Cyclohexenes trans

Both cis and tran -cyclohexene have been synthesized, but only one of them can be isolated. Electrophilic addition of ROH to one isomer occurs spontaneously, while addition to the other isomer occurs only in the presence of a strong acid, such as sulfuric acid. Calculate the energy of protonation for each isomer cyclohexene protonated cyclohexene, trans-cyclohexene protonated trans-cyclohexene), and identify the more reactive isomer. Also examine electrostatic potential maps. Suggest an explanation to account for both the reactivity difference and the structural changes. (See also Chapter 7, Problem 5.)... 

Methyl-buten-(3)-in-(l) liefert mit Dicyclohexyl-boran und Deuterolyse 3-Methyl-1 -deutero-butadien-(trans-1,3) (92% d.Th.) bzw. 1-Athinyl-cyclohexen trans-2-Deute-ro-1 -[cyclohexen-(l)-yl]-athylen (87% d.Th.)3. Die Reduktionen sind auch mit [2,3-Di-methyl-butyl-(2)]-boran durchfiihrbar. 

Cyclohexene, ds-3- (3-4-dimethoxy phenyl)-4-(trans-3-4-dimethoxy styryl) Rh 50.6" ° Cyclohexene, trans-3-(2-4-5-trimethoxy phenyl)-4-(trans-3-4-dimethoxy styryl) Rh 13.9" ° ... 

C1I2)4- 4-CH, Cyclohexen trans-2-(4-Methyl-anilino) -1-phenylthio-cyclohexan 80... 

NO, Cyclohexen trans-2- (4-Nitro-anilino j-l -phenylthio-cyclohexan 94... 

ACETOXY-4-(DICARBOMETHOXYMETHYL)-2-CYCLOHEXENE, cis PROPANEDIOIC ACID, [4-(ACETYLOXY)-2-CYCLOHEXEN-1-YL]-, DIMETHYL ESTER, cis- (11) (82736-52-5), 69, 38 1 -ACETOXY-4-(DICARBOMETHOXYMETHYL)-2-CYCLOHEXENE, trans PROPANEDIOIC ACID, [4-(ACETYLOXY)-2-CYCLOHEXEN-1-YL]-, DIMETHYL ESTER, trans- (11) (82736-53-6), 69, 38 1-ACETOXY-4-DIETHYLAMINO-2-BUTENE 2-BUTEN-1 -OL, 4-(DIETHYLAMINO)-, ACETATE (82736-47-8), 67, 105... 

Cycloadditions in which 1,2-dithietes acted formally as dienes are among the most typical reactions of 1,2-dithietes. The dithiete 144 is highly reactive and capable of reactions even with simple alkenes and alkynes (60JA1515 61JA3434,61JA3438). Thus, 144 reacted with acetylene to form 191 and 192 with the initial formation of 193, and with tetramethylethylene to give 194. Other [4 + 2] cycloadditions of 144 involved those with ethylene, cyclohexene, trans-stilbene, ethyl vinyl ether, butyl vinyl sulfide, 3-hexyne, and DMAD. 

Cyclohexadiene oxide (13) is even more reactive toward acid-catalyzed hydrolysis than cyclopentadiene oxide (12), and comparable yields of both 3-cyclohexene-trans-... 

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

In MeOH, l,4-dimethoxy-2-cyclohexene (379) is obtainejl from 1,3-cydo-hexadiene[315]. Acetoxylation and the intramolecular alkoxylation took place in the synthesis of the naturally occurring tetrahydrofuran derivative 380 and is another example of the selective introduction of different nucleo-philes[316]. In intramolecular 1,4-oxyacetoxylation to form the fused tetrahy-drofurans and tetrahydropyrans 381, cis addition takes place in the presence of a catalytic amount of LiCI, whereas the trans product is obtained in its absence[317]. The stereocontrolled oxaspirocyclization proceeds to afford the Irons product 382 in the presence of Li2C03 and the cis product in the presence of LiCl[ 318,319]. 

Such a structure implies that there would be a barrier to rotation about the C(2)—C(3) bond and would explain why the s-trans and s-cis conformers lead to different excited states. Another result that can be explained in terms of the two noninterconverting excited states is the dependence of the ratio of [2 + 2] and [2 + 4] addition products on sensitizer energy. The s-Z geometry is suitable for cyclohexene formation, but the s-E is not. The excitation energy for the s-Z state is slightly lower than that for the s-E. With low-energy sensitizers, therefore, the s-Z excited state is formed preferentially, and the ratio of cyclohexene to cyclobutane product increases. ... 

