Synthesis of (2Z,6Z,10Z,14E,18E)-farnesylfarnesol,

Nine-step synthesis of the title triterpenol from (E,E)-farnesol using a two-stage cis-C₅-homologation procedure is descrilaed.     

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     

Reactivities of Carbocations and Carbanions

Initiation and propagation rate constants of carbocationic and carbanionic polymerizations can be predicted by the correlation equation log k_{20 °C} = s(N + E), where E characterizes the electrophilicity of carbocations and electron-deficient alkenes, and N characterizes the nucleophilicity of carbanions and electron-rich alkenes. Since the nucleophile-specific slope parameter s is generally close to 1, it can be neglected in a first approximation, and the two-dimensional representation in Figure 3 illustrates the gradual change from carbanionic to carbocationic polymerizations with Hall's “initiation by bond-formation” as the link connecting the two ranges. The value of model studies for understanding ionic polymerizations is illustrated.     

An ab Initio study of conformational properties of (Z,Z)-, (E,Z)- and (E,E)-cycloocta-1,5-diene

Ab initio calculations at HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the three geometrical isomers of cycloocta-l,5-diene 1–3.     

The Reactivity of Potassium Carbanions with Epoxides

Cyclohexene oxide reacted with n-butylpotassium unexpectedly to produce 2-butylcyclohexanone in a 10% isolated yield of its semicarbazone derivative. Based on previous literature, a three-part mechanism is proposed that implies that a yield greater than 33% is not possible.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Stereoselective syntheses of substituted methyl (Z,E,E)-deca-2,7.9-trienoates and substituted methyl (Z,E,E)-undeca-2,8,10-trienoates

Lindlar hydrogenation of substituted methyl ($\text{E}$,$\text{E}$)-deca-7,9-dien-2-ynoates and substituted methyl ($\text{E}$,$\text{E}$)-undeca-8,10-dien-2-ynoates affords selectively the corresponding ($\text{Z}$,$\text{E}$,$\text{E}$)-trienes.     

Z/E PHOTOISOMERIZATION OF UROCANIC ACID*

The E ? Z photoisomerization of the title compound (UA) (a naturally occurring sunscreen) has been studied in aqueous solution. At a UA concentration of 6mM and using 313nm excitation, φ_E→z= 0.52, φ_Z→E= 0.47 and the photostationary state is 34% E. Under these conditions, loss of UA is minimal. Low energy triplet quenchers fail to impede the isomerization, but the reaction can be induced by several triplet sensitizers. The E_T for UA is estimated to be approximately 55 kcal/mol.     

Candidate Trail Attractants of Reticultermes lucifugus: Stereoselective Syntheses of (3Z, 6E,BE)-(3Z, 6E, 8Z)-and (3Z, 6Z, 8Z)-3,6,8 -Dodecatrien-1-OL1

Stereoselective syntheses on a gram scale of (3Z,6E,8E)-, (3Z,6E,8Z)-and (3Z,6Z,8Z)-3,6,8-dodecatrien-1-ol, 8, 9 and 10, respectively, are described. A key step of the synthesis of 8 consisted of a copper-mediated coupling reaction between 4-(2-tetrahydropyranyloxy)-1-butynylmagnesium bromide (15) and the mesyl ester of (2E,4E)-2,4-octadien-1-ol (14). A similar copper-mediated reaction between 15 and the mesyl ester of (E)-2-octen-4-yn-1-ol (19) was used to construct the C-12 carbon skeleton of 9. On the other hand, the synthesis of 10 was based on a palladium-promoted reaction between (Z)-1-bromo-1-pentene (23) and the organozinc bromide derived from 3,6-heptadiyn-1-yl acetate (27).     

Synthese der (1Z,3E) und (1Z,3Z)-isomeren des wisanins

The (1Z,3E)- and (1Z,3Z)-isomers of wisanine were synthesized and characterized by their spectroscopic data.     

Characterization of posticlure and the structure-related sex pheromone candidates prepared by epoxidation of (6Z,9Z,11E)-6,9,11-trienes and (3Z,6Z,9Z,11E)-3,6,9,11-tetraenes

trans-11,12-Epoxy-(6Z,9Z)-6,9-henicosadiene (posticlure) has been identified from a pheromone gland of the lymantriid species, Orgyia postica. Since the diversity of Lepidoptera suggests that some species utilize the structure-related epoxy compound as a sex pheromone component, epoxydienes and epoxytrienes derived from (6Z,9Z,11E)-6,9,11-trienes and (3Z,6Z,9Z,11E)-3,6,9,11-tetraenes with a C₁₉–C₂₁ chain were systematically synthesized and the chemical data were accumulated in order to contribute to a new pheromone research. Peracid oxidation of each triene and each tetraene produced, respectively, a mixture of three epoxydienes (cis-6,7-epoxy-9,11-diene; cis-9,10-epoxy-6,11-diene; and trans-11,12-epoxy-6,9-diene) and four epoxytrienes (cis-3,4-epoxy-6,9,11-triene; cis-6,7-epoxy-3,9,11-triene; cis-9,10-epoxy-3,6,11-triene; and trans-11,12-epoxy-3,6,9-triene). While the 9,10-epoxy compounds were unstable and, interestingly, converted into 9-ketone derivatives after chromatography over SiO₂, each positional isomer was isolated by HPLC equipped with an ODS column, and the chemical structure was determined by NMR analysis. On the GC-MS analysis with a DB-23 column, the positional isomers were also eluted separately and characteristic mass spectra were proposed. By comparing the spectral data of the epoxy compounds with a different carbon chain, diagnostic fragment ions reflecting the chemical structure were determined as follows: m/z 79, 109, 113, and M-114 for the 6,7-epoxydienes; m/z 69, 97, 111, 139, and M-111 for the 9,10-epoxydienes; m/z 57, 79, 109, 136, M-151, and M-111 for the 11,12-epoxydienes; m/z 79, 91, 105, and 119 for the 3,4-epoxytrienes; m/z 79, 124, M-124, M-96, and M-69 for the 6,7-epoxytrienes; m/z 79, 95, 109, 137, and M-108 for the 9,10-epoxytrienes; and m/z 79, 134, M-149, M-109, and M-95 for the 11,12-epoxytrienes.     

E and Z stereoisomers of compounds of the phthalide series

The stereospecific position of the H⁴ proton in the PMR spectra of 3-benzyl-idenephthalides identifies unambiguously the E and Z isomers in a mixture. The IR spectra of off-planar deformation vibrations of the C=C bond in the 990–970 cm^–1 region have strong absorption bands, assigned to the E and Z isomers. The strong short-wave band (260 nm) for 3-benzylidenephthalides, having only one benzene ring in the indan moiety, suggests the presence of the E form (=28,000). The long-wave absorption band at 390–430 nm belongs to the Z isomers (=21,000–31,000). 3-Benzylidenephthalides which have no carbonyl groups in their molecules, show fluorescence (_f1=540–560 nm in EtOH).N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 309–314, February, 1992.