An efficient route for the synthesis of 2-arylthiazino[5,6-b]indole derivatives

Substituted 2-thiobenzamidomethylindole derivatives (14a-e) were prepared by the reaction of 2-aminomethylindole (9) with substituted benzoyl chlorides, followed by sulfurization using Lawesson's reagent. Alternatively, these thioamides were obtained from the amine in one step in an efficient manner by using substituted benzaldehydes in the presence of sulfur, or at room temperature with the aid of substituted methyl dithiobenzoates. The Hugerschoff reactions of thiobenzamides (14a-e) with phenyltrimethylammonium tribromide provided the rare title 2-arylthiazino5,6-b]indoles (15a-e) in good yields. A convenient one-pot approach for the synthesis of 2-phenyl-1,3-thiazino5,6-b]indole (15a) from 2-aminomethylindole (9) is also described.