Atropisomerism of a monosubstituted perfluoro[2.2]paracyclophane. A combined synthetic, kinetic, spectroscopic and computational study

Abstract

The product of S_NAr addition of the enolate of ethyl acetoacetate to perfluoro[2.2]para-cyclophane exists entirely as its enol tautomer 5. This enol exhibits two NMR signals for its enolic proton, and these signals were shown to derive from the presence of two, equal energy conformations that were observable as distinct, stable conformations at room temperature, but which when heated, interconverted with an energy barrier of 23.5 kcal mol⁻¹. These atropisomers were characterized by NMR, with details of this analysis being provided. Computational work corroborated the NMR conclusions, and provided additional insight into all structural, thermodynamic and kinetic results. Enol product 5 was cyclized, under basic conditions, to form a benzofuran product 6. Its structure was confirmed by NMR, with further structural and mechanistic insights being provided by calculations.