[d][1, 3] thiazolo [3, 2-a] pyrimidin-10-ones (4a-g), 2-methyl-8-phenyl-5, 6, 7, 8, 11, 12-
hexahydro-10H-bemzo [6′, 7′] cyclohepta [4, 5] pyrimido [2, 1-b][1, 3]-thiazin-10-ones (6a-
g) and 2, 11-dimethyl-8-phenyl-5, 6, 7, 8, 10, 11-hexahydro-benzo [6, 7] cyclohepta [d][1, 3]
thiazolo [3, 2-a] pyrimidin-10-ones (8a-g) have been described. A number of compounds
show promising antimicrobial acitity.