Exo Double Bond Research Articles

Comparative behaviour of cyclic versus acyclic olefins in the stereochemistry of the metathesis reaction with group VI metal-based catalysts

Metatheses of cis-2-pentene and norbornene have been carried out with Group VI metal-based catalysts associated with various co-catalysts. With cis-2-pentene the stereoselectivity has been determined by the trans/cis ratios of 2-butenes and 3-hexenes extrapolated to zero percent conversion. With norbornene, the percentage of double bonds in the polymer has been determined by 1H NMR and 13C NMR. The tungsten precursor complexes used were of the type W(CO) 5L, W(CO) 4L 2, W(CO) 3(arene), W(CO) 4X 2, WCl 6, W(OPh) 6, WOCl 4 and Mo(CO) 3(arene), MoCl 5, Mo(NO) 2X 2L 2 and (Mo(NO) 2X 2) n. The chromium precursor complex was Cr(CO) 3(arene). The co-catalysts used were Me 3Al 2Cl 3, EtAlCl 2 (with or without O 2, C 2H 5OH, C 2H 5OCP 2H 5, 2,6-dichlorophenol, 2,6-diisopropylphenol, 1,3-diphenyl-2-propanol), SnMe 4, SnPh 4, CCl 4 + hν, AlX 3. With norbornene, the percentage of cis double bonds was found to be equal to 50 ± 5% corresponding to a random coordination and/or reaction of the exo double bond of the norbornene to the metallacarbene. The value obtained was the same whatever the transition metal, the ligands coordinated to the precursor complex with the co-catalyst. These results contrast sharply with those obtained with acylic olefins using the same or similar catalysts. For example, with cis-2-pentene, there is a strong effect of the transition metal on the resulting stereochemistry. The retention of the configuration of the starting olefin increases in the order W < Mo < Cr. It seems also that there is a slight but meaningful effect of ligand, especially with molybdenum. A general explanation is given on the origin of stereoselectivity in the metathesis of acyclic and cyclic olefins, which is based on the relative stabilities of the coordinated olefin and of the metallacyclobutanes. If the centages of cis and trans protons assuming the same relaxation time for both types of protons. In any case the repetition time was large enough. The results obtained by both methods in the same sample gave us the same percent of cis double bonds.

Reaction of superoxo Co(III) complexes with 2,6-di- [formula omitted]-butyl- [formula omitted]-benzoquinone methides

Superoxo Co(III) complexes derived from Co(Salpr) and [Co(CN) 5] 3− reacted with 2,6-di- t -butyl- p -benzoquinone methides to give 2,6-di- t -butyl- p -benzoquinone and 2,6-di- t -butyl-2,5-cyclohexadienonespirooxiranes as the main products, which are considered to result from nucleophilic attack by the superoxo species on the exo double bond of the quinone methides.

Structure and absolute stereochemistry of the sesquiterpene alcohol (–)-myliol: X-ray analysis of the p-bromobenzoate

The structure and absolute configuration of the novel sesquiterpene alcohol, (–)-myliol (C15H22O) have been determined by X-ray analysis of its p-bromobenzoate (III). Crystals of the p-bromobenzoate (III) are triclinic, space group P1, a= 10.37(1), b= 10.20(1), c= 10.39(1)Å, α= 107.8(1), β= 71.6(1), γ= 110.3(1)°, Z= 2, with two independent molecules in an asymmetric unit. The structure was solved by the heavy-atom method, and refined by block-diagonal least-squares to R 0.085 over the 1 956 independent observed reflections. The absolute configuration was determined by the anomalous dispersion effect. The two molecules in the asymmetric unit have similar geometries, and each contains a novel fused 5,3,6,3-tetracyclic ring system. The two cyclopropane rings in this fused ring are in conjugation and the central cyclopropane ring conjugates further with an exo-double bond. The cyclopentane ring in this skeleton has an envelope conformation and the cyclohexane ring is considerably distorted by the two fused cyclopropane rings.

