... 4, p 531. (c) Comprehensive Heterocyclic Chemistry II; Katritzky ... The organic layer was dried over anhydrous Na2- SO4, and the solvent was removed in vacuo. ... on silica gel to afford compound 5a (97%) as white plates: mp 167-168 °C; 1H NMR δ 3.93 (s, 1H), 7.05 (t, J ) 3.9 Hz ...