Brominated CF3-allyl alcohols as multicentered electrophiles in TfOH promoted reactions with arenes

Abstract

Superacidic activation of CF₃-substituted allyl alcohols, bearing one or two bromine atoms at the CC double bond, with TfOH was studied. These brominated alcohols were found to behave as highly reactive multicentered electrophiles. The obtained cationic intermediates were studied by means of NMR and DFT calculations. The protonation of dibromo derivatives with TfOH resulted in cyclization to form trifluoromethylated 1H-indenes and/or indan-1-ones in yields up to 90%. The reaction of dibromosubstituted CF₃-allyl alcohols with arenes in the presence of TfOH gave rise to either CF₃-alkenes (formal substitution of hydroxyl with an aryl group) or CF₃-indenes, depending on the nucleophilicity and bulkiness of the starting arenes. The reaction of monobrominated CF₃-substituted allyl alcohols with arenes in TfOH afforded two regioisomeric CF₃-alkenes, as a result of arylation of both terminal carbons of the allyl system, in yields up to 95%. The obtained brominated CF₃-alkenes can be converted efficiently into trifluoromethylated allenes by treatment with KOH in ethanol in yields up to 92%.