The title compound, C26H25NO2, is one of the two main products formed when an inseparable mixture of the diastereomeric (2R, 3S)- and (2S, 3S)-3-triphenylmethylaminooxinan-2-ylacetic acids is treated with N,N'-dicyclohexylcarbodiimide and 1-hydroxybenzotriazole. The crystal structure determination unambiguously shows that this compound has the tetrahydropyranyl and pyrrolidonyl rings fused in the trans configuration.