Valence tautomers of dimethyl cycloocta-2,5,7-triene-1,4-dicarboxylate and an iron tricarbonyl complex therefrom

Carboxylation of cyclooctatrienyldilithium, Li₂C₈H₈, gives predominantly tricyclo[5.1.0.0^2,4]oct-5-ene-3,8-dicarboxylic acid and trans,cis,cis,trans-deca-2,4,6,8,-tetraene-1,10-dioic acid; in addition, a small quantity of cycloocta-2,5,7-triene-trans-1,4-dicarboxylic acid has been identified as its dimethyl ester. The tricyclooctene diester is in equilibrium with a small amount of the isomeric cis-disubstituted cycloocta-2,5,7-triene in solution, and heating such a solution results in formation of a dimer. Reaction of the tricyclooctene diester with iron pentacarbonl produces exo(2–5)η-(3,8×-dicarbomethoxybicyclo[4.2.0]octa-2,4-diene]tricarbonyliron.     

Electrocyclic reactions of tetraenes: Influence of terminal substituents

Conjugated tetraenes with both central double bonds of cis configuration undergo a series of thermal reactions, the observable products being markedly dependent on the nature of the terminal substituents. Dimethyl 2E,4Z,6Z,8E-decatetraene-1,10-dioate (16) was prepared and found to cyclize readily at 50° to trans dimethyl 2,4-bicyclo[4.2.0)octadiene-6,7-dicarboxylate (18). This reaction proceeds to equilibrium, and the rates and equilibrium constants at the indicated temperatures are: 3.0 × 10^-5 sec^-1 ?40°; 8.2 × 10^-5 sec^-1, 16.0,50°; ?10.0,75°; ?7.47,100° with the equilibrium favoring (18). A sample of 1,8-diphenyl-1E,3Z,5Z;7E-octatetraene (1) showed no reaction below 120°, and at 175° all trans 1,8-diphenyl-octatetraene, cis and trans stilbenes, trans-5-phenyl-6(cis-styryl)-1,3-cyclohexadiene cis-5-phenyl-6-(trans-styryl)-1,3-cyclohexadiene, and cis and trans 6,8-diphenyl-tricyclo[3.2.1.0^2.7]oct-3-enes were formed. At 100° in the presence of excess dimethyl acetylenedicarboxylate 1 gave dimethyl trans-3,4-diphenyltricyclo[4.2.2.0^2.5]deca-6,9-dien-6,7-dicarboxylate. Finally 1,4-di(1-cyclohexen-1-yl)-1,3-batadiyne, hydrogenated over a Lindlar catalyst, gave only tricyclo[10.4.0.0^6,11]hexadeca-1,3,5-triene.     

Reaction of benzyne with cycloheptatriene preparation and thermolysis of some benzo(C9H10) hydrocarbons

The title reaction gave a 2+2 cycloadduct, 8,9-benzo-cis-bicyclo[5.2.0]nona-2,4,8-triene 7, together with ene product, 7-phenylcycloheptatriene. The structure of 7 was confirmed by catalytic reduction to give 8,9-benzo-cis-bicyclo[5.2.0]non-8-ene, which was also obtained in the reaction of benzyne with cycloheptene, and by reduction of the known 8,9-benzobicyclo[5.2.0]nona-1,8-diene. Other benzo(C₉H₁₀) hydrocarbons which have been synthesised are 7,8-benzobicyclo[4.2.1]nona-2,4,7-triene 5, 2,3-benzobicyclo[6.1.0]nona-2,4,6-triene 28 and 4,5-benzobicyclo[6.1.0]nona-2,4,6-triene 29. The thermolysis of 7, 28, 29 and of 3,4-benzo-exo-endo-tetracyclo[4.3.1.0^3,4.0^7,9]dec-3-en-10-one, 25, is described.     

Crystal Structure Analysis of a trans,trans-Cyclodeca-1, 6-diene Derivative

An X-ray crystal structure analysis of the higher melting diastereoisomer of 2,7-dibromo-3,8-dimethoxy-trans,trans-cyclodeca-1,6-diene (Monoclinic; a = 5.76, b = 10.43, c = 11.32 Å, β = 94.04°; space group P2₁/n; Z = 2) has confirmed the NMR. assignment of the molecular conformation and the trans configuration of the methoxy groups. The trans,trans-cyclodeca-1,6-diene ring adopts a centrosymmetric crown conformation with a C? C?C? C torsion angle of 162°.     

