) as a mixture of the Z and E isomers (Z/E > 4) when treated with the conjugate base of an arylmercaptan.     

Reaction of sulfene with heterocyclic N,N-disubstituted α-aminomethvlene ketones V. Synthesis of 1,2-oxatliiino[5.6-c] pyridine and 1,2-oxathiino[5,6-c] quinoline derivatives

Reaction of sulfene with N,N-disubstituted 3-aminomethylene-1-(methyl, methylphenyl, phenyl)-4-piprridones and 3-aminomethylene-2,3-dihydro-1-plumy 1–4(1H) quinolones gave N,N-disubstituted 4-amino-3,4,5,6,7.8-hexahydro-6-(methyl, methylphenyl, phenyl)-1,2-oxathiino-[5,6-c] pyridine 2,2-dioxides and 4-amino-6-phenyl-3,4,5,6-tetrahydro-1,2-oxathiino[5,6-c]quinoline 2,2-dioxides, respectively, whereas N,N-disubstituted 3-aminomethylene-2,3-dihydro-1-methyl-4(1H) quinolones did not react. Slow air oxidation in the cold of intermediates 2,3-dihydro-3-hydroymethyIene-1-(methyl, phenyl)-4(1H) quinolones gave the corresponding 1-substituted 1,4-dihydro-4-oxo-3-quinolinecarboxyaldehydes.     

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.     

Synthesis and characterization of macrocyclic ligands containing benzene and/or pyridine rings and their nickel(II), copper(II) and zinc(II) complexes

Macrocycles, 7,16-diethyl-5,6,7,8,9,14,15,16,17,18-decahydrodibenzo[b,i][1,4,8,11]tetraazacyclotetradecine ( 2B ), 7,16-diethyl-5,6,7,8,9,14,15,16,17,18-decahydro-(E)dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine ( 2E ) and 7,16-diethyl-5,6,7,8,9,14,15,16,17,18-decahydro-(Z)-dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine ( 2Z ), have been synthesized by hydrogenation of 7,16-diethyl-5,14-dihydrodibenzo[b,i][1,4,8,11]tetraazacyclotetradecine and 7,16-diethyl-5,14-dihydro-(E)- or -(Z)-dipyrido[b,i][1,4,8,11]tetraazacyclotetradecine. In each case, two isomers were produced with differing orientations of the ethyl groups relative to the macrocyclic plane. The isomers were separated by repeated recrystallization. Carbon-13 nmr spectra for the metal-free ligands were used to distinguish between the two isomers. The nickel(II), copper(II) and zinc(II) complexes of the two isomers of 2B were prepared and their spectroscopic data were determined. The ligand-field bands in the 15000–30000 cm^?1 region for the nickel(II) and copper(II) complexes are consistent with square-planar configurations. A strong band appearing at ca. 3200 cm^?1 in the infrared spectra was assigned to the N-H stretching mode which shifted to lower frequency upon metal coordination.