dimers 5a-c were prepared by the reaction of the corresponding α,β-unsaturated ketones 3a-c with Lawesson' Reagent (LR) in refluxing benzene. When these dimers were refluxed with LR in xylene, the 1,2-thiaphospholene-2-sulfides 7a-c were obtained. On the other hand, the thermolysis of the dimers 5a-c in the presence of acrylamide or dichloromaleic anhydride gave the corresponding cycloadducts of Diels-Alder type 8a-c, and 10a-c, respectively. The 3-carbamoyl thiapyran derivatives 8a-c showed good antimicrobial activity.