Phenylene vinylene oligomers studied by theoretical methods: Joint analysis of computational and x-ray results of the configurational isomers of 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene

The configurational isomers of 1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene have been investigated by ab initio and MOPAC-AM1 semiempirical methods. The calculations were guided by and compared with single crystal X-ray results of the trans, trans-isomer (taken from the literature) and of the cis,cis-isomer (reported here). Using 4-21G-based ab initio calculations, free state geometries, deviations from coplanarity, and barriers to rotation of the central and peripheral rings were evaluated. Such barriers were also enumerated for the solid state of the cis,cis- and trans,trans-isomers. A single-molecule cluster surrounded by point charges sufficed to rationalize observed solid state properties in the trans,trans-isomer, including the quasi-free rotation of the central ring. A multimolecule cluster, however, was required to rationalize the restricted rotation of the rings in the cis,cis-isomer. MOPAC-AM1 methods were used to calculate geometries and energies of rotameric forms on the singlet photoisomerization path cis,cis → cis,trans → trans,trans. Finally, UV absorption wavelengths and oscillator strengths were calculated and the electronic structure of the states discussed. © 1996 by John Wiley & Sons, Inc.     

Thermisches Verhalten von o-Dipropenylbenzol,Beispiel einer aromatischen [1,7]-sigmatropischen H-Verschiebung. Vorläufige Mitteilung

cis, cis-, cis, trans- and trans, trans-o-Dipropenylbenzene (cis, cis-, cis, trans- and trans, trans- 1 ) were prepared. At 225° cis, cis- 1 isomerises to give cis, trans- 1 and vice versa. The isomerisation follows 1. order kinetics. At equilibrium 89% cis, trans- and 11% cis, cis- 1 are present. It is shown by deuterium labelling that the isomerisation is due to aromatic [1, 7 a] sigmatropic H-shifts. trans, trans- 1 rearranges at 225° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 3 ). This can be visualized by disrotatory ring closure of trans, trans- 1 followed by an aromatic [1, 5 s] H-shift. When cis, cis- or cis, trans- 1 are heated for 153 hrs at 225° a small amount (3%) of 1-ethyl-1,2-dihydronaphthalene ( 5 ) is formed.     

The synthesis and structure of 10,11-bistrifluoromethyl-i,o-bicyclo[7.2.2]trideca-10,12-diene. A highly strained inside-outside bicycloalkane derivative.

10,11-Bistrifluoromethyl-i,o-bicyclo[7.2.2]trideca-10,12-diene has been prepared by the Diels-Alder addition of hexafluoro-2-butyne to cis, trans-cycloundeca-1,3-diene. Purification was accomplished via formation of an iron tricarbonyl complex whose structure was established via X-ray crystallography.     

Konfigurationen und Konformationen von zwei 2,4,6,8-Tetrabrom-cyclooctan-1, 5-dionen

The two isomeric tetrabromides, α-isomer mp. 198° and β-isomer mp. 226° described in [1], are identified as cis, cis, trans-2, 4, 6, 8-tetrabromo-cyclooctane-1, 5-dione ( 2 ) and cis, trans, cis-2, 4, 6, 8-tetrabromo-cyclooctane-1, 5-dione ( 3 ) by an analysis of their NMR.-spectra which also allows a derivation of their preferred conformations. Both exist in solution as boat-chair conformers, the geometries of which correlate well with the IR.- and UV.-spectra.     

The molecular structure of trans- and cis-bicyclo-[4.3.0]nonane in the gas phase,studied by electron diffraction and molecular mechanics

