Stereoselective Unsymmetrical 1,1‐Diborylation of Alkynes with a Neutral sp²−sp³ Diboron Reagent

Abstract

The incorporation of two distinct boryl groups at the same carbon center in organic molecules has attracted growing research interest due to its potential for facilitating controlled, precise synthesis through stepwise dual carbon‐boron bond transformations. Here we report a method to access unsymmetrical 1,1‐diborylalkene (UDBA) stereoselectively via the reaction of readily available alkynes with a neutral sp2‐sp3 diboron reagent (NHC)BH2‐Bpin (NHC = N‐heterocyclic carbene). Attributing to the chemically easily distinguishable nature of the sp2 and sp3 boryl moieties, controllable stepwise derivatization of the resultant UDBAs is realized. This process leads to various multifunctionalized olefins and organoborons, such as acylboranes, which are difficult to prepare by other methods.

Desymmetrization of Diboron(4) by a Trifluorination B-Masking Strategy: Practical Synthesis of Unsymmetrical Diboron Species

“…Such investigations are expected to greatly enhance the existing approaches for derivatizing noble diboron motifs and enable the creation of new connections. While the initial instance of sp 2 –sp 3 hybridized diborane, i.e., monoetherate tetrachlorodiborane(4) (B 2 Cl 4 OR), was documented in 1949 by Schlesinger, the first conclusive confirmation of such a species occurred in 1972 by Timms and colleagues. , In their work, the product (SiCl 3 ) 2 B(CO)B(Cl) 2 was identified as a neutral sp 2 –sp 3 diborane, and the conformation of this species was corroborated by the observation of two signals–peaks in 11 B NMR. , Subsequently, in recent years, new methods for unsymmetrical diboron(4) synthesis have been developed that enable the creation of novel families of these species. − Selected examples ( 1 – 9 ) of these methods are outlined in Figure . − …”