The 4-benzyloxy-1-oxaspiro-[4.6]-undec-3-en-2-one (C17H20O3) was prepared through a domino reaction from benzyl α-hydroxycycloheptanecarboxylate and the cumulated ylide Ph3P=C=C=O by: (i) addition and (ii) intramolecular Wittig Olefination reaction. The reaction was carried out using anhydrous toluene as solvent under an argon atmosphere in a Schlenk flask. Molecular characterization was performed by Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, (1H,13C – mono and bidimensional) nuclear magnetic resonance spectroscopy; crystallographic characterization was completed by X-ray diffraction of polycrystalline samples (XRPD). The title compound crystallized in a monoclinical system and unit-cell parameters are reported [a = 13.207(3) Å, b = 5.972(1) Å, c = 19.719(4) Å, β = 105.67(2)°, unit-cell volume V = 1497.5 (4) Å3, Z = 4]. All of the measured lines were indexed with the P21/n (No. 14) space group.