Epoxide Rearrangement III. Isomerization of 1-Methylcyclohexene Oxide over TiO2–ZrO2, NiSO4 and FeSO4

Abstract The reaction of 1-methylcyclohexene oxide at 108 °C was found to give predominantly 2-methylcyclohexanone (III) over FeSO4, but predominantly allyl alcohols (VI) over TiO2–ZrO2 of various compositions. NiSO4 gave the same amount of both products, III and VI. The selectivities over FeSO4 and NiSO4 were not much varied with calcination temperatures from 150 °C to 700 °C, while the catalytic activities were higher with NiSO4 calcined at low temperature and with FeSO4 calcined at high temperature. FeSO4 and NiSO4 gave the preferential formation of an allyl alcohol with exo-double bond, 2-methylene cyclohexanol (VIa), while TiO2–ZrO2 formed predominantly an allyl alcohol with endo-double bond, 2-methyl-2-cyclohexene-1-ol (VIb). Both the acidity and basicity of TiO2–ZrO2 were observed to increase by mixing each oxide and to correlate with the catalytic activity. The allyl alcohol formation was explained by an acid-base bifunctional mechanism.

Studies on Fungicides. XXII. Reaction of Dimethyl Acetylenedicarboxylate with Dithiocarbamates, Thiolcarbamates, Thiosemicarbazides and Thiosemicarbazones

Dimethyl acetylenedicarboxylate was found to react readily with dithiocarbamates, thiolcarbamates, thiosemicarbazides and thiosemicarbazones to give 4-thiazolidones (I, IV, V, VI and VII). The exodouble bond of 4-thiazolidones (I) was highly reactive to dithiocarbamates to give 2, 2'-dithioxo-5, 5'-bi-4-thiazolidones (II), which were autoxydized to 2, 2'-dithioxo-Δ5, 5'-bi-4-thiazolidones (III) in the presence of catalytic amount of amines.

Polyacetylenes of Solidago virgaurea: Their seasonal variation and NMR long-range spin coupling constants

Great variation in polyacetylene content with season was noted in this plant. The major compounds present are 2,8- cis- cis-matricaria ester (I), two matricaria-γ-lactones (II and III), and one lachnophyllum lactone (IV). Two epoxides and an acetylenic hydrocarbon are present in the roots, whereas no acetylenic compound could be detected in the aerial parts of the plants. The exo double bond cis- trans relationship between II and III was established from NMR long-range couplings in these and other protoanemonin derivatives.

Carbonium Ion Polymerization of Norbornene and Its Derivatives

Abstract Cationic polymerizations of various bicyclo-(2,2,1)-heptane olefinic derivatives were examined, and the structures of the resulting polymers determined. Norbornene readily polymerizes to soluble polymer at-78°C, whereas 2-vinyl-5-norbornene yields predominantly soluble polymer at low temperatures (∼-78°C) and largely cross-linked product at higher temperatures (∼-30°C). The major polymerization mechanisms for norbornene and 2-vinyl-5-norbornene are similar. In each case, the reaction proceeds by opening of the endo double bond, and the repeat units are where R is H or vinyl. The reactivity difference between the endo and exo double bonds in 2-vinyl-5-norbornene is most likely due to the strained endo double bond. When the reactivity of the exo bond is enhanced by the introduction of a methyl group (2-isopropenyl-5-norbornene) both double bonds participate simultaneously in the polymerization, and cross-linked products are obtained.

Copolymerization of isopropenyl and isopropylidene oxazolones with styrene

Abstract2‐Isopropenyl‐4‐isopropyl‐2‐oxazolin‐5‐one (M2), was copolymerized with styrene (M1), and the monomer reactivity ratios were determined to be r1 = 0.31 ± 0.03, r2 = 1.12 ± 0.10. New isomerized oxazolones (M2), 2‐isopropylidene‐4‐methyl‐3‐oxazolin‐5‐one, 2‐isopropylidene‐4‐isopropyl‐3‐oxazolin‐5‐one, and 2‐isopropylidene‐4‐isobutyl‐3‐oxazolin‐5‐one were prepared and copolymerized with styrene. The monomer reactivity ratios were: r1 = 0.36 = 0.07, r2 = 0.0; r1 = 0.39 ± 0.06, r2 = 0.00 ± 0.10; r1 = 0.39 ± 0.10, r2 = 0.0, respectively. The isomerized oxazolones showed no tendency towards homopolymerization by radical initiator. From the results of infrared and NMR spectra and hydrolysis of the copolymer, it was indicated that the isomerized oxazolones participated in copolymerization in the form of 1–4 polymerization of the conjugated dienes (exo double bond at C2 and the CN in the ring). Copolymers reacted with nucleophilic reagents such as amines and alcohols.

Notes - Stability and Ease of Formation of Endo and Exo Double Bonds in 5- and 6- Ring Systems

Notes - Stability and Ease of Formation of Endo and Exo Double Bonds in 5- and 6- Ring Systems