The structure and conformations of trans- and of cis-bicyclo[4.3.0]nonane have been studied in the gas phase. Molecular mechanics calculations applying the force field of Ermer and Lifson were used to obtain geometrical constraints, vibrational amplitudes and perpendicular vibrational corrections. The vibrational parameters were corrected for the large amplitude motion of the five-membered ring. The refinement for the trans-isomer confirms completely the predictions of the force field calculations. Although a stable solution could not be obtained for the cis-compound there is no contradiction between experiment and model calculations. The cyclohexane ring in both isomers is found to have a distorted chair conformation. In the cis-isomer it is flattened along the junction and more twisted in the other part. For the trans-compound the reverse is true.The following structural parameters r_g, r_α-structure) are put forward, (a) trans-compound: C₂-symmetry, _r(C-C)_av = 1.536 Å. Average bond angle and average torsion angle in the cyclohexane ring are 110.2° and 58.1°, respectively. The connection angle, defined as the angle between the planes bisecting C6-C1-C5-C9 and C2-C1-C5-C4, is 180°. (b) cis-compound: no symmetry, r(C-C)_av = 1.536 Å. Average bond and torsion angles in the cyclohexane ring are 112.2° and 52.3°, respectively. The connection angle is 124.8°.A comparison is made with structures of related compounds.     

Synthesis and pharmacological activity of silyl isoxazolines 2

Silyl isoxazolines have been synthesized by [2+3] cycloaddition reaction of nitrile oxides to vinyl- and allylsilanes. The addition of 3-pyridylnitrile oxide to 1,3-divinyl-1,1,3,3-tetraphenyldisiloxane affords 1,3-bis{5-[3-(3-pyridyl)isoxazolin-2-yl]}-1,1,3,3-tetraphenyldisiloxane; the latter exists as a mixture of trans- and cis-isomers.The bond angle of the Si–O–Si fragment in thetrans-isomer equals 180(3)° and in the cis-isomer it is 162(3)°.The pharmacological properties of 4-[3-(5-trimethylsilylisoxazolin-2-yl)]pyridinium-chloride have been studied.     

Die thermische Umlagerung von 2-(Buta-1′,3′-dienyl)-phenolen in 2-Alkyl-2H-chromene; Beispiele für aromatische [1,7a]- und [1,5s]sigmatropische Wasserstoffverschiebungen

2-(1′-cis,3′-cis-)- and 2-(1′-cis,3′-trans-Penta-1′,3′-dienyl)-phenol (cis, cis- 4 and cis, trans- 4 , cf. scheme 1) rearrange thermally at 85–110° via [1,7 a] hydrogen shifts to yield the o-quinomethide 2 (R ? CH₃) which rapidly cyclises to give 2-ethyl-2H-chromene ( 7 ). The trans formation of cis, cis- and cis, trans- 4 into 7 is accompanied by a thermal cis, trans isomerisation of the 3′ double bond in 4. The isomerisation indicates that [1,7 a] hydrogen shifts in 2 compete with the electrocyclic ring closure of 2 . The isomeric phenols, trans, trans- and trans, cis- 4 , are stable at 85–110° but at 190° rearrange also to form 7 . This rearrangement is induced by a thermal cis, trans isomerisation of the 1′ double bond which occurs via [1, 5s] hydrogen shifts. Deuterium labelling experiments show that the chromene 7 is in equilibrium with the o-quinomethide 2 (R ? CH₃), at 210°. Thus, when 2-benzyl-2H-chromene ( 9 ) or 2-(1′-trans,3′-trans,-4′-phenyl-buta1′,3′-dienyl)-phenol (trans, trans- 6 ) is heated in diglyme solution at >200°, an equilibrium mixture of both compounds (～ 55% 9 and 45% 6 ) is obtained.     

Synthese und pericyclische Reaktionen von 4, 4a-Dehydro-α-bicyclofarnesensäureester

The title compound 3 was isolated after pyrolysis of cis/trans- 1 at 240°, respectively of cis/trans- 8 at 156°. Thermolysis of cis/trans- 8 at 111° resulted in the deconjugated product 9 , which subsequently could be rearranged via a [1,7] H-shift preferentially into the trans-isomer of 8 . Upon heating at 250°, 3 underwent a series of pericyclic reactions to furnish 11 , whereas epi- 3 did not react under these conditions.     

