Palladium-mediated CO2 extrusion followed by insertion of ketenes: translating mechanistic studies to develop a one-pot method for the synthesis of ketones

Abstract

Multistage mass spectrometry (MSn) experiments were used to explore extrusion–insertion (ExIn) reactions of the palladium complex [(phen)Pd(O2CPh)]+ (phen, 1,10-phenanthroline). Under collision-induced dissociation (CID) conditions, the organopalladium cation [(phen)Pd(Ph)]+ was formed via decarboxylation and was found to react with phenylmethylketene to yield the enolate [(phen)Pd(CPhMeC(O)Ph)]+ via an insertion reaction. A further stage of CID revealed that the enolate fragments via loss of styrene to form the acyl complex [(phen)Pd(C(O)Ph)]+. Formation of both the coordinated enolate and acyl anions is supported by density functional theory (DFT) calculations. Attempts to develop a palladium-mediated one-pot synthesis of ketones from 2,6-dimethoxybenzoic acid as the key substrate and the ketene substrates R1R2C═C═O (R1 = Ph, R2 = Me; R1 = R2 = Ph) proved challenging owing to low yields and side product formation.