A solution of 600 mg of 10k in 8 ml of acetic anhydride and 1g of anhydrous sodium acetate was heated under N2 for 45 min at 100° C. The reaction mixture was cooled and 20 ml of water was added and the mixture was stirred for another 1 hr at ambient temperature. The reaction mixture was then treated with cold conc. aq. NH4OH to make it slightly basic and the product was extracted with ethyl acetate. The crude material thus isolated was purified by chromatography over silica gel, using a gradient of heptane/acetone as eluent. The product isolated, was triturated with diisopropyl ether and provided 350 mg of white crystalline 10l. Mp: 233-234° C., Rf 0.55 (toluene/ethylactetate 1/1). NMR (CDCl3) δ 1.25-1.45 (bs, 15, tertC4H9+isoC3H7), 3.87 (s, 3, OCH3), 4.65 (bm, 1, isoC3H7), 6.72 (bs, 1, Ar—H), 6.93 (bm, 1, thiophene-H), 7.15 (bm, 2, thiophene-H+Ar—H), 7.43 (bm, 1, thiophene-H).
