Copper-Catalyzed Chemo-, Regio-, and Stereoselective Ring-Opening sp<sup>2</sup>/sp<sup>3</sup> Diborylation of Arylidenecyclopropanes
Shanglin Chen, Junmei Lin, Qiuling Song
Abstract
A copper-catalyzed sequential hydroboration/isomerization/boryldemetalation reaction of arylidenecyclopropanes (ACPs) is reported, furnishing a straightforward and efficient route for the assembly of valuable 1,3-diboronates featuring both sp 2 /sp 3 C–B bonds. In contrast to the established CuH-induced ring-opening cascade hydrofunctionalizations of ACPs, which afford diverse sp 3 /sp 3 1, n -diboronates, silylboronates, or aminoboronates, CuBpin species-catalyzed diborylation variant remains unexplored. Particularly, the envisioned ring-opening regioselective hydroboration followed by boryldemetalation of homoallylic copper intermediates to concurrently construct both sp 2 - and sp 3 -hybridized C–B bonds in a one-pot transformation represents a significant knowledge gap in this field. Herein, we present the Cu-catalyzed chemo-, regio-, and stereoselective ring-opening sp 2 /sp 3 diborylation of ACPs. Control experiments are conducted to illustrate the flexible transformation of Cu–H into Cu–Bpin and the essential significance of NaBEt 3 H in this transformation. The synthetic practicality of our presented protocol is further demonstrated by gram-scale preparation within a short period and the selective derivatization of the two types of boron moieties, enabling access to diversified high-valued 1, n -diboron compounds ( n = 3, 5, 6), β-hydroxy ketones, 1,3-diols, α,β-unsaturated ketones, thermodynamically unstable cis -homoallylic boronate, and cis -homoallylic alcohol.