Ammonium Chloride → Tetrahydro-2,6-dimethyl-4H-pyran-4-one

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A solution of 1.6M methyllithium in diethyl ether (20.9 mL, 33.4 mmol) was added to a stirred slurry of copper(I) iodide (4.25 g, 22.30 mmol) in diethyl ether (30 mL) at 0° C. and under nitrogen. The reaction was stirred at 0° C. for 20 min and then racemic 2-methyl-2H-pyran-4(3H)-one (1.25 g, 11.2 mmol) in diethyl ether (12.0 mL) was added over 10 min. The reaction was allowed to warm to RT and stirred 2 h. The reaction mixture was poured into sat NH4Cl (aq) and stirred 20 min. The solution was extracted with diethyl ether (4×60 mL) and the combined organics were washed with brine (˜80 mL), dried (MgSO4), filtered and concentrated to yield racemic (2R,6R)-2,6-dimethyldihydro-2H-pyran-4(3H)-one (Cap-2, step b) (1.34 g) as an orange oil. 1H NMR (400 MHz, CDCl3) δ ppm 4.28-4.39 (m, 2H), 2.55 (ddd, J=14.1, 4.8, 1.5 Hz, 2H), 2.24 (ddd, J=14.1, 6.5, 1.5 Hz, 2H), 1.28 (d, J=6.3 Hz, 6H).

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