Mechanism of intramolecular cycloalkylation of 3-methyl-3-phenyl-1-butanol in the presence of D3PO4

The intramolecular cycloalkylation of isomeric 2-methyl-4-phenyl-2-butanol and 3-methyl-3-phenyl-1-butanol in D3PO4 is accompanied by hydrogen exchange with the formation of deuterated 1,1-dimethylindane. The distribution of the deuterium in the polymethylene ring shows that the reaction of the first alcohol takes place as a result of C5-cyclization of the γ-phenylalkyl cation, whereas the reaction of the second alcohol takes place by direct C5-cyclization and by cyclization of the γ-phenylalkyl cations formed as a result of 1,2- and 1,3-transfers of the phenyl group