Water → 5,5-dimethyltetrahydro-2H-pyran-2-one

To a solution of 2,2-dimethyl-pentanedioic acid (3.0 g, 19 mmol) is added K2CO3 (6.49 g, 47 mmol) and iodomethane (2.5 ml, 39 mmol) at room temperature. The mixture is stirred at room temperature for 18 hours. To the mixture, H2O is added and the solution is extracted with AcOEt. The organic layer is washed with H2O, saturated aqueous NaHCO3 and brine, and dried over MgSO4. Solvent is removed under reduced pressure to give 2,2-dimethyl-pentanedioic acid dimethyl ester (2.49 g, 70%); TLC (hexane/AcOEt, 3:1) Rf 0.50, 1H NMR (400 MHz, chloroform-d) δ ppm 1.19 (s, 6H), 1.88 (m, 2H), 2.29 (m, 2H), 3.67 (s, 6H). To a solution of 2,2-dimethyl-pentanedioic acid dimethyl ester (2.40 g, 12.8 mmol) in MeOH (15 ml) is added potassium hydroxide (0.788 g, 14.0 mmol). The mixture is stirred at room temperature for 16 hours and refluxed for 2 hours. The mixture is cooled to room temperature and concentrated under reduced pressure. To the obtained residue, 1M aqueous HCl (14 ml) is added and the solution is extracted with ether. The organic layer is washed with H2O, dried over Na2SO4, and concentrated under reduced pressure to give 2,2-dimethyl-pentanedioic acid 1-methyl ester (1.97 g, 88%); 1H NMR (400 MHz, chloroform-d) ppm 1.20 (s, 6H), 1.87-1.91 (m, 2H), 2.32-2.36 (m, 2H), 3.67 (s, 3H). To a suspension of 2,2-dimethyl-pentanedioic acid 1-methyl ester (1.00 g, 5.75 mmol) in THF (3 mL), 1M LiBHEt3 in THF (38.0 ml, 38.0 mmol) is added dropwise maintaining the temperature below 10° C. under nitrogen. The mixture is stirred at 10° C. for 1 hour. To the mixture, 50% AcOH (4.6 mL) and H2O are added. The solution is extracted with AcOEt, and the organic layer is washed with H2O, dried over MgSO4, and concentrated under reduced pressure to give 5-hydroxy-4,4-dimethyl-pentanoic acid (850 mg, quant.); 1H NMR (400 MHz, chloroform-d) ppm 1.06 (s, 6H), 1.70 (t, 2H), 2.56 (t, 2H), 3.98 (s, 2H). To a solution of 5-hydroxy-4,4-dimethyl-pentanoic acid (300 mg, 2.05 mmol) in DMF (5 ml), K2CO3 (369 mg, 2.87 mmol) and iodomethane (154 ul, 2.47 mmol) are added at room temperature. The mixture is stirred at room temperature for 15 hours. To the mixture, H2O is added and the solution is extracted with AcOEt. The organic layer is washed with H2O, and brine, and dried over MgSO4, and concentrated under reduced pressure. The residue is purified by silica gel column chromatography to give 5,5-dimethyl-tetrahydro-pyran-2-one (150 mg, 47%); TLC (hexane/AcOEt, 2:1) Rf 0.40, 1H NMR (400 MHz, chloroform-d) δ ppm 1.06 (s, 6H), 1.70 (t, 2H), 2.56 (t, 2H), 3.97 (s, 2H).