Copper-Catalyzed Regioselective Formation of Tri- and Tetrasubstituted Vinylboronates in Air

Abstract

The first "in air" copper-catalyzed method for the selective synthesis of tri-and tetrasubstituted vinylboronate derivatives is presented. Three different variants of the borylation of internal alkynes (α-hydroboration, β-hydroboration, and carboboration) are described using a single catalyst: [Cu(Cl)(IMes)] (IMes = N,N′-bis-[2,4,6-(trimethyl)phenyl]imidazol-2-ylidene) without taking any precaution to avoid the presence of air. Bis(pinacolato)diboron was used to afford β-hydroborated products in the presence of methanol. Adding instead another electrophile allowed the formation of tetrasubstituted vinylboronate species. Finally, the α-products were obtained using pinacolborane as the boron source. All compounds were obtained in high yield with excellent regioselectivity at low catalyst loading (0.04−2 mol %). The protocol constitutes a very convenient route to access these highly valuable molecules.

Synthesis, Structural Characterization and Catalytic Activities of Sulfur‐Functionalized NHC–Copper(I) Complexes

“…In a survey of the catalytic activity of the obtained copper complexes bearing a thioether chain, we also employed a hydroboration reaction of triple and double bonds. Based on the efficient methodology presented by Cazin's group, we applied their general conditions in our experiments (Table ) …”

“…For the evaluation step, we used 1‐phenyl‐1‐butyne as the benchmark substrate. At 0.05 mol‐% catalyst loading, we compared the three NHC–copper catalysts containing a sulfur moiety ( 5Cl , 8Cl and 12Cl ) with activity data reported for well‐known copper systems (IPrCuCl and IMesCuCl) (Table ) . In most cases, product P15 was formed in very good yields (93–98 %) and with high regioselectivity.…”

Copper–NHC complexes in catalysis

“…[Cu(Cl)(IMes)] catalyzed the α-and -hydroboration as well as the carboboration. Indeed, using B 2 pin 2 as the boron source, the selectivity was enhanced towards the -substituted derivative, while HBpin gave the α-product [71].…”

Cyclodextrin Cavity‐Induced Mechanistic Switch in Copper‐Catalyzed Hydroboration

“…[17] Remarkably, inversions of regioselectivities have been observed, particularly by introducing different copper ligands. [18][19][20][21][22][23] For aryl-substituted terminal alkynes, and with nonbulky ligands, the selectivity is generally in favor of the linear adduct (or -product, Scheme 1).…”