Progresses on the Application of Stable Borane Adducts in the Synthesis of Organoborons

Abstract

Organoboron compounds are wildly used in organic synthesis, materials science, life and health science, etc. The development of synthetic methodologies of organoborons has therefore gained intense attention nowadays. Typically, Bis(pinacolato)diboron (B 2 Pin 2 ), pinacolborane (HBpin) and catecholatoborane (HBCat) are predominantly used as boron reagents in catalytic C-B bond forming reactions. Different from the above traditional boron reagents, borane adducts with strong Lewis bases, such as amines, phosphines, and N-heterocyclic carbenes, are promising boron reagents because of their readily accessibility, relatively high stability, and easy operation. Moreover, the different chemical properties of these stable borane adducts towards the traditional boron reagents provide possibilities for development of new C-B bond formation reactions. The applications of the stable borane adducts as terminal boron reagents in hydroboration of alkenes or alkynes, C-H bond borylation, carbene insertion into B-H bonds, cascade cyclization initiated by boryl radicals and substitutions, which provide new methods for the preparation of organoborons are reviewed in this paper.

Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

“…Since transition-metalcatalyzed insertion of carbenes into B-H bonds was first disclosed in 2013, it has become a good method for the construction of C-B bonds. [7][8][9][10] When diazo compounds, [11][12][13][14][15][16][17] alkynes, [18][19] or sulfoxonium ylides [20][21] are used as carbene precursors, this method enables the construction of many novel organoboranes in high yields with high regioselectivity and, in some cases, high enantioselectivity (Scheme 1a). Quite recently, insertion of unsaturated carbenes into B-H bonds has also been established as a method for constructing C(sp 2 )-B bonds.…”

Dirhodium‐Catalyzed Enantioselective B−H Bond Insertion of gem‐Diaryl Carbenes: Efficient Access to gem‐Diarylmethine Boranes

“…We reasoned that B À Hb ond insertion reactions of carbenes might be useful for the synthesis of gem-diarylmethine boranes.T ransition-metal-catalyzed asymmetric BÀ Hb ond insertion reactions of carbenes have provided an ew method for the synthesis of chiral organoboron compounds. [23][24][25][26][27][28][29][30][31][32][33] Since we reported the first example of ac opper-catalyzed asymmetric B À Hb ond insertion reaction with a-diazophenylacetate as ac arbene precursor, [25] catalytic asymmetric B À Hbond insertion reactions have been successfully used for enantioselective construction of BÀCb onds. Va rious carbene precursors such as a-diazophenylacetates, [25,27,33] a-diazophenylketones, [26,27] a-diazopropionates, [30,32] trifluorodiazoalkanes, [28] ene-yne-carbonyls, [29] and tosylhydrazones [31] have been used in these insertion reactions.A lthough with these progresses,t he catalytic enantioselective BÀHb ond insertion is still in its infancy compared with the closely related well-established catalytic enantioselective CÀHbond insertion.…”

Cu-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones to access benzylboronic esters

“…Organoboron compounds represent significant structural motifs in organic synthesis [1][2][3][4][5][6], developing novel and practical strategies for the synthesis of organoboron compounds is highly demanding in nowadays chemical society. Among various organoboron compounds, benzylboronic esters are unique alkylboron compounds.…”