Cleavage of halogenobenzophenones by potassamide in ammonia; new routes to xanthen- and thioxanthen-9-ones
Abstract
Treatment with potassamide in ammonia cleaved 2-chloro-4′-methoxy- and -4′-methylthio-benzophenones to give 4-methoxy- and 4-methylthio-benzoic acids respectively, but 2-chloro-4′-hydroxybenzophenone was largely unchanged. Similar treatment of 2′-fluoro-2-hydroxy-5-methylbenzophenone gave mainly 2-methyl-xanthen-9-one; the 2′-chloro- and 2′-bromo-analogues gave the xanthenone and the corresponding 2′-aminobenzophenone. 3′-Fluoro-2-hydroxy-5-methylbenzophenone was largely unchanged under these conditions, but the 3′-chloro- and 3′-bromo-analogues gave 2-methylxanthen-9-one and the corresponding 3′-aminobenzophenone. 2-Methylthioxanthen-9-one was prepared by two routes: (i) from 2-chlorobenzoyl chloride, 4-methylthiotoluene, and aluminium chloride; and (ii) from 3′-chloro-5-methyl-2-methylthiobenzophenone and potassamide in ammonia.