First example of lewis acid catalyzed 3-substituted 5 -arylidene -1 -methyl -2-thiohydantoin formation

A survey of Lewis acids was conducted to facilitate the formation of arylidenethiohydantoins. The use of indium(III) triflate shows significant advantages in facilitating this reaction. In most examples, the Lewis acid promoted catalysis gave shorter reaction times, higher conversion, and better purity profiles as compared to the traditional uncatalyzed reactions.