An efficient and practical procedure for the synthesis of 2-benzyl- and 2-benzylidene-substituted benzo[b]thiazinones from easily available 2-iodophenylcinnamamides and potassium sulfide has been developed. In the presence of DBU, the reaction proceeds via electrophilic addition, followed by dehydrogenation and reduction to give 2-benzyl benzo[b]thiazinones. Furthermore, 2-benzylidenebenzo[b]thiazinones were obtained in moderate to good yields without the addition of DBU.