Water → 1-[2-(5-Bromo-4,6-dioxo-2,2-dimethyl-1,3-dioxan-5-yl)ethyl]-2-(benzoyl)pyrrole

Pyridinium bromide perbromide (11.51 g, 36 mmoles) in tetrahydrofuran (25 ml) was added dropwise at 0°-5° C. to a vigorously stirred suspension of the sodium salt of 1-[2-(4,6-dioxo-2,2-dimethyl-1,3-dioxan-5-yl)ethyl]-2-benzoylpyrrole (VI, prepared as described above, 13.5 g, 37.2 mole). The mixture was stirred for 1 hour at 0°-5° C. The mixture was then poured into water (600 ml) and extracted three times with diethyl ether (100 ml, then 2×50 ml). The organic phase was separated and washed with two 200 ml portions of water, dried over magnesium sulfate and evaporated to afford crystalline 1-[2-(5-bromo-4,6-dioxo-2,2-dimethyl-1,3-dioxan-5-yl)ethyl]-2-(benzoyl)pyrrole (VIIa). The product could be recrystallized from ethyl acetate/hexane to give material with the following properties: m.p. 89°-91° C. 1H NMR (CDCl3): delta 1.81 (s, 3H); 2.00 (s, 3H); 3.19 (t, 2H); 4.58 (t, 2H); 6.19 (dd, 1H); 6.71 (dd, 1H); 6.89 (dd, 1H); 7.4-7.55 (m, 3H); 7.78 (dd, 2H). 13C NMR (CDCl3): delta 26.8, 28.9, 39.7, 43.5, 45.8, 107.3, 123.5, 127.9, 129.2, 130.3, 131.4, 139.1, 163.0, 186.9.