Conformational Properties of (Z,Z)-, (E,Z)-, and (E,E)-Cycloocta-1,4-dienes

Summary.  Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and the MP2/6-31G^*//HF/6-31G^* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C ₂-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C _S-symmetric boat-boat geometry is 19.1 kJ·mol⁻¹. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C ₁) transition state which is 43.5 kJ·mol⁻¹ above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol⁻¹ more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol⁻¹, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol⁻¹. The C _S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C _S) transition state which is 37.2 kJ·mol⁻¹ above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol⁻¹ less stable than the crown conformation. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 3, 2002     

(Z)-1-苯基-1-对氟苯基-2-对甲苯磺酰基-1,4-戊二烯的合成及其晶体结构

通过1-苯基-2-对甲苯磺酰基乙炔、对氟苯基氯化锌及烯丙基溴的三组分串联反应,合成了(Z)-1-苯基-1-对氟苯基-2-对甲苯磺酰基-1,4-戊二烯(1),其结构经1H NMR, 13C NMR, IR, HR-MS和XRD表征.1为Z-构型,属单斜晶系,空间群P21/c, a=9.899 1(20)(A), b=9.621 9(20)(A), c=21.812 9(15)(A), β=95.575(10)°, V=2067.8(6)(A)3, Z=4, Dc=1.254 g·cm3, μ=0.181 mm-1, λ=0.710 73(A), F(000)=816, R=0.046 3, wR=0.134 1.共收集到3 684个独立衍射点,其中I>2σ(I)的可观察点为2 989.     

(Z)-1,4-Diphenyl-2-phenylamino-2-butene-1,4-dione: Synthesis and Mechanizm of Formation

Heating of 1-phenyl-2-(phenylamino)ethanone in a water-ethanol solution of potassium carbonate gave rise to (Z)-1,4-diphenyl-2-phenylamino-2-butene-1,4-dione; it formed most probably by reaction of the initial aminoketone with its oxidation product, 1-phenyl-2-(phenylimino)ethanone.     

Stereocontrolled Preparation of (Z)-1,4-But-2-endiol Estersin Phase-Transfer Conditions

Isomerically pure esters of (Z)-1,4-but-2-endiol are prepared, in satisfactory yields, under phase-transfer conditions.     

Carboalumination-Epoxide Ring Opening for the Formation of 1,4-Disubstituted (Z)-3,6-Alkadienols

Allylalumination of alkynes (i.e. forming Negishi's (Z)‐alkenyl dialkylalane) followed by alkenylation of epoxides provides 1,4‐disubstituted (Z)‐3,6‐alkadienols. The alkenylation can be facilitated by the presence of a neighbouring coordinating group in the epoxides. This "one‐pot" approach has been successfully applied in the large‐scale production of C10–C15 fragment of 9,10‐didehydroepothilone D (a synthetic epothilone analog as an anti‐cancer agent in phase 2 clinical trials).     

Die röntgenstrukturanalysen von (E)- und (Z)-2-Buten-1,4-diyl-dithiocyanat bei 93 K

The X-Ray Diffraction Analysis of (E)- and (Z)-2-Butene-1,4-diyl Dithiocyanate The crystal structure of the (E)- and (Z)-2-butene-1,4-diyl dithiocyanate ( 1 and 2 , respectively) which have been used as substrates for an E′ reaction, has been determined by X-ray analysis. The SCN groups are for both molecules in an anticlinal conformation relative to the double bond. A remarkable intermoecular contact has been observed between the N-atom of one molecule and the S-atom of its neighbour.     

Mild and selective palladium-catalyzed dimerization of terminal alkynes to form symmetrical (Z,Z)-1,4-dihalo-1,3-dienes

A regioselective and stereoselective palladium-catalyzed dimerization of terminal alkynes method for the synthesis of symmetrical (Z,Z)-1,4-dihalo-1,3-dienes is presented. In the presence of a catalytic amount of PdX(2) and 3 equiv of CuX(2) (X = Cl and Br), terminal alkynes were dimerized to afford (Z,Z)-1,4-dihalo-1,3-dienes in good yields. The results showed that the effect of solvent had a fundamental influence on the chemoselectivity of the dimerization reaction. The mechanism of the palladium-catalyzed dimerization reaction is also discussed.     

Chiral 1,4-bis-diphosphine ligands from optically active (Z)-olefines

The catalytic asymmetric hydrogenation of prochiral ketones was carried out with Ru(II) complexes prepared from new chiral diphosphine ligands, cis-(R,R)-2,5-bis[(diarylphosphino)]-3-hexenes. These new ligands were prepared from enantiomerically pure (R,R) or (S,S)-(Z)-3-hexene-2,5 diol and enantiomeric excesses up to 85% were obtained in the reduction of 2-benzamidomethyl-3-oxobutanoate, starting material for the synthesis of 4-acetoxy-2-azetidinone.     

Hydrazinolytic Recyclization of (Z)-3-Acetyl-2-methyl-2,3-dihydro-1,4-benzodioxin-2-ol

A convenient preparative method has been developed for obtaining previously unknown 4-(o-hydroxyphenoxy)-substituted pyrazoles by the reaction of (Z)-3-acetyl-2-methyl-2,3-dihydro-1,4-benzodioxin-2-ol with hydrazine.     

Sex Pheromone of Chilo Suppressalis: Efficient Syntheses of (Z)-11-Hexadecenal, (Z)-13-Octadecenal And (Z)-9-Hexadecenal

The constituents of the sex attractant pheromone of Chilo suppressalis: (Z)-11-Hexedecenal 1, (Z)-13-octadecenenal 2 and (Z)-9-Hexadecenal 3 have been synthesized as their ethylene acetals 19, 15 and 13, in six steps from easily available compounds. The synthetic methodology can be applied to preparative scale.