Unsymmetrical 1,1-Bisboryl Species: Valuable Building Blocks in Synthesis

Abstract

Unsymmetrical 1,1-bis(boryl)alkanes and alkenes are organo-bismetallic equivalents, which are synthetically important because they allow for sequential selective transformations of C–B bonds. We reviewed the synthesis and chemical reactivity of 1,1-bis(boryl)alkanes and alkenes to provide information for the synthetic community. In the first part of this review, we disclose the synthesis and chemical reactivity of unsymmetrical 1,1-bisborylalkanes. In the second part, we describe the synthesis and chemical reactivity of unsymmetrical 1,1-bis(boryl)alkenes.

Stereoselective Diels-Alder Reactions of gem-Diborylalkenes: Toward the Synthesis of gem-Diboron-Based Polymers via ROMP

“…21,29,33 This is in a good agreement with the fact that the aromaticplanar Bdan group is less bulky than the Bpin group. 13,27,32,42 Therefore, it would appear that the diastereoselectivity in this case is driven primarily by sterics.…”

“…It was anticipated that the cycloaddition might proceed with good stereoselectivity (Figure 4). 13 We were happy to discover that the reaction of 1,1 BpinBdan-ethene (2') with dienes 3a-d afforded the unsymmetrical gem-diborylalkane 5a-d (confirmed by X-ray crystallographic analyses of 5a and 5c) in good yield (Figures 4A-B). High diastereoselectivity was observed in the reaction of 2' with CP, affording cycloaddition product 5c (endo:exo = 92:8).…”

“…28,30 Recently, we reported a photoredox-mediated reaction of gemdiborylalkenes 31 and showed that gemdiboryalkenes (2) are more electron deficient compared to vinyl-boron 1; 31 hence, 2 should serve as a suitable dienophile for this type of cycloaddition reaction. However, key challenges include: (1) the steric repulsion introduced by the two groups of the bulky Bpin units in the TS of the cycloaddition reaction 32 (2) whether the regio-and stereoselectivity of the cycloaddition can be controlled when two unsymmetrical boron groups are placed on the geminated carbon of dienophile 2' 13 (3) whether the reaction can proceed in a regioselective manner when borylated dienes react with 2 (Figure 2B)? 28 To answer these questions, we first conducted computational studies on the DA reaction to predict whether gem-diborylalkenes (2) could be used as dienophile reactive partners for the DA reaction.…”

“…These two different boron groups can provide the basis for selective C-B sequential functionalization, which in turn, reacts differently. 13,43 Unlike boronic-esters, for example, the Bpin and Bdan groups, mono-alkyl-trifluoroborate salts are known to be easily activated and to undergo rapid transmetalation with transition-metal complexes. In general, owing to their air, moisture, shelf, and thermal stability, as well as their occurrence as freeflowing crystalline solids, monotrifluoroborate salts have now become extremely popular reagents in synthesis.…”

“…8 Therefore, over the last decade, much effort has been expended to synthesize new functionalized classes of polyboronates, which have been shown to be excellent building blocks for the modular construction of new compounds. [9][10][11][12] Among polyboron-containing structural motifs, (unsymmetrical) 13 gem-diboron derivatives (2, 3') are a well-known emerging class with good potential for novel synthetic applications (Figure 1A). [14][15][16][17] The special properties and structures of bisnucleophile gem-diboryl compounds 2, 3' (termed geminated organodimetallics) 18,19 have attracted increasing attention from synthetic chemists, particularly in constructing C-C/ C-heteroatom bonds.…”