n-Butyl lithium (18 mL, of a 1.6 M solution in hexane, 28 mmol) was added to a solution of 3-methyl-3-tetrahydropyranyloxy-butyne (3.3 g, 19 mmol) in Et2O, previously cooled at 0° C. The resulting solution was stirred for 30 min at 0° C., then cooled to −78° C. and diethyl oxalate (4.3 mL, 29.4 mmol) was added. The reaction was followed by TLC (hexane/AcOEt 90:10). After ca. 2 h the reaction mixture was poured in a cold aqueous solution of NH4Cl. The aqueous layer was extracted with of Et2O (3 25 mL). The organics were dried over MgSO4, the solvent was removed under reduced pressure and the resulting pale yellow oil was purified by chromatography (silica gel, hexane/AcOEt 90:10) to give ethyl 5-methyl-2-oxo-5-(tetrahydro-2H-pyran-2-yloxy)hex-3-ynoate (2) as a pale yellow liquid. Yield: 2.04 g (40%). 1H-NMR spectrum in CDCl3 (ppm): 5.10 (m, 1H), 4.38 (q, 2H), 4.36 (m, 2H), 3.96 (m, 2H), 3.54 (m, 2H), 1.85 (m, 2H), 1.75 (m, 2H), 1.64 (s, 3H), 1.59 (s, 3H), 1.40 (t, 3H). 13C-NMR spectrum in CDCl3 (ppm): 169.3, 158.7, 101.4, 96.2, 81.6, 70.5, 63.1, 31.5, 29.2, 28.9, 25.2, 19.9, 13.8, 13.8. Selected IR (neat, cm−1): 2209, 1741, 1689. MS-APCI calculated for C14H20O5 [M]− 268.13; found 267.96.
