Endocyclic Double Bond Research Articles

Conformational flexibility of 1,3-cyclohexadiene and its aza analogs

The conformational flexibility of 1,3-cyclohexadiene and its analogs — pyridine and pyrimidine derivatives— was studied by HF/6-31G** ab initio quantum chemical calculations. The potential surface calculations and normal vibration shape analysis show that the molecules exhibit two weakly coupled ring deformation modes. One of the modes may be described as rotation around the C(sp3)-C(sp2) bond leading to a transition state of the ring inversion process. The other mode involves flattening of the butadiene fragment and a loss of planarity for endocyclic double bonds without any pronounced changes in the conformation of the saturated part of the molecule. An accurate calculation of the ring inversion barrier demands inclusion of electron correlation effects.

The Crystal Structure of Hop-17(21)-en-3β-yl acetate of Pluchea pteropoda Hemsl. from Vietnam

The title compound isolated from the roots of a Vietnamese plant and being known for its activity against fever was identified by this X-ray analysis to be a pentacyclic triterpene of hopanoide type with a C17=C21 endocyclic double bond in the five membered ring. The presence of several axially substituted methyl groups on both the α and β side causes the so called "mid-molecule strain" having already been reported in the literature for other hopane type ring systems.

Peculiarities of electroreduction of trans-2-allyl-6-methyl(allyl,phenyl)-1,2,3,6-tetrahydropyridines

Electrochemical reduction of trans-2-allyl-6-R-1,2,3,6-tetrahydropyridines (R = Me, All, and Ph) on the mercury cathode in anhydrous DMF (with 0.1 M Bu4NClO4 as the supporting electrolyte) resulted in catalytic hydrogen evolution, while in the case of anhydrous DMF the electrochemical activity of the endocyclic double bond was dictated by the nature of the R substituent at the carbon atom neighboring the double bond. The electrocatalytic hydrogenation of the piperideines under study on the Ni (Nidisp/Ni) cathode in 40% aqueous DMF in the presence of a tenfold excess of AcOH yielded the corresponding trans-2-propyl-6-R1-piperidines (R1 = Me, Pr, and Ph). Using trans-2,6-diallyl-1,2,3,6-tetrahydropyridine as an example, the conditions (with annealed copper as the cathode) for selective hydrogenation of the double bonds in allyl substituents with preservation of the endocyclic double bond were found.

Chalcogenatetrasilacyclopentenes: Five-Membered Rings with Endocyclic Si-Si Double Bonds.

The formal [4+1] cycloaddition of the chalcogens S, Se, and Te to the tetrasilabuta-1,3-diene 1 furnishes the molecules 2-4, the first five-membered rings with endocyclic Si-Si double bonds. The new compounds are thermally stable and chemically inert. However, 4 is light-sensitive and decomposes in daylight with deposition of tellurium. R=2,4,6-iPr3C6H2.

Synthesis and characterization of carbon-13 labelled 2-ethylidene-5-norbornene containing EPDM rubber. Observation of crosslinking and oxidation

[2, 8- 13C 2] ENB was synthesized from labelled acetic acid and terpolymerized in a batch reactor to [2, 8- 13C 2] ENB–EPDM rubber ( M w=4.8×10 5, d=3, ENB content ∼8 wt.%, ethene to propene ratio ∼1.8). Labelled ENB, its precursors and the EPDM were characterized by NMR spectroscopy. ENB is incorporated in the polymer chain through the endo cyclic double bond. Upon high temperature exposure to air of an NMR sample, the number of double bonds decreases due to crosslinking via addition of backbone radicals to double bonds. Some oxidation of double bonds occurs, giving rise to acetyl norbornene units. No significant cleavage of double bonds takes place. The labelling/NMR approach provides an excellent tool for studying (minor) chemical conversions in EPDM rubber.

Enamino Ester Reduction: A Short Enantioselective Route to Pyrrolizidine and Indolizidine Alkaloids. Synthesis of (+)-Laburnine, (+)-Tashiromine, and (-)-Isoretronecanol.

