Single-crystal X-ray diffraction analysis and mechanistic implications of (2 <i>R</i> *,3 <i>R</i> *)-2-(2-phenoxyethyl)tetrahydrofuran-3-yl acetate

Our laboratory recently explored a highly stereospecific rearrangement of epoxides into tetrahydrofurans. To unambiguously determine the stereochemical outcome of this rearrangement, single crystals of one of the products, (2R*,3R*)-2-(2-phenoxyethyl)tetrahydrofuran-3-yl acetate, C₁₄H₁₈O₄, were grown and analyzed. Based on the crystal structure data, we were able to show that the contiguous stereocenters of this molecule are in a syn configuration, and we now suggest with confidence a plausible mechanism for the rearrangement reaction. The syn configuration of the ring may also account for the inability of most members of this class to crystallize, as it imparts a kink in the structure reminiscent of low-melting unsaturated fatty acids.