Anionic four electron donor-based palladacycle-catalyzed 1,4-additions of arylboronic acids with α,β-unsaturated ketones and 1,2-additions of arylboronic acids with aldehydes and α-ketoesters are described. Our study demonstrated that palladacycles were highly efficient, practical catalysts for these addition reactions. The work described here not only opened a new paradigm for the application of palladacycles, but may also pave the road for other metalacycles as practically useful catalysts for such addition reactions including asymmetric ones.Anionic four electron donor-based palladacycles, one of the two general types of palladacycles (Figure 1), are readily accessible and air/moisture stable. 1,2 They have been demonstrated as efficient catalyst systems for a number of bond forming reactions including cross-coupling reactions. 1,3 Mechanistic studies suggested that in cross-coupling reactions such as the Suzuki couplings, palladacycles served as the sources of catalytically active species by undergoing transmetalation with organometallic reagents to form transmetalated intermediates such as A followed by reductive elimination (Scheme 1). As it has been established that the Pd(II) center in palladacycles could act as a Lewis acid, 1 we reasoned that when carbonyl moieties were present in the reaction system, in addition to undergoing reductive elimination to form Pd(0) species (Path A), A might coordinate with a carbonyl moiety to form complexes B (Path B) (Scheme 1). On the basis that elevated temperature, typically higher than 100 °C, was required for palladacycles to generate catalytically active species for cross-coupling reactions, 1 we surmised that the reductive elimination of A should be slow, especially at lower temperature. We further envisioned that at lower reaction temperature, such as room temperature, B might undergo aryl transfer to form addition products much faster than reductive elimination to form cross-coupling products (Scheme 1), and Type I palladacycles could thus catalyze addition reactions of arylboronic acids to carbonyl group-containing compounds, 4, 5, 6 a field that is currently dominated by Rh(I) catalysis chemistry. 7,8,9, 10,11,12 The exploration of such palladacycle-catalyzed addition reactions would create a new paradigm for palladacycle catalysis chemistry and may provide powerful catalyst systems for organic synthesis. In this communication, we established that Type I palladacycles could indeed act as efficient catalysts