Various chiral pyrrolidine tetrasubstituted beta-enamino esters were reduced catalytically or chemically with good to moderate diastereoselectivity owing to a chiral induction originated from (S)-alpha-methylbenzylamine. With endocyclic double bond compounds, the best result was obtained using PtO(2) as hydrogenation catalyst and led to a major syn addition product (e.d. 90%). In the case of exocyclic double bond compounds, hydrogenation over Pd/C gave rise to the higher diastereoselectivity and mainly afforded the unexpected anti addition product (e.d. 84%). The scope of these reductions has been extended to the synthesis of three pyrrolizidine or indolizidine alkaloids: (+)-tashiromine, (+)-laburnine, and (-)-isoretronecanol. Syntheses of these natural products, starting from chiral beta-enamino diesters, were achieved in a short and convenient manner, leading to enantiopure compounds in good overall yields.

Copolymerization of ethylene with 2,5-norbornadiene using a homogeneous metallocene/MAO catalyst system

Copolymerization of ethylene with a symmetrical diene, namely, 2,5-norbornadiene was studied using a homogeneous metallocene/MAO catalyst system. Copolymerizations were found to occur exclusively through one of the two equally reactive endocyclic double bonds with Cp 2 ZrCl 2 , (buCp) 2 ZrCl 2 and Et(Ind) 2 ZrCl 2 catalysts. Both double bonds are involved in the polymerization when Me 2 SiCp 2 ZrCl 2 is used as the catalyst. In the case of Et(Ind) 2 ZrCl 2 , the incorporation of the diene was found to increase with time. The extent of incorporation of the diene, molecular weight and copolymerization activity were found to depend on the nature of the catalyst.

Diels-Alder reaction of R-(−)-carvone with isoprene

Diels-Alder reactions of R-(−)-carvone with isoprene using different Lewis acids as catalysts have been studied. The best results were obtained with EtAlCl 2 at 25°C for 48 hours. The yields are quantitative and the d.e. is 86.8%. Regioselective dihydroxylation at the endocyclic double bond of the cycloadduct followed by acetonation gave a crystalline acetonide, the structure and stereochemistry of which were confirmed by an X-ray crystallographic analysis. Hence the stereochemical outcome of the Diels-Alder reaction is now established and the reaction occurred preponderantly in an anti orientation with respect to the isopropylene group in R-(−)-carvone.

The thermodynamic stabilities of tricyclic tetraene C12H12 hydrocarbons

The thermodynamic stabilities and heats of formation of tricyclic C12H12 tetraenes 1–6 as well as of a truncated tetrahedron hydrocarbon isomer 7 were computed by various density functional methods in conjunction with a polarized double-ζ basis set. As the DFT stabilities of 1–7 differ significantly from the MM2, MM3, MM4 and AM1 results, we conclude that these empirical and semiempirical methods are inappropriate to study such polycyclic hydrocarbons. Compound 6 with only endocyclic double bonds, a potential synthetic precursor of 7, is found to be less favorable energetically than the other isomers. Although the Csp3–Csp3 single bonds in 1–6 are rather long (1.601 to 1.620 A) due to a combination of ring strain and hyperconjugation, the small nucleus-independent chemical shift (NICS) values of 1 and 6 confirm the expectation that cyclic electron delocalization is lacking. In contrast, NICS is unusually large in the cage center (–14.6) of 7, but this is due to the cumulative diatropic influence of the four cyclopropane rings.

Syntheses in the Isocamphane Series XLII [1]. Synthesis and Odour of 5-exo-Hydroxycamphene (Isonojigiku Alcohol)

The synthesis of the title compound is described. Hydroxylation of the endocyclic double bond of 2-acetyl-3,3-dimethylnorborn-5-ene furnished a mixture of nojigiku alcohol and the title compound. A shorter route leads from 2,5-norbornadiene solely to the desired camphoraceous smelling new hydroxy derivative to which the name isonojigiku alcohol is assigned.

