3-Acetyl-4-hydroxy substituted coumarins (II_a-c) were prepared. Their reactions with hydrazines in DMF gave the corresponding 4-hydroxy -(3-substituted pyrazolin-3-yl)coumarins (IV_a-f)  via the intermediate hydrazone (III). Their reaction with hydroxylamine hydrochloride gave the corresponding isoxazol-3-yl coumarin (VI_a-c) and (VII_a,b) via the oxime intermediate (V). Reaction of II with aromatic aldehydes gave the corresponding chalcone derivatives (VIII_a-k) which were reacted with hydrazines and hydroxyl amine hydrochloride and gave (IX_a)  and (X_a-c). Condensation of (II_a-c)with aromatic aldehydes, malononitrilein the presence ammonium acetate yielded the corresponding 3-cyano-4-aryl nictoinamido-6-yl-coumarin (XI_a-f). 4-Hydroxy comumarin (1_a-c) on treatment with POCl₃ in DMF give the corresponding 4-Chloro-3-formyl coumarin (XII_a-c) which on treatment with sod azide gave the corresponding 4-azido-3-formyl coumarin (XIII_a-c). 4-chloro-3-formyl coumarine (XII )on treatment with hydrazine gave pyrazolo coumarin derivatives (XIV_a-d) and on treatment with hydroxylamine hydrochloride gave 4-chloro-3-aldo oxime  coumarin derivatives (XV_a,b).On treatment of 4-azido-3-formyl coumarin with active methylene compounds such as malononitrile and ethyl cyanocetate derivatives gave (XVI_a-d) respectively. The antibacterial and antifungal activities of some compounds have been described.