Palladium-mediated CO 2 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.