We started our study with the reaction of model substrate 2a under the conditions reported previously for the reactions of ester 1 and 2-halopyridines. To our delight, heating compound 1, boronate 2a, and excess of copper powder in DMSO at 65 C gave desired product 4a in 33% yield with 100% conversion of starting boronate 2a (Table , Entry 1). Introducing equivalent amounts of 1,10-phenantroline (Entry 2) or TMEDA (Entry 3) diminished the product yield to 0% and 11%, respectively. On the contrary, the use of a catalytic amount of TMEDA resulted in a significant increase in the product yieldto 78% (Entry 3). Alternative reaction promotors were also tested (i.e., Fe, Zncatalytic CuSO4, and CuI), but they were less effective or ineffective at all (Entries 5-7). Interestingly, lowering the metallic copper loading down to 50% and thento 10% mol. had a minor impact on the product yield that could be alleviated by prolonged reaction time (Entries 8 and 9). Further decrease of the Cu amount (to 1% mol.) still allowed obtaining product 4a in 74% yield; however, an increased reaction time (48 h) and amount of 1 (additional 0.5 eq.) were required to achieve the full conversion. Other additives were also checked by performing the reaction in the presence of organic (Entries 11 and 12) and inorganic (Entries 13 and 14) bases. With organic bases, a significant drop in the product yield and the conversion rate was observed. On the contrary, the use of inorganic bases led to a full conversion of the starting material but significantly (for NaOAc) or slightly (for NaHCO3) lower yield of target product 4a. Other variations of the reaction conditions (including temperature, solvent, reactant concentrations, and additive amount) did not improve the reaction outcome (the details can be found in the Supporting Information). NaHCO3 (0.2 eq) 78/0 14 NaOAc (0.2 eq) 28/0 Yield of 4a and amount of unreacted 2a according to H NMR spectra after 8 h. After 18 h. After 48 h.