Cyclopentene reaction

During the photocycloaddition of 88 with cyclopentene (Reaction 1), de of the major isomer 89 increased from 30% in nonpolar solvents up to 68 in a mixture of methanol and acetic acid. When prochiral enone 91 was irradia in the presence of a cyclopentene linked to the 8-phenylmenthol (Reaction the best selectivity was now obtained in nonpolar solvents. To explain this eff< it was proposed that the facial selectivity is high in every case and that diastereoselectivity depends on an s-cis s-trans ratio of the conjugated es influenced by hydrogen bonding [65]. Similar results were obtained with c... 

N° Catalyst composition Selectivity to cyclopentene, % Reaction rate ratio, Wolefine/Wdiene... 

The dicarboxylation of cyclic alkenes is a useful reaction. All-c.vo-methyl-7-oxabicyclo(2.2.1]heptane-2,3,5,6-tetracarboxylate (233) was prepared from the cyclic alkene 232 using Pd on carbon and CuCh in MeOH at room temperature with high diastereoselectivity[216]. The dicarbonylation of cyclopentene... 

Diacetates of 1,4-butenediol derivatives are useful for double allylation to give cyclic compounds. l,4-Diacetoxy-2-butene (126) reacts with the cyclohexanone enamine 125 to give bicyclo[4.3.1]decenone (127) and vinylbicy-clo[3.2.1]octanone (128)[85,86]. The reaction of the 3-ketoglutarate 130 with cij-cyclopentene-3,5-diacetate (129) affords the furan derivative 131 [87]. The C- and 0-allylations of ambident lithium [(phenylsulfonyl)methylene]nitronate (132) with 129 give isoxazoline-2-oxide 133, which is converted into c -3-hydroxy-4-cyanocyclopentene (134)[S8]. Similarly, chiral m-3-amino-4-hyd-roxycyclopentene was prepared by the cyclization of yV-tosylcarbamate[89]. 

The carbonylation of dehydrolinalyl methyl carbonate (35) at room temperature affords the cyclopentene derivative 37 formed by the ene reaction of... 

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. 

Step 2 of the mechanism m Figure 6 12 is a nucleophilic attack by Br at one of the carbons of the cyclic bromonium ion For reasons that will be explained m Chapter 8 reactions of this type normally take place via a transition state m which the nude ophile approaches carbon from the side opposite the bond that is to be broken Recall mg that the vicinal dibromide formed from cyclopentene is exclusively the trans stereoisomer we see that attack by Br from the side opposite the C—Br bond of the bromonium ion intermediate can give only trans 1 2 dibromocyclopentane m accordance with the experimental observations... 

Aldol reaction of campholenic aldehyde with propionic aldehyde yields the intermediate conjugated aldehyde, which can be selectively reduced to the saturated alcohol with a sandalwood odor. If the double bond in the cyclopentene ring is also reduced, the resulting product does not have a sandalwood odor (161). Reaction of campholenic aldehyde with -butyraldehyde followed by reduction of the aldehyde group gives the aHyUc alcohol known commercially by one manufacturer as Bacdanol [28219-61 -6] (82). 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

An interesting probe of reactivity was presented by Burton in his study of cycloadditions of l,2-disubstituted-3,3,4,4-tetrafluorocyclobutenes and 1,2-disub-stituted-3,3,4,4,5,5-hexaf1uorocyclopentenes with butadiene, 2-methylbutadiene, and 2,3-dimethylbutadiene [86], On the basis of the extent of their conversions to adducts, the relative reactivities of the cyclobutenes and of the cyclopentenes are as shown in equation 74. A typical reaction is shown in equation 75. 

Bifunctional molecules undergo intermolecular cyclizations with enamines through simple alkylations 112-114) and acylations 115). For example, the reaction between l-(N-pyrrolidino)cyclopentene and 1,4-diiodobutane produces, after hydrolysis, ketospirans 92 and 93 113). 

Adducts derived from cyclopropyl-TMM reactions are versatile synthetic intermediates. Alkylidenecyclopropanes have been proven useful in further Pd-cata-lyzed transformations [4], On the other hand, vinylcyclopropanes can undergo smooth thermal ring-expansion to cyclopentenes. Thus, a total synthesis of 11-hy-droxyjasionone (27) was achieved with the cyclopropyl-TMM cycloaddition as the crucial step, and the thermal rearrangement of the initial adduct (28) as an entry to the bicyclo[6.3.0]undecyl compound (29), a key intermediate in the synthetic sequence (Scheme 2.9) [19]. 

Some alicyclic 1,2-diamine derivatives have recently been shown to have interesting CNS properties. For example, eclanamine (34) is an antidepressant with a rapid onset of action. The reasons for its potency are not as yet clear but pharmacologists note that the drug desensitizes adrenergic alpha-2 receptors and antagonizes the actions of clonidine. The synthesis of eclanamine starts with attack of cyclopentene oxide (30) by dimethylamine (to give 31). This product is converted to the mesylate by reaction with sodium hydride followed by mesyl chloride. Attack of... 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

A dry 5(X)-mI flask equipped with a thermometer, pressure-equalizing dropping funnel, and magnetic stirrer is flushed with nitrogen and then maintained under a static pressure of the gas. The flask is charged with 50 ml of tetrahydrofuran and 13.3 ml (0.15 mole) of cyclopentene, and then is cooled in an ice bath. Conversion to tricyclo-pentylborane is achieved by dropwise addition of 25 ml of a 1 M solution of diborane (0.15 mole of hydride see Chapter 4, Section 1 for preparation) in tetrahydrofuran. The solution is stirred for 1 hour at 25° and again cooled in an ice bath, and 25 ml of dry t-butyl alcohol is added, followed by 5.5 ml (0.05 mole) of ethyl bromoacetate. Potassium t-butoxide in /-butyl alcohol (50 ml of a 1 M solution) is added over a period of 10 minutes. There is an immediate precipitation of potassium bromide. The reaction mixture is filtered from the potassium bromide and distilled. Ethyl cyclopentylacetate, bp 101730 mm, 1.4398, is obtained in about 75% yield. Similarly, the reaction can be applied to a variety of olefins including 2-butene, cyclohexene, and norbornene. 

When the halogenation reaction is carried out on a cycloalkene, such as cyclopentene, only the trews stereoisomer of the dihalide addition product is formed rather than the mixture of cis and trans isomers that might have been expected if a planar carbocation intermediate were involved. We say that the reaction occurs with anti stereochemistry, meaning that the two bromine atoms come from opposite faces of the double bond—one from the top face and one from the bottom face. 

How does the formation of a bromonium ion account for the observed anti stereochemistry of addition to cyclopentene If a bromonium ion is formed as an intermediate, we can imagine that the large bromine atom might "shield" one side of the molecule. Reaction with Br ion in the second step could then occur only from the opposite, unshielded side to give trans product. 

Problem 7.5 What product would you expect from the reaction of cyclopentene with NBS and water Show the stereochemistry. 

Vinyl-substituted cyclopropanes undergo thermal rearrangement to yield cyclopentenes. Propose a mechanism for the reaction, and identify the pericyclic process involved. 

The reaction of benzopentathiepin with alkenes [(fl-but- -ene, ( )-hex-3-ene, cyclopentene or cyclohexene] in the presence of the boron trifluoride-diethyl ether complex results in the formation of 3,4-dihydro-l,2,5-benzotrithiepins, e.g. formation of 3.407... 

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