The general procedure for the synthesis of 4-methyltetrahydropyran-4-carboxylic acid from methyl 4-methyl-tetrahydro-2H-pyran-4-carboxylate was as follows: to a solution of methyl 4-methyltetrahydro-2H-pyran-4-carboxylate (5.00 g, 31.6 mmol) in a 1:1:1 mixed solvent of dioxane/water/methanol (60 mL), lithium hydroxide hydrate (5.31 g, 126 mmol) and the reaction mixture was stirred at room temperature overnight. Upon completion of the reaction, the mixture was partially concentrated and subsequently diluted with water and ethyl acetate (EtOAc) and acidified with 6 M hydrochloric acid to pH=1. The organic and aqueous layers were separated and the aqueous layer was extracted with additional ethyl acetate (50 mL). All organic layers were combined, washed with saturated brine, dried over anhydrous sodium sulfate and concentrated to dryness to afford 4-methyltetrahydro-2H-pyran-4-carboxylic acid (4.61 g, 100% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 12.29 (s, 1H), 3.65 (dt, J=11.8,4.3 Hz, 2H), 3.33-3.32 (m, 2H), 1.87-1.86 (m, 2H), 1.35 (ddd, J=13.5,9.9,4.1 Hz, 2H). 1.13 (s, 3H).
