Catalytic Intramolecular Ketone Haloacylation Enabled Stereoselective Heterolytic Cleavage of Cyclopropyl Ketones with Enhanced Reactivity and Regioselectivity beyond Electronics

Abstract

By integration of oxocarbenium activation and Lewis acid coordination activation via conformational proximity-driven, Pd(II)-or Cu(I)-catalyzed intramolecular ketone haloacylation, regio-and stereoselective heterolytic ring-opening 1,5-haloacylation of cyclopropyl ketones, including those with weak single alkyl donors, has been developed for the synthesis of valuable αquaternary halo-γ-butenolides. The vicinal carboxylic acid and ketone acceptors are no longer just spectator activators. Further, this reaction delivers a constant regioselectivity regardless of the electronic nature of substituents, even the malonate.

Divergent Aromatization of α-Halobenzyl γ-Butenolides Initiated by Selective Enol Protonation to Benzo[c]fluorenones and Naphthalenes

“…We recently proposed a new cyclopropane activation strategy based on cooperation of the cis -aligned ester and ketone groups on a cyclopropane ring via the formation of cyclopropane-fused oxocarbenium intermediates . The strategy afforded a divergent approach for they synthesis of 3- and 5-ylidenebutenolides from cyclopropyl γ-ketoesters promoted by TfOH .…”