An efficient cyclocondensation reactions, antimicrobial activity and molecular orbital calculations of α-benzopyrone derivatives

An efficient synthesis of 4,6,8-trimethyl-2-oxo-2H-chromene-3-carbonitrile (2) via Claisen condensation of 3,5-dimethyl-2-hydroxyacetophenone with ethyl cyanoacetate in the presence of sodium metal is reported. Cyclocondensation reactions of compound (2) with ethyl acetate or with ethyl cyanoacetate in the presence of ethoxide gave sodium salt of 7-amino-9-hydroxy-2,4-dimethyl-6H-benzo[c]chromen-6-one derivatives (3) and (4) respectively, which upon neutralization with 10 % hydrochloric acid gave 7-amino-9-hydroxy-2,4-dimethyl-6H-benzo[c]chromen-6-one (5). Hydrolysis of compound (2) with ethanolic sodium hydroxide solution gave 4,6,8-trimethyl-2-oxo-2H-chromene-3-carboxylic acid (6). Treatment of compound (2) with Vilsmier reagent using excess POCl3 gave 4-(chloro(formyl)methyl-6,8-dimethyl-2-oxo-2H-chromene-3-carbonitrile (7). Also, conden-sation of compound (2) with DMF-DMA in xylene or with POCl3/DMF in pyridine gave the same product 4-((E)-2-(dimethylamino)vinyl)-6,8-dimethyl-2-oxo-2H-chromene-3-carbo-nitrile (8). The cyclocondensation reactions of compound (8) with hydroxylamine hydrochloride, urea, and with hydrazinecarbodithioic acid gave 3,4-dihydro-3-hydroxy-4-imino-7,9-dimethylchromeno[3,4-c]pyridin-5-one (9), 4-imino-7,9-dimethyl-5-oxo-4H-chro-meno[3,4-c]pyridine-3(5H)-carboxamide (10) and 3-amino-3,4-dihydro-4-imino-7,9-dimethyl chromeno[3,4-c]pyridin-5-one (11), respectively. Also, acid hydrolysis of compound (8) gave 7,9-dimethyl-3H-chromeno[3,4-c]pyridine-4,5-dione (12). Structures of the products were established on the basis of elemental analysis, IR, 1H and 13C NMR, mass spectra and semi-empirical AM1-MO calculations. The antimicrobial activities of the synthesized products were also studied.