An efficient synthesis of 1,5-Benzothiazepines via Michael addition of corresponding (E)-1-(2-hydroxyphenyl)-3-(4-(phenylthio)phenyl)prop-2-en-1-one is described under ultrasound irradiation. A series of novel 2-((E)-2,3-dihydro-2-(4-(phenylthio)phenyl)benzo[b][1,4]thiazepin-4-yl)phenol derivatives was confirmed on the basis of $^1H$ NMR, Mass, IR spectral data and Elemental analysis. The synthesized compounds were evaluated for their antimicrobial activities. Most of the compounds were found to be comparable potent than the reference standard drugs. Utilization of ultrasound irradiation, simple reaction conditions, isolation, and purification makes this manipulation very interesting from an economic and environmental perspective.