4.2.7 Synthesis of cis-2-phenyl-1,3-dioxan-5-ol (18): In a reaction flask fitted with a Dean-Stark splitter, a solution of freshly distilled benzaldehyde (48 mL, 50 g, 0.47 mol) and glycerol (44 mL, 55 g, 0.60 mol) in toluene (69 mL) was added, followed by dropwise addition of concentrated sulfuric acid (3 drops). The reaction mixture was heated to reflux until the water was completely separated (8.5 mL of water was collected). After completion of the reaction, the mixture was cooled to room temperature and the solvent was removed by distillation under reduced pressure. The white solid obtained was recrystallized by isopropyl ether/petroleum ether solvent mixture. The precipitate was collected and analyzed by fast column chromatography (column size: = 6 cm, h = 15 cm, eluent volume V = 50 mL, cyclohexane/ethyl acetate = 2:1, Rf = 0.16) for further purification to afford the target product 18 as a colorless solid (42.6 g, 0.24 mol, 50% yield). Melting point (Mp) = 81 °C; 1H NMR (DMSO-d6) δ: 3.48-3.52 (m, 1H, OCH2CHOH), 3.91-3.97 (m, 2H, OCH2CHOH), 4.01-4.07 (m, 2H, OCH2CHOH), 4.99 (d, J = 4.8 Hz, 1H, OH), 5.53 (s , 1H, CHPh), 7.33-7.40 (m, 3H, benzene ring 3',4',5'-H), 7.42-7.47 (m, 2H, benzene ring 2',6'-H); 13C NMR (DMSO-d6) δ: 62.4 (OCH2CHOH), 71.4 (2C, OCH2CHOH), 100.2 (CHPh) 126.2 (2C, benzene ring C-2', C-6'), 127.9 (2C, benzene ring C-3', C-5'), 128.5 (benzene ring C-4'), 138.9 (benzene ring C-1'); IR (pure sample, cm-1 ): 3271, 2916, 2851, 1450, 1385, 1339, 1277, 1153, 1084, 995, 976, 806, 741, 694; HRMS (m/z): [M + H]+ calculated value C10H13O3, 181.0859; measured value, 181.0878; HPLC (Method 1): tR = 11.7 min, purity 95.4%.
