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.