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The thionation and cyclization of N-(ω-halogenoalkyl)-substituted amides (and related compounds) with Lawesson's reagent (LR=2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide) has been investigated. Treatment of the amides 1 with LR gave the corresponding thioamides 2 in moderate to good yields (Table). The latter, upon treatment with base, afforded, either in a separate step or in a one-pot procedure, the cyclized title compounds, i.e., the 4,5-dihydro-1,3-thiazoles 3 or the corresponding 5-6-dihydro-4H-thiazines 4via dehydrohalogenation.