Multigram Copper‐Catalyzed Borylation of Functionalized Terminal Alkynes with B2Pin2

Application of cheap and accessible reactants for copper-mediated borylation of functionalized terminal alkynes is described. Based on the thorough assessment of different ligands/additives for various types of substrates, a simple decision tree for the optimal reaction condition choice is proposed. Using the developed methodology, a series of synthetically valuable alkenyl boronates is prepared on 10–300 g scale in single run.

A comprehensive study of the commercially available ligands/additives in the formal copper-catalyzed hydroboration reaction of functionalized terminal alkynes is described. Based on the common reaction system (CuCl–B₂Pin₂), a set of common and inexpensive ligands or additives—namely, rac-BINAP, PPh₃, [(t-Bu)₃PH]BF₄, and LiCl—is tested for its effects on the borylation regioselectivity and overall reaction efficiency. The results observed demonstrate correlation between the substrate nature (propargylic, homopropargylic, or higher homolog) and the ligand, which can be used for the preferential preparation of linear or branched isomer of the target alkenyl boronic species. It is found that LiCl and (t-Bu)₃P can be used for preparation of β-substituted alkenyl boronates, whereas α-substituted isomers are preferentially obtained in the presence of triarylphopsphine ligands. The scope of the transformations covers derivatives of protected (homo)propargylic alcohols and amines and tolerated free alcohol, ether, silyl ether, ketal, ester, and alkene moieties. The practical utility of the discussed methodologies is proven by the multigram preparation of target building blocks (10…100 g for over 20 boronates, up to 300 g—for a few selected representatives).

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