Reaction Steps
A solution of Cl2 in CHCl3 (freed of inhibitor by passing through a silica gel column) was prepared by adding concd HCl to stirred MnO2 and bubbling the resulting effluent through inhibitor free CHCl3. The resulting green solution was passed through a small silica gel column prior to use to remove H2O. The Cl2 concentration was not determined. To a stirred solution of 5,8-dihydro-2-methoxy-5-methylnaphthalene-1,4-dione (950 mg, 4.65 mmol) in inhibitor free CHCl3 (20 mL) the above described Cl2 solution was added in portions with stirring. The reaction was monitored by TLC (CHCl3). When the analysis indicated the total consumption of the starting material, the solvent was removed from the reaction mixture in vacuo to give a yellow oil. This was subject to column chromatography (silica gel, 2.5×25 cm column, 50% hexanes/50% CHCl3 elution). Some impurities eluted initially. The desired product eluted next as a yellow band followed closely by impurities. Solvent removal from the purest fractions yielded a yellow oil (293 mg, 80-90% pure by TLC and 1H NMR). The mixed product fraction was stripped of solvent in vacuo and the resulting yellow oil re-chromatographed in a manner similar to that described above (employed 2.5×50 cm column). Solvent removal from the purest fractions yielded an additional portion of a yellow oil (132 mg, 80-90% pure by TLC and 1H NMR; total yield 425 mg, 33%); 1H NMR (CDCl3) δ1.53 (d, J=7.5 Hz, 3H), 2.98 (m, 1H), 3.28 (m, 2H), 3.82 (s, 3H), 4.22 (m, 1H), 4.39 (dd, J1 =5.1 Hz, J2 =9.9 Hz, 1H), 6.92 (s, 1H); IR (KBr) 3325 (w), 3255 (w), 3077 (w), 2981 (m), 2940 (m), 2879 (w), 2848 (m), 1677 (s), 1674 (s), 1651 (s), 1637 (s), 1634 (s), 1609 (s), 1455 (m), 1412 (w), 1387 (w), 1372 (w), 1347 (m), 1304 (m), 1289 (m), 1226 (s), 1185 (w), 1147 (m), 1118 (m), 1089 (w), 1056 (w), 1044 (m), 1017 (m), 978 (m), 954 (m), 941 (w), 918 (m), 896 (w), 850 (m), 805 (m), 793 (m), 786 (m), 763 (m), 712 (m), 687 (m), 654 (m) cm-1.
