Friedel–Crafts acylation via interrupted Beckmann fragmentation of activated ketones

Abstract

Friedel–Crafts (FC) acylation has long been a fundamental electrophilic arene substitution reaction. In this work, we report a new procedure for FC acylation utilizing stable and user-friendly acylium precursors, α-oximinoketones. The key to this methodology is the selective C_sp²–C_sp² bond cleavage in α-oximinoketones, facilitated by triflic anhydride, leading to the formation of acylium ions under mild conditions. This approach demonstrates compatibility with a variety of substituted alkyl, (hetero)aryl ketones, and cyclic ketones as acylating reagents, where cyclic ketones allow for unique ring-opening FC acylation without relying on ring strain. DFT calculations confirmed the mechanistic pathway, highlighting the generation of acylium ions via the selective Beckmann fragmentation over Beckmann rearrangement.