General procedure for the synthesis of 2,2-dimethyl-5-ethoxycarbonyl-1,3-dioxane-5,5-dicarboxylic acid from diethyl 2,2-dimethyl-1,3-dioxane-5,5-dicarboxylate: a mixture of diethyl 2,2-dimethyl-1,3-dioxane-5,5-dicarboxylate (385 g, 1.5 mol), sodium chloride (105 g, 1.8 mol), water (58 g , 3.2 mol) and dimethyl sulfoxide (1500 mL) were refluxed for 20 hours. After completion of the reaction, the solution was cooled to room temperature, saturated sodium chloride solution (750 mL) was added, and the product was extracted with ether (4 x 600 mL). The combined organic extracts were washed with brine (2 x 150 mL) and dried with anhydrous sodium sulfate. After removal of the solvent by evaporation, the residual oil was purified by distillation to afford 2,2-dimethyl-5-ethoxycarbonyl-1,3-dioxane (220 g, 78% yield) as a colorless liquid.1H NMR (700 MHz, CDCl3, 300K): δ= 4.16 (q, J = 7.3 Hz, 2H), 4.01-4.08 (m, 4H), 2.77- 2.81 (m, 1H), 1.43 (s, 3H), 1.40 (s, 3H), 1.26 (t, J = 7.3Hz, 3H).
