Synthesis of α-(Trifluoromethyl)styrenes and 1,3-Di(trifluoromethyl)indanes via Electrophilic Activation of TMS Ethers of (Trifluoromethyl)benzyl Alcohols in Brønsted Acids

TMS ethers of CF3-benzyl alcohols (and their heterocyclic analogues) undergo elimination of TMSOH molecule with the formation of α-(trifluoromethyl)styrenes in yields of up to 90% under the action of strong Brønsted acids TfOH or H2SO4. Under the acidic conditions upon prolongation of the reaction, the α-(trifluoromethyl)styrenes are further dimerized into cis-/trans-1,3-di(trifluoromethyl)indanes in yields of up to 100%. Plausible reaction mechanisms of these electrophilic transformations including the intermediate formation of CF3-benzyl carbocations are discussed.