Fluorine-Directed Nazarov Cyclizations 2: Regioselective Synthesis of 5-Trifluoromethyl-2-cyclopentenones

1-Trifluoromethylvinyl vinyl ketones are treated with trimethylsilyl trifluoromethanesulfonate in CH2Cl2-1,1,1,3,3,3-hexafluoro-2-propanol to afford 5-trifluoromethyl-2-cyclopentenones. Both acyclic and cyclic substrates furnish the corresponding cyclized products in good to excellent yields with defined placement of the endocyclic double bond due to the strong electronic effect exerted by the trifluoromethyl group.

Syntheses in the Isocamphane Series XLI [1]. Derivatives of Epoxyisocamphenilanic Acid, Epoxycamphene, and a New Access to 7-syn-Hydroxycamphene

The syntheses of the title compounds are described. Epoxidation of the endocyclic norbornene double bond leads to a series of epoxy derivatives of this class of terpenic compounds, which on account of their biological decomposability might turn out to be valuable microbiocides. Cleavage of the epoxide bridge of 5,6-epoxy-camphene opens a new access to the fragrance compound 7-syn-hydroxy-camphene via a rearrangement.

Photoextrusion of Molecular Nitrogen from Annulated 5-Alkylidene-4,5-dihydro-1H-tetrazoles: Annulated Iminoaziridines and the First Triplet Diazatrimethylenemethane

Deprotonation of the annulated tetrazolium salts 4, 6, 8, 10, and 12 with sodium or potassium hydride yields the alkylidenedihydrotetrazoles 5, 7, 9, 11, and 13, respectively. While 5a and b are unstable, even in solution at low temperatures, 7, 9, 11, and 13 form yellow oils that are distilled under high vacuum. − Irradiation of solutions of 7, 9, and 11 in [D8]toluene at −60°C yields, besides molecular nitrogen, annulated iminoaziridines that have an exocyclic CN double bond, i.e. 14, 16, and 18, respectively. In addition, an equal amount of the isomer 19 with the endocyclic CN double bond is formed from 11. On thermolysis, 14, 16, and 18 undergo [2 + 1] cycloreversion into methyl isocyanide and the cyclic imines 15, 17, and 20, respectively. By contrast, 19 rearranges thermally to yield 18. While the doubly bridged alkylidenedihydrotetrazole 13a affords only unidentified decomposition products on photolysis, its methyl homologue 13b is converted into the hexahydronaphthyridine 22 which is also formed on thermolysis. − Irradiation of 13b in a 2-methyltetrahydrofuran or butyronitrile matrix at 77 K yields a triplet diradical showing a four-line EPR spectrum centred at 3362 G and a half-field transition (at 1669 G) with a hyperfine structure. The zero-field splitting parameters |D-hc| = 0.031 cm−1 and |E-hc| = 0.0014 cm−1 are obtained by simulation of the EPR spectrum. The signal-carrier is assigned the diazatrimethylenemethane structure 23 on the basis of the close similarity between its EPR spectrum and those of trimethylenemethane (28) and tris(N-methylimino)methane (29). − Structural features are discussed that are responsible for the observed differences between the photochemical pathways.

Synthesis of alkylidene cyclopentenones. Enolization of 4-substituted cyclopent-4-ene-1,3-diones

The regioselective enolization of 4-substituted cyclopentene-1,3-diones 3a-e is investigated under basic and acidic conditions. Enols 1 and enolethers 6, 7 are formed with the simultaneous endocyclic double bond migration in the side chain.

Structure of 1,2,3,4,9,9-hexachloro-6,7-tetrahydro-l,4-methano-naphthalene: a facially differentiated, annulated 1,3-cyclohexadiene

The X-ray crystal structure of the title compound is reported. Crystal data: T = 100 K, monoclinic, P21/n, a = 8.2990(17), b = 13.2300(26), c = 12.0350(24) A, β = 93.676(30)°, V = 1318.7 (5) A3, and R = 0.0368. The methylene carbon atoms in the cyclohexadiene ring are disordered over two positions above and below the ring plane. The chlorine substituted endocyclic double bond deviates from planarity with an angle of 8.10(13)° toward the endo-face. The facially differentiated 1,3-cyclohexadiene moiety is only slightly pyramidalized, deviating 1.75(20)° also toward the endo-face of the tricyclic system.

