Silver-Catalyzed Olefination of Aryl Aldehydes Using Propiolates

Olefination of aldehydes is one of the fundamental reactions in organic synthesis. The commonly used Wittig olefination reaction however uses stoichiometric quantities reagents under basic conditions resulting in stoichiometric amounts of byproducts. Known catalytic alternate to the Wittig reaction requires stoichiometric amounts of silane reducing agents and high temperature. Herein, we report a base-free olefination of aryl aldehydes using propiolates as a surrogate for the Witting reagent under silver catalysis. Trimethyl orthoformate, in the presence of a silver catalyst adds to the alkynoate to form the nucleophilic silver allenolate which reacts with the reactive oxocarbenium ion formed from aldehyde under the reaction conditions. Subsequently, decarbonylation occurs to form the olefin. Trans olefin is formed exclusively from simple aryl aldehydes and cinnamaldehydes. Such a silver allenolate is conceptually novel and has not been explored so far.