Thionation of N-(omega-halogenoalkyl)-substituted Amides with Lawesson's reagent: Facile synthesis of 4,5-dihydro-t3-thiazoles and 5,6-dihydro-4H-1,3-thiazines

The thionation and cyclization of N-(omega-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 4 via dehydrohalogenation.