On the mechanism of the reductive cleavage of anti-9-phenyl-cis-bicyclo[6.1.0]nona-2,4,6-triene

Treatment of the title compound (1a) with potassium in liquid ammonia at ca ?33° immediately afforded the benzylcyclooctatetraene dianion (4a) which, upon quenching with iodine-pentane, gave benzylcyclooctatetraene (5) as the only isolable product. In contrast, treatment of1a with potassium amide in liquid ammonia at ?69° initially afforded the 9-phenylmethylenecyclooctatrienyl anion (6a) as a short-lived intermediate which was then converted to the α-aminobenzylcyclooctatetraene dianion (7a). These results, coupled with the observation that cis-bicyclo[6.1.0]nona-2,4-diene (12) in potassium amide-liquid ammonia affords the cis-bicyclo[6.1.0]nonadienyl anion (8b) which then slowly opens to the methylcyclooctatetraene dianion (4b) at ?12°, lead to the conclusion that4a is produced by a reductive cleavage of1avia a radical anion or dianion.     

Delocalization resonance energy of the allylic radical from the geometrical isomerization of hexa-1,3,5-trienes

Thermal cis, trans geometrical isomerization theoretically involves a 90° twisted, singlet diradical-like transition state which may serve as a base for the examination of structural perturbations. Although thermal rearrangement of hexa-1, trans-3,5-triene (and all-trans octa-2,4,6-triene) to the cis isomer cannot be followed directly owing to subsequent cyclization and 1,5 hydrogen shifts, activation parameters for disappearance have been determined. Experimental complications and mechanistic uncertainties which make interpretation difficult are removed in the bicyclic hexatriene, cyclopentenylidenecyclopentene. These geometrical isomers undergo uncomplicated thermal cis, trans isomerization in vessels of lead-potash glass: log k₁ = 12·03±0·32?41·7±0·8/(0·004575T_abs). Extraction of a value for allylic delocalization energy from the behavior of hexa-1, trans-3,5-triene [log k₁ = 12·91 ± 0·47?44·3±1·2/(0·004575 T_abs)] requires corrections of the Dewar-Schmeising type for changes in hybridization of the σ bonds. Depending on whether ethylene or trans-butene is taken as standard, values of 12·2 and 13·1 kcal/mol are obtained (estimated uncertainty ± 2 kcal/mol).     

Hexafluorothioacetone based synthesis of fluorinated heterocycles

Cycloadducts of hexafluorothioacetone (HFTA) were prepared in high yield by a CsF catalyzed reaction between readily available 2,2,4,4-tetrakis-(trifluoromethyl)-1,3-dithietane (as a source of HFTA) with conjugated electron-rich hydrocarbon dienes, such as cyclopentadiene, 2,3-dimethylbuta-1,3-diene, cyclohexa-1,3-diene or (1Z,3Z)-cyclohepta-1,3-diene. Cyclohexa-1,4- and (1Z,5Z)-cycloocta-1,5-dienes, also undergo the reaction with in situ generated HFTA, but form the products of insertion of HFTA into the C-H bond of the diene as a result of ene-reaction. The highly selective reaction of HFTA with (1Z,3Z,5Z)-cyclohepta-1,3,5-triene and (1Z,3Z,5Z,7Z)-cycloocta-1,3,5,7-tetraene leads to the formation of cycloadducts derived from exclusive addition of thioacetone to the corresponding bicyclic isomers—bicyclo[4.1.0]hepta-2,4-diene or bicyclo[4.2.0]octa-2,4,7-triene, respectively. The corresponding cycloadducts of HFTA with 2,3-dimethylbutadiene-1,3-cyclohexa-1,3-cyclohexa-1,4-dienes and (1Z,3Z,5Z)-cyclohepta-1,3,5-triene were also prepared by direct reaction of sulfur/hexafluoropropene/KF and the corresponding hydrocarbon substrate at 35-45 °C in DMF.     

Synthese und Chiralität der stereoisomeren Achillene,Achillenole und Hymentherene

(+)-cis-Achillene ( 10 ) and (?)-trans-achillenol (7), two monoterpenes recently isolated [1] from the essential oil of Achilleafilipendulina, were synthesized, together with their stereoisomers (?)-(9) and (+)-(8), starting from (S)-(+)-2,6-trans-dimethylocta-1,3, 7-triene ( 1 ). The isomeric ß-hymen thereties ((?)- 3 and (+)-4), often quoted [2] [3] [4] but never isolated, were obtained as intermediates. The mode of synthesis chosen establishesis (R)-chirality for naturally occurring (?)-trans-achillenol (7) and (+)-cis-achillene ( 10 ) as well as for the purely synthetic 4, 7-diene derivatives described in this paper.     

