V. A. Mironov

Thermal isomerization of 1-methylcyclopentadiene

1. The isomerization of 1-methyldicyelopentadiene (III) to 8-methyldicyclopentadiene (IV) at 145° takes place only by an intramolecular mechanism. 2. Depending on the reaction conditions, the diene synthesis can go by two different mechanisms: one-step and two-step.

Kinetics of the structural isomerization of the adduct of the reaction of 5-methyl-cyclopentadiene with maleic anhydride

1. The reaction of endo-exo-isomerization of the adduct of the condensation of cyclopentadienes with rnaleic anhydride is accomplished by dissociation of the adducts into kinetically independent addends, followed by their recombination. 2. Structural isomerization of the anhydride of 7-methylbiclyclo-(2,2,1)-heptene-2-dicarboxylic-5,6 acid, proceeding under conditions of endo-exo-isomerization, is a first order reaction. 3. The ratio of the products of structural isomerization remains constant at all stages of the conversion.

Configuration and thermal isomerization of adducts of substituted cyclopentadienes with maleic anhydride

1. The adducts of the methyl-substituted cyclopentadienes with maleic anhydride have an endo-configuration of the anhydride ring. 2. Structural isomerization is observed when the pure endo-anhydrides of 7-(I)-, 1-(II)-, and 2-(III)-methylbicyclo[2.2.1]-2-heptene-5, 6-dicarboxylic acids are heated in refluxing tetralin under the conditions of endo-exo isomerization. Each of the adducts (I)-(III) leads to the same mixture, containing compounds (II) and (IIa) and (III) and (IIIa) in a ratio of approximately 1 ∶ 2, and practically devoid of compounds (I) and (Ia). 3. Under the conditions of endo-exo isomerization there apparently occurs retrodienic decomposition of the adducts into the kinetically independent addenda, with their subsequent recombination.

Cyclic unsaturated compounds. 65. Cycloheptadienyl anions

1. The thermal isomerization of 1,3- and 1,4-cycloheptadiene is not observed up to 500°C. 2. In the presence of a strong base, 1,4-cycloheptadienes isomerize almost irreversibly to the corresponding 1,3-dienes; bases do not catalyze double-bond migration in the 1,3-cycloheptadiene series. 3. For the reaction of 1,3- and 1,4-cycloheptadienes with a strong base the formation of anions that can be alkylated occurs; these anions are not identical and, therefore, do not have the structure of a homocyclopentadienyl anion. 4. A correlation between the acidity of the hydrocarbons in the series eyclopentadiene-cyclohexadiene-cycloheptadiene and the enthalpy of activation for double-bond migration in the same series does not exist. Consequently, in this isomerization process the migrating hydrogen atom does not have a positive charge.

Unsaturated ring compounds

1. The hydrogenation kinetics of endo anhydrides of 7-syn-methyl-(II) and 7-anti-methyl-(III)-bicyclo [2,2,1]-hept-2-ene-5,6-dicarboxylic acids and the corresponding unsubstituted anhydride (I) have been in vestigated. Hydrogenation of the syn isomer (II) took place at approximately half the rate of the anti isomer (III) and the unsubstituted anhydride (I). The last two compounds gave approximately the same hydro genation rates. 2. A convenient method is proposed for determined the configuration of a substituent in position 7 of the bicyclo-[2,2,1]-heptene skeleton.

The syn-anti isomerism of adducts of 1,2,3,4,5-pentamethylcyclopentadiene with maleic anhydride

The dienic condensation of 1,2,3,4,5-pentamethylcyclopentadiene with maleic anhydride proceeds stereospecifically in relation to the configuration of the substituent in position 7 (the bridge) forming bicyclo[2.2.1] heptene derivatives: the ratio of the 7-syn-methyl- and 7-anti-methyl isomers (in relation to the double bond) corresponds to 3.5:1, respectively.

Kinetics of thermal isomerization of 1-methyldicyclopentadiene

1. The authors have studied the kinetics of reversible thermal isomerization of 1-methyldicyclopentadiene (I) to 8-methyldicyclopentadiene (II) in the range 120–150°. Such (I) ⇌ (II) conversions are first-order reactions. The rate constants of the forward and reverse reactions have been determined and the activation energies of (I) ⇌ (II) reactions calculated. 2. The rate of (I) ⇌ (II) isomerization is not changed by acids, bases, and Lewis acids and is independent of the nature of the surface of the flask and the presence of dissolved oxygen. 3. Reversible (I) ⇌ (II) thermal isomerization is evidently effected by an intramolecular biradical mechanism involving rupture of one diene-dienophil bond.

Thermal isomerization of 1,2,4,5, 5-pentamethylcyclopenta diene into 1,2,3,4, 5-pentamethyl-cyclopentadiene

1. At 425–500°, 1,2,4,5,5-pentamethylcyclopentadiene smoothly isomerizes into 1,2,3,4,5-pentamethyl-cyclopentadiene as a result of 1,3-migration of the methyl group in the cyclopentadiene ring. 2. The mechanism proposed for this isomerization is the combination of two consecutive acts of 1,2-migration of the methyl group.

Cyclic unsaturated compounds: Communication 18. On the mechanism of endo-exo-isomerization of the adduct of diene synthesis of cyclopentadiene with maleic anhydride

1. Together with the classical 1,2-elimination of the elements of water, 1,4-elimination takes place in the dehydration of the substituted 2-cyclopenten-1-ols, accompanied by migration of the double bond. 2. The data obtained make it possible to predict the cases where the synthesis of the substituted cyclopentadienes is accompanied by the formation of noticeable amounts of 3-methylene-1-cyclopentenes (dienes with a fixed transoid system of double bonds).

Synthesis and thermal tranformations of bicyclo-[3,1,0]-hexene-2 and bicyclo-[4,1,0]-heptene-3

1. Bicyclo-[3,1,0]-hexene-2 forms a mixture of cyclohexadiene-1,3 and cyclohexadiene-1,4 in an 8.9 ∶ 1 ratio, respectively, in almost quantitative yield at 400°. 2. Bicyclo-[4,l,0]-heptene-3 is thermally stable up to a temperature of 425°.