Sythesis of new benzopyranone mannich bases

ABSTRACT

Reaction of 7-hydroxy-5-methoxy-2-methyl-4-oxo-benzopyran-6- carboxaldehyde [1] with formaldehyde and piperidine [or morpholine] to give the corresponding 8-substituted piperidinomethyl or morpholinomethyl derivatives [compounds 2 and 3, respectively]. When formaldehyde and diethylamine were used, bis-[6-formyl-7-hydroxy-5- methoxy-2-methyl-4-oxo-benzopyran-8-yl]-methane [4] was formed. Reaction of 1 with hydroxylamine gave the aldoxime [5], which upon reaction with acetic anhydride gave the corresponding 7-acetyloxy-6- cyano-5-methoxy-2-methyl-4-oxo-benzopyran [6]. Mild hydrolysis of [6] with sodium hydroxide gave 6-cyano-7-hydroxy-5-methoxy-2-methyl- 4-oxo-benzopyran [7]. Reaction of 7 with piperidine and formaldehyde afforded the corresponding Mannich base [8]. Reaction of 1 with urea in ethanol gave the unexpected 5-ethoxy-7-hydroxy-2-methyl-4-oxo- benzopyran [10] which reacted with piperidine and formaldehyde to give the corresponding Mannich base [11]. Reaction of 1 with acetic anhydride gave 3-[7-hydroxy-5-methoxy-2-methyl-4- oxo-benzopyran-6- yl]-acrylic acid [12], while with acetic anhydride in the presence of anhydrous sodium acetate afforded 5-methoxy-8-methyl-2,6- dioxo- [2H,5H]-benzo-[3,2-b4,5-b']-dipyran [13]. The Mannich bases 3, 14 and the dimer 4 were obtained from compound 12. The dimer 4 could be also obtained by reaction of 1 with formaldehyde. Structures of the compounds prepared were determined by MS, 1H-NMR, IR and elemental analyses. The compounds prepared showed promising antimicrobial activity