The following part of the text needs to replaced: Mechanistic studies by Friestad and Branchaud[16] on the Cacchi system suggested that the absence of acid would result in the initial formation of the Mizoroki–Heck product 4a, followed by its reduction to 3a by accumulated Pd-H species formed from NBu3. To study this hypothesis in our present catalyst system, we carried out a reaction with deuterated benzylidene acetone ([D1]-1 a) under the optimized reaction conditions (Scheme 2). Either the absence of deuterium or deuterium scrambling at the b-carbon of 3a, will support the reaction pathway via Heck reaction followed by reduction. However, the reaction gave reductive Heck product [D1]-3 a in 80% yield with=97% remaining deuteration at the b-carbon. This rejects the hypothesis of Friestad and Branchaud and supports the pathway in which the Pd-alkyl complex A (Scheme 1) is reduced by DIPEA to a palladium hydride species followed by reductive elimination. Alternatively A tautomerizes to an O-bound palladium enolate that is subsequently reduced by DIPEA.[20] This part should be replaced by the following: We have performed a deuterium labelling experiment to shed more light on the mechanism of the reaction (Scheme 2). Thus, reaction of 4-d-phenyl-3-buten-2-one ([D1]-1 a) with 2a and 5 eq. of DIPEA catalyzed by 1 mol% of Pd(OAc)2 gave the reductive arylation product [D1]-3a in 80% yield with 97% retention of deuterium. This conclusively shows a reductive arylation mechanism is active and it excludes the possibility of a Heck reaction followed by a hydrogenation, as in this case all deuterium would be lost. However, the final stages of the mechanism remain obscure. We see two possible mechanisms: protonation of the formed palladium enolate species and reduction of the palladium(II) to palladium(0) with the trialkylamine. The second mechanism: reaction of the palladium alkyl intermediate with the trialkylamine to form the palladium alkylhydride complex seems quite plausible. Reductive elimination of this will lead to the reductive arylation product. A third mechanistic possibility, previously proposed by Friestad and Branchaud, suggested reduction of the palladium enolate by XPdII(Ln)H, EtNHX, or other reductants.[16] However, we have shown in later work that upon use of [D15]Et1N 55% of deuterium is incorporated a to the ketone in the 3-position, providing strong support for the second mechanism.[20].