Norbornene Derivatives-Controlled Palladium-Catalyzed Divergent Synthesis of Dibenzo[a,c]cycloheptenones and Fluorenones from Aryl Iodides and -Oxocarboxylic Acids

A palladium-catalyzed divergent cascade decarboxylative annulation of aryl iodides and alpha-oxocarboxylic acids using norbornene (NBE) derivatives as a controlled switch is reported. When NBE is used as a mediator, fluorenones are synthesized with moderate to excellent yields via a Catellani reaction that involves sequential ortho-C-H arylation and ipso-decarboxylative acylation of aryl iodides. Employing oxanorbornadiene (ONBD) instead of NBE enables the assembly of dibenzo-[a,c]-cycloheptenones by a retro-Diels-Alder reaction rather than the release of an ONBD. Additionally, the synthetic utility of this method is demonstrated by the diversification of the products.