Efficient synthesis of 2-and 3-substituted indenes from 2-bromobenzyl bromide through an enolate alkylation/Cr(II)/Ni(II)-mediated carbonyl addition sequence

An efficient new synthesis of 2- and 3-substituted indenes has been developed based on the nickel-catalyzed chromium(II)-promoted addition of aryl bromides to a tethered ketone carbonyl. Several tethered bromoaryl ketones were prepared through enolate alkylation of acyclic or cyclic ketones with 2-bromobenzyl bromide. Nozaki-Takai-Hiyama-Kishi closure of the resulting bromoaryl ketones followed by acid promoted dehydration gave substituted indenes in overall yields for the three-step sequence ranging from 29 to 58%. (C) 1999 Elsevier Science Ltd. All rights reserved.