Benzene-sensitized photolysis of methyl 3-cyclohexene-1-carboxylate in acetic acid leads to addition of acetic acid to the double bond. Only the trans adducts are formed. What factor(s) is (are) responsible for the reaction stereochemistry Which of the two possible addition products, A or B, do you expect to be the major product ... 

Reagent combinations lor additions of the halogen fluorides to cyclohexene to form trans 1 halo 2 fluorocyclohcxane (equation 1) are shown in Table 1... 

Johnson and Whitehead have further shown that the reductive elimination of the pyrrolidine group from the pyrrolidine enamine of 2,4-dimethyl-cyclohexanone (16), which involved treating it with a mixture of lithium aluminum hydride and aluminum chloride (9), gave the trans isomer of 3,5-dimethyl-/l -cyclohexene (17) which on subsequent hydrogenation on a platinum catalyst led to the // onr-3,5-dimethylcyclohexane (18). 

Treatment of the piperidine 74, obtainable from an aminonitrile such as 73, under N-methylation conditions leads to the dimethylamino derivative 75. The carbobenzoxy protecting group is then removed by catalytic hydrogenation. Reaction of the resulting secondary amine 76 with cyclohexene oxide leads to the alkylated trans aminoalcohol. There is thus obtained the anti-arrhythmic agent transcainide (77) [18]. 

Chemical Name (2S-trans)-7-chloro-2, 4,6-trimethoxy-6 -methylspiro[benzofuran-2(3H),-1 -[2] cyclohexene] -3,4 -dione... 

Isomer (H) 4-phenyl-3-trans-dimethylamino-4-trans-carbethoxy-A -cyclohexene hydrochloride, [ethyl-trans-3-(dimethylamino)-4-phenyl-1-cyclohexene-4-carboxylate hydrochloride], MP 159°C (the free base boils at 95.5° to 96°C at 0.01 mm pressure), 22.2% yield. 

Cvclodecene can exist in both cis and trans forms, but cyclohexene cannot. Explain. (Making molecular models is helpful.)... 

The Diels-Alder cycloaddition reaction (Section 14.4) is a pericvclic process that takes place between a diene (four tt electrons) and a dienophile (two tr electrons) to yield a cyclohexene product. Many thousands of examples of Diels-Alder reactions are known. They often take place easily at room temperature or slightly above, and they are stereospecific with respect to substituents. For example, room-temperature reaction between 1,3-butadiene and diethyl maleate (cis) yields exclusively the cis-disubstituted cyclohexene product. A similar reaction between 1,3-butadiene and diethyl fumarate (trans) yields exclusively the trans-disubstituted product. 

An alternative method for generating enriched 1,2-diols from meso-epoxides consists of asymmetric copolymerization with carbon dioxide. Nozaki demonstrated that a zinc complex formed in situ from diethylzinc and diphenylprolinol catalyzed the copolymerization with cyclohexene oxide in high yield. Alkaline hydrolysis of the isotactic polymer then liberated the trans diol in 94% yield and 70% ee (Scheme 7.20) [40]. Coates later found that other zinc complexes such as 12 are also effective in forming isotactic polymers [41-42]. 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

A portion of the product was heated to reflux with methanolic sodium methoxide to convert it into the thermodynamic mixture of trans- (ca. 65%) and cis- (ca. 35%) isomers. Small amounts of the isomers were collected by preparative gas chromatography using an 8 mm. by 1.7 m. column containing 15% Carbowax 20M on Chromosorb W, and each isomer exhibited the expected spectral and analytical properties. The same thermodynamic mixture of isomers was prepared independently by lithium-ammonia reduction5 of 2-allyl-3-methyl-cyclohex-2-enone [2-Cyclohexen-l-one, 3-methyl-2-(2-propcnyl)-],6 followed by equilibration with methanolic sodium methoxide. 

Conversion of epoxides into /3-hydroxy isocyanides—preparation of trans-2-isocyanocyclohexanol, using TMSCN to open cyclohexene oxide with trans stereochemistry, followed by KF/MeOH cleavage of the intermediate silyl ether. 

---