A two-step sequence for the synthesis of various 3,4-dihydro-2H-1,3-thiazines is presented. In the first step, 2H-1,3-thiazines were prepared by a new multicomponent reaction (MCR). Starting from β-chlorovinyl aldehydes, this MCR offers an efficient and facile access to 2,2-dialkyl- and 2-alkyl-2-aralkyl-5,6-diaryl-2H-1,3-thiazines. The potential of these products in subsequent reactions was verified by the conversion to 3,4-dihydro-2H-1,3-thiazine-containing bisamides, β-lactams, and methoxy amides.