Cycloalkanes acid-catalyzed rearrangement

Cycloalkanes also undergo related acid-catalyzed rearrangements. Higher coordinate carbocations again play a key role in the mechanism as shown in the cyclohexane-methylcyclopentane rearrangement. ... 

The acid-catalyzed isomerization of cycloalkenes usually involves skeletal rearrangement if strong acids are used. The conditions and the catalysts are very similar to those for the isomerization of acyclic alkenes. Many alkylcyclohexenes undergo reversible isomerization to alkylcyclopentenes. In some cases the isomerization consists of shift of the double bond without ring contraction. Side reactions, in this case, involve hydrogen transfer (disproportionation) to yield cycloalkanes and aromatics. In the presence of activated alumina cyclohexene is converted to a mixture of 1-methyl- and 3-methyl-1-cyclopentene 103... 

An nnnsnal ring-contraction reaction occnrs on the acid-catalyzed interaction of trimeth-ylhydroqninone 144 with cycloalkane-1,2-diols (e.g. 145) to form the spiro componnds 146 (eqnation 67) . Besides two isomers of cyclohexane-1,2-diols 145, this rearrangement was also described for cyclopentane-, cycloheptane- and cyclooctane-1,2-diols . 

Acid-Catalyzed Reactions and Rearrangements of Alkanes, Cycloalkanes, and Related Compounds... 

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