Isopropanol → trans 4-(Bromomethyl)-2-isopropoxy-1,3-dioxolane

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To a solution of cis and trans 4-(bromomethyl)-2-methoxy-1,3-dioxolane (example 1) (5.37 g, 27.3 mmol) in benzene (100 mL) was added isopropanol (2.2 mL, 28.6 mmol, 1.05 eq.) and p-toluenesulfonic acid (pTSA, few crystals). The mixture was stirred for 24 hr at 88°-90° C. followed by addition of isopropanol (0.5 mL, 0.24 eq.). The mixture was stirred for further 24 hr at 90° C., cooled to room temperature and benzene was removed under reduced pressure. The crude material was obtained in quantitative yield consisting of a mixture of isopropoxy and methoxy orthoesters in a 9:1 ratio respectively. The ratio of cis and trans isomers was about 1:1. 1H NMR (300 MHz, CDCl3) δ: 1.21 (d, 6H, CH(CH3)2), 3.45 (m, 2H, CH2Br), 3.65 (m, 1H, CH(CH3)2), 3.92 (m, 1H, H-5a), 4.21 (m, 1H, H-5b), 4.42 and 4.55 (2m, 1H, H-4), 5.95 and 5.96 (2s, 1H, H-2).

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