Domino reactions with fluorinated five-membered heterocycles - Syntheses of trifluoromethyl substituted butenolides and γ-ketoacids

A new approach to trifluoromethyl substituted butenolides and their thioanalogues is described starting from 2-fluoro-3-trifluoromethylfurans and -thiophenes, respectively. The reaction sequence includes three steps - nucleophilic displacement reaction, Claisen, and finally Cope rearrangement - which can be run as domino reaction. A modification of the domino reaction (transesterification instead of Cope rearrangement) provides a concise access to α-trifluoromethyl-γ-ketoacids.