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n-Butyl lithium (18 mL, of a 1.6 M solution in hexane, 28 mmol) was added to a solution of 3-methyl-3tetrahydropyranyloxy-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−): 2209, 1741, 1689. MS-APCI calculated for C14H20O5 [M]− 268.13. found 267.96.

1. temperaturecooled to −78° C.
2. extractionThe aqueous layer was extracted with of Et2O (3×25 mL)
3. dry with materialThe organics were dried over MgSO4
4. customthe solvent was removed under reduced pressure
5. customthe resulting pale yellow oil was purified by chromatography (silica gel, hexane/AcOEt 90:10)