Metals in organic syntheses: XIV. NMR,IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes

Among the several hydrides formed when trans-[PtHClL₂] (L = PPh₃) reacts with Sncl₂, only trans-[PtH(SnCl₃)L₂] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl₃)L₂]. At −10°C, cis-[PtEt(SnCl₃)L₂] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable.At −50°C, a mixture of trans-[PtHClL₂] and trans[PtH(SnCl₃)L₂] reacts with ethylene to give cis-[PtEtClL₂] and cis-[PtEt(SnCl3)L₂] and this has been attributed to the catalytic activity of SnCl₂ which dissociates from cis-[PtEt(SnCl₃)L₂] at this temperature.Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl₃)L₂], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L₂]⁺ SnCl₃⁻. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L₂], trans-[Pt(SnCl₃)(COEt)L₂], trans-[PtCl(COEt)l₂ · SnCl₂], and trans-[Pt(COEt)(CO)L₂]⁺ SnCl₃⁻. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL₂] with SnCl₂.Trans-[PtH(SnCl₃)L₂] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl₃)(CO)₂L₂], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl₃)L₂] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl₃)L₂] is allowed to react with CO.The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.     

Planoid distortions in bridged spirocompounds : Formation of (all-cis)-[5.5.5.5]fenestrane in the attempted synthesis of the (cis,cis,cis,trans)-isomer

Molecular distortions in bridged [4.4]spirononanes and fenestranes are discussed in terms of symmetry deformation coordinates. This analysis reveals that the central, quaternary carbon atom in most of these compounds shows mainly a decrease of the two opposite ring bond angles, whereas the distortions in fenestranes are dominated by an increase of the two opposite bond angles. Dicyclopentadienone 8 serves as the starting material for the preparation of [5.5.5.5]fenestranes. In the key step of the synthesis, the Pd-catalyzed reductive transannular reaction of the enaminonitrile 13 and the ketolactone 17, (all-cis)[5.5.5.5]fenestrane 6 is formed instead of the (cis,cis,cis,trans)-isomer 7.     

Applications of molecular mechanics calculations in carbohydrate chemistry. I. Conformational and constitutional equilibria of tetraoxabicyclo[4.4.0]- and -[5.3.0] decanes,bicyclic diacetals of alditols

The energies of various conformations have been calculated by molecular mechanics for cis and trans isomers of 2,4,7,9-tetraoxabicyclo[4.4.0] decane and 3,5,8,10-tetraoxabicyclo[5.3.0]decane and their methyl derivatives. These molecules are models for reaction products from formaldehyde and the tetrols, pentitols, and hexitols. The conformational equilibria were analyzed for the cis-bicyclo [4.4.0] and cis-bicyclo[5.3.0] systems and compared with available experimental data. The thermodynamic stability of bicyclo[4.4.0] products was found to be higher than that of bicyclo[5.3.0] derivatives in the gas phase in every case studied. Discrepancies with experimental data that exist in a few cases can be ascribed to solvent effects.     

Zur reaktivität komplexgebundener carbocyclen : V. Synthese un thermisches verhalten neuartiger cyclooctatrien- und cyclononatrien-eisencarbonylkomplexe

The reaction of cycloocta-1,3,5-triene and cycloocta-1,3,6-triene with Fe₂(CO)₉ has been reinvestigated under mild conditions. Two stable complexes of cycloocta-1,3,6-triene have been obtained as well as the previously unknown 1,3,5-C₈H₁₀Fe₂(CO)₇. All three complexes rearrange at 65°C to the known 1,3,5-C₈H₁₀Fe₂(CO)₆. Cyclonona-1,3,6-triene reacts at room temperature with Fe₂(CO)₉ to form an unstable tetracarbonyl complex, whereas reaction at 70°C leads to the formation of 1,3,5-C₉H₁₂Fe(CO)₃, which itself can be converted at 100°C to (bicyclo[4.3.0]nona-2,4-diene)Fe(CO)₃. Treatment of bicyclo[6.1.0]nona-2,4,6-triene with Fe₂(CO)₉ in CH₃OH gives (bicyclononatriene)Fe₂(CO)₆, (bicyclononatriene)Fe(CO)₃ and the symmetrical (cyclononatetraene)Fe(CO)₃ exclusively. All compounds were characterised by ¹³C-NMR.