Ring opening of cycloalkanes

Adsorption modes and hydrogenolysis were also correlated with other metal-catalyzed reactions. Gault noticed striking similarities in product distributions of isomerization and ring opening of cycloalkanes. Kinetic and tracer studies provided useful data252 268 to arrive at the conclusion that a common surface intermediate is... 

Hydrogenative ring opening of cycloalkanes is also a well-studied area.16 252 253 289-292 Mainly cyclopropanes and cyclopentanes were studied, since three- and five-membered adsorbed carbocyclic species are believed to be intermediates in metal-catalyzed isomerization of alkanes (see Section 4.3.1). Ring-opening reactivity of different ring systems decreases in the order cyclopropane > cyclobutane > cyclopentane > cyclohexane.251 Cyclopropane and its substituted derivatives usually react below 100°C. 

Preparation of 2-Cycloalkenones and Cycloalkane-1,3-diones BY Iron(III) Chloride-Induced Ring Opening of 1-Trimethyi,-siLYLOxY- AND 1,2-Bis(trimethylsilyloxy)bicyclo[w.1.0]alkanes... 

Fig. 28 Nucleophilic ring opening of cyclic dimethylammonium ions [38], Free energies of activation relative to ring-size 6 against cycloalkane strain-energies. Energy units kcal mol"1. (Reproduced with permission from Di Vona et al., 1985)...

Exercise 12-17 Use the heats of combustion to liquid water given in Table 12-3 and appropriate bond energies to calculate AH° (vapor) for ring-opening of the cycloalkanes with bromine in the range n = 2 to n = 6 ... 

Acyloin condensation (2, 435-436). Japanese chemists3 have extended Bloomfield s procedure for ring enlargement of cycloalkane-1,2-dicarboxylie esters. Thus the esters (1) were treated with sodium in xylene at 110-120° in the presence of trimethylchlorosilane and the reaction mixture refluxed to ensure ring opening of the cyclobutenes (2) to 1,3-dienes (3). Acidic hydrolysis gave 1,2-diketones (4) in 71 -74% yields. These can be reduced to acyloins (5) by alkaline hydrolysis with triethyl phosphite (74-79%). 

Reduction of cycloalkane-condensed 2-phenyl-5,6-dihydro-4//-l,3-benzoxazines 144 with lithium aluminium hydride (LAH) afforded A -benzyl-substituted 2-(aminomethyl)cycloalkanols 145 in a reductive ring opening via the ring-chain tautomeric tetrahydro-l,3-oxazine intermediates. Catalytic reduction of 1,3-oxazines 144 under mild conditions in the presence of palladium-on-carbon catalyst similarly resulted in formation of the A -benzyl-1,3-amino alcohols 145. When the catalytic reduction was performed at elevated temperature at hydrogen pressure of 7.1 MPa, the N-unsubstituted 2-(aminomethyl)cycloalkanols 146 were formed in good yields (Scheme 22) <1998SC2303>. 

The reactivity of 1 in substitution reactions is markedly different from that of other cycloalkanes. An electrophilic substitution of 1 is followed by opening of the three-membered ring to a 2-propyl cation. Therefore, protonation of 1 as the simplest electrophilic attack has been extensively investigated, both experimentally218 220 and computationally221"223. 

Exercise 12-18 Investigate the thermodynamic feasibility of the following propagation steps for opening the rings of cycloalkanes with / = 2to/i = 6bya radical-chain mechanism ... 

The isomerization of cycloalkanes over SbF5-intercalated graphite can be achieved at room temperature without the usual ring opening and cracking reactions, which occur at higher temperatures and lower acidities.110 In the presence of excess hydrocarbon after several hours, the thermodynamic equilibrium is reached for the isomers. Interconversion between cyclohexane (20) and methylcyclopentane (21) yields the thermodynamic equilibrium mixture [Eq. (5.46)]. 

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