Determinação da Estereoquímica Relativa de Pimaradienos Através de Produtos de Oxidação

Pimaradienes, including isopimaradienes, with an endocyclic double bond between C-9 and C-11 are uncommon compounds in nature. The diterpenoid pimar-9(11),15-dien-19-oic acid (1) was isolated from Mikania triangularis (Asteraceae) and the correct stereochemistry of 1was established by 1H and 13C NMR studies of several oxidative products, mainly epoxides, of this compound and its double bond isomers.

Regioselective dehydration of axial and equatorial tertiary alcohols with α-methyl group in the cyclohexane ring by Swern’s reagent

Swern’s reagent (a complex of oxalyl chloride with DMSO) was shown to dehydrate tertiary alcohols containing an α-methyl group in the cyclohexane ring. Dehydration of equatorial alcohols affords mixtures of isomeric compounds where isomers with an exocyclic double bond dominate, whereas isomers with an endocyclic double bond prevail in the products of dehydration of axial tertiary alcohols. Thus, Swern’s reagent can serve as a chemical test to determine the configuration of tertiary alcohols containing an α-methyl group in cyclohexane ring. The composition of the products of dehydration of these alcohols with Swern’s reagent is similar to that obtained by their dehydration with POCl3 in pyridine.

Synthesis of polycyclic cyclopropanecarboxylic acids and their esters based on catalytic cyclopropanation of 6,6-dimethylfulvene

Reactions of 6,6-dimethylfulvene with methyl diazoacetate in the presence of Cu compounds is accompanied by methoxycarbonylmethylenation of the endocyclic double bonds to give the corresponding mono- and diadducts in total yields of up to 85% with marked predominance ofanti-isomers. The subsequent cyclopropanation of monoadducts with diazomethane in the presence of Pd compounds also involves the endocyclic double bond and gives esters of tricyclo[4.1.0.0.2,4]heptanecarboxylic acid in high yields.

Synthesis and biological evaluation of strigol analogues modified in the enol ether part

Several analogues of strigol, which is a germination stimulant for seeds of the parasitic weeds Striga and Orobanche, have been prepared. Structural modifications are introduced in the vinyl ether part and include: i, analogues containing an endocyclic vinyl ether double bond, using tetronic acids as precursors; ii, geometrical isomerization of the vinyl ether double bond; and iii, analogues containing a methyl substituent on the vinyl ether double bond. During coupling reactions to give compounds belonging to the last-mentioned class, undesired C-alkylation occurs, which can be minimized by choosing the appropriate reaction conditions. Bioassays reveal that the analogues prepared exhibit considerable activity in the stimulation of seed germination of Striga hermonthica and Orobanche crenata.

Methyl 2,7,7-Trimethyl-4-(3-nitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate and 3-Acetyl-2,7,7-trimethyl-4-phenyl-1,4,5,6,7,8-hexahydro-5-quinolone

The 1,4-dihydropyridine (1,4-DHP) ring and the cyclohexanone ring adopt similar conformations in both the title compounds, methyl 2,7,7-trimethyl-4-(3-nitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate, C 20 H 22 N 2 O 5 , (I) and 3-acetyl-2,7,7-trimethyl-4-phenyl-1,4,5,6,7,8-hexahydro-5-quinolone, C 20 H 23 NO 2 , (II). The 1,4-DHP rings have boat conformations with the aryl group occupying the pseudo-axial position and orthogonal to the plane through the 1,4-DHP ring. The cyclohexanone ring has an intermediate half-chair/sofa form. In both compounds, the carboxyl group is coplanar to the endocyclic double bond as a consequence of π conjugation. The molecules are linked by N-H...O hydrogen bonds but the packing is different in each case. In compound (I) a hydrogen bond is formed between the N-H and the carboxyl group while in compound (II), a hydrogen bond is formed between the N-H and the O atom of the cyclohexanone ring.