Diels-Alder Reactions of [2.2] Paracyclophan-1-ene and [2.2] Paracyclophane-1,9-diene with 3,6-Disubstituted 1,2,4,5-Tetrazines

[2.2] Paracyclophan-1-ene ( 1 ) and [2.2] paracyclophane-1,9-diene ( 6 ) apparently act as dienophiles with inverse electron demand and smoothly react with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate ( 2a ) at room temperature forming dihydropyridazine adducts, which are dehydrogenated to the pyridazino-anellated [2.2] paracyclophanes 5a and 8a , respectively. The molecular structure of 5a is determined by X-ray crystal-structure analysis. Under more rigorous conditions, phenyl-substituted derivatives 5b and 8b are obtained from 1 and 6 , respectively, with 3,6-diphenyl-1,2,4,5-tetrazine. Compounds 1 and 6 are less reactive dienophiles than other strained cyclic olefins as shown by kinetic measurements.     

Zur frage transanularer II-II-wechselwirkungen im [2.2]metacyclophan, [2.2]Paracyclophan und 2,2′-spirobiindan

Concerning the question of transanular II-II-interactions in [2.2]metacyclophane, [2.2]paracyclophane and 2,2′-spirobiindane.From the quotient of the two dissociation constants (K₁/K₂) of [2.2]metacyclophane-bis-chromtricarbonyl (9·0 ± 1·9) it was concluded that there are no transanular II-II-interactions between the two benzene rings. The corresponding values for the bis-chromtricarbonyl-complexes of 2,2′-spirobiindane and [2.2]paracyclophane are 8·0 ± 1·5 and 10⁴, resp. These results are supported by IR-spectroscopical data of the CO-frequencies of the Cr(CO)₃-complexes of [2.2]metacyclophane and some derivatives, of 2,2′-spirobiindane and [2.2]paracyclophane.Moreover, UV-spectroscopic studies of tetracyanoethylene complexes of arenes are shown to be insignificant with regard to transanular II-II-interactions.     

Vapor deposition polymerization of heteroatom-bridged [2.2]paracyclophanes: 1,9-dithia[2.2]paracyclophane and 1,9-dithia[2.2]paracyclophane-1,1,9,9-tetroxide

1,9-Dithia[2.2]paracyclophane-1,1,9,9-tetroxide ( 3 ) was synthesized as white needles in a high yield from 1,9-dithia[2.2]paracyclophane ( 2 ) by oxidation with m-chloroperbenzoic acid, and its molecular structure was determined with single-crystal X-ray diffraction analysis. Vapor deposition polymerizations of 2 and 3 gave amorphous and brittle polymer films along with considerable amounts of nonpolymeric byproducts. A polymer film from 2 was a copolymer of p-(phenylene-methylenesulfide) with p-(phenylene-methylene) units, and a polymer film from 3 was a homopolymer of p-(phenylene-methylene) units with head-to-tail, head-to-head, and tail-to-tail placements. The elimination of sulfur atoms in 2 and sulfone units in 3 took place during their pyrolysis reactions. Plausible mechanisms for vapor deposition polymerizations of both cyclophanes are proposed. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1892–1900, 2001     

Versuche zur Synthese von [2.2]- und [2.3]Cyclopentadienophanen

Synthetic Attempts towards [2.2]- and [2.3]Cyclopentadienophanes . The first [2.2]Cyclopentadienophane (=2,2,3,3,8,8,9,9-octamethyltricyclo[8.2.1.1^4,7]tetradecatetraene; 1b ) has been synthesized (Scheme 5) by reductive coupling of 6,6-dimethylfulvene 3 → 5 (50%) followed by base-induced twofold condensation of 1,2-di(cyclopentadienyl)-1,2-dimethylbutane 5 with acetone to give difulvene 15 (95%). Reductive coupling of 15 gives a complex mixture of tautomers of 16 , 17 , and 1b , which contains ca. 50% of the target molecule 1b . Other synthetic attempts towards [2.2]cyclopentadienophanes 1a and 1b and [2.3]cyclopentadienophane 18 are discussed.     

BIRCH-Reduktion von [2.2] Metacyclophan

Metal-ammonia-reduction of [2.2] metacyclophan led to 5, 8, 13, 16-tetrahydro-[2.2] metacyclophan (II). The structure of this new ring system was confirmed by UV.-, NMR.-and mass spectra analyses. The NMR.-spectrum of II in solution shows an AA′ BB′-system for the -CH₂CH₂-groups. This part of the spectrum is temperature dependant. It collapses and coalesces to a broad singlet at approximately 145°C. A chair-like conformation and conformational changes of II are discussed.     

Heats of formation of [2.2]paracyclophane-1-ene and [2.2]paracyclophane-1,9-diene - an experimental study

The enthalpies of formation [Delta(g)] of tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) = 34.7 kcal mol(-)(1), SE(3) = 42.0 kcal mol(-)(1)] have been derived from the gas-phase heats of formation and are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1 kcal mol(-)(1) for the parent tricyclo[8.2.2.2(4,7)]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol(-)(1)) are in accord with the well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and 3 at one of two bridging corners.     

Synthesis and ring-opening metathesis of tetraalkoxy-substituted [2.2]paracyclophane-1,9-dienes

Tetraalkoxy-substituted [2.2]paracyclophane-1,9-dienes can be prepared in three steps from dithia[3.3]paracyclophanes. A mixture of pseudo-geminal and pseudo-ortho diastereomers is produced and the pure compounds can be separated by fractional crystallization. The solid state structures of these diastereomers reveal strongly distorted aromatic rings consistent with high levels of ring strain. Reaction of these diastereomers with the second generation Grubbs catalyst shows that only the pseudo-geminal isomer can be ring opened to give cis,trans-distrylbenzenes. The origin of this selectivity is discussed and the photoisomerization of the as-formed cis,trans-product to the all trans isomer is demonstrated.     

Zur elektronischen struktur von 6,6′-dimethylfulven und spiro[2.4]Hepta-4,6-dien

The electronic structure of cations 1 and 2 is compared with those of the neutral compounds 3–5. Distinction about the magnitude of aromatic character in the five-membered ring of 3 and 4 vs 5 is made using ¹³C-nuclear magnetic resonance. The results of the experimental investigations are compared with those derived from optimized semi-empirical MINDO/2 calculations using Ruedenberg's energy partitioning technique.     

基于对环芳烷骨架的邻碘苯磺酸类催化剂的合成及其催化氧化性能

以对环芳烷为基本骨架结构,经磺化、上保护和脱氢上碘反应合成了新的邻碘苯磺酸类催化剂4-磺酸基-5-碘-[2.2]对环芳烃,其结构经¹H NMR, ¹³C NMR, IR, MS和元素分析表征。并以2,5-二甲基苯酚为底物,测试其催化效率。结果表明最佳反应条件为：催化剂用量为5 mmol%,在过硫酸氢钾复合盐（1 eq.）和10 mmol%四丁基硫酸氢铵存在下,在干燥碳酸二甲酯中于室温反应24 h,产物环化二聚体收率85%。