Enantioselective palladium-catalyzed carbonylation of gem-dibromoalkenes to chiral benzo[7]annulenes.

A palladium-catalyzed asymmetric monocarbonylation of benzo[7]annulene-based gem-dibromoalkenes yields inherently chiral tetrasubstituted benzo[7]annulene derivatives with up to 97% yield and up to 98:2 er.

• Why it matters: Achieving chemo- and enantioselective mono-debrominative carbonylation of gem-dibromoalkenes is difficult due to competing double functionalization and poor enantiocontrol from a prochiral alkene plane.
• What they did: The authors used a palladium-catalyzed asymmetric monocarbonylation of conformationally rigid, prochiral benzo[7]annulene gem-dibromoalkenes, and showed that simple acid additives switch to double debrominative carbonylation.
• The result: Acid-enabled pathway switching delivers inherently chiral trisubstituted vinyl carboxylic acids with similarly good chemo- and enantiocontrol, and DFT-supported mechanistic work implicates an acid-induced alkylidene carbene–Pd–H species for the divergence.

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