Thionation of ω-hydroxy amides with Lawesson's reagent: Synthesis of thioenamides and sulfur-containing heterocycles

The thionation of ω-hydroxy amides with Lawesson's reagent [LR: 2,4-bis(p-methoxyphenyl)-1,3,2,4-dithiaphosphetane-2,4-disulfide] is described. The treatment of 3-hydroxy amides 1 with LR exclusively gave thioenamides 2 in fair yields. The treatment of 4-hydroxy amides 5 with LR yielded sulfur-containing heterocycles such as tetrahydrothiophene-2-imines 6 and tetrahydrothiophene-2-thione 7a through cyclization of intermediates, 4-mercapto amides 8. The 5-hydroxy amides 13 also reacted with LR to afford tetrahydrothiopyrane-2-thione 14 as the the sole product.