The synthesis of strained carbocyclic building blocks is relevant for Medicinal Chemistry, and methylenecyclobutanes are particularly challenging with current synthetic technology. Careful inspection of the reactivity of [1.1.1]propellane and diboron reagents has revealed that bis(catecholato)diboron (B2cat2) can produce a bis(borylated) methylenecyclobutane in a few minutes at room temperature. This reaction constitutes the first example of B-B bond activation by a special apolar hydrocarbon and also the first time that propellane is electrophilically activated by boron. Mechanistic studies including in situ NMR kinetics and DFT calculations demonstrate that the diboron moiety can be directly activated through coordination with the inverted sigma bond of propellane, and reveal that DMF is involved in the stabilization of diboronate ylide intermediates rather than the activation of the B-B bond. These results enable new possibilities for both diboron and propellane chemistry, and for further developments in the synthesis of methylenecyclobutanes based on propellane strain release.

A catalyst-free 1,2-diborylation of aryllithium with tetra(o-tolyl)diborane(4) has been achieved, giving a series of 1,2-diborylaryl lithium species in excellent yields under mild reaction conditions, which leads to 1,2-di(tolyl)borylarenes in 60-91 % yields upon treatment with the hydride-abstracting reagent. In these transformations, one sp2 C-H of arene is activated and both boryl units are utilized to build two new (sp2 )C-B bonds. This represents a new strategy for selective arene diborylation. Density functional theory (DFT) calculations suggest that an aromatic nucleophilic substitution is a key step in the formation of the products.

A method has been described for accessing α-seleno alkyl boronates. The selenoboration was achieved via the diboration of carbonyl compounds to give α-oxyl boronates, which then undergo 1,2-metalate rearrangement in the presence of lithium selenolates and trifluoroacetic anhydride (TFAA). A variety of structurally diverse substrates were compatible with this protocol and efficiently provides difunctionalized products from simple starting materials. The presence of the boronic ester in the resulting organoselenium compounds serves as a versatile synthetic handle for various functionalizations. Mechanistic studies revealed that the binding of selenium nucleophile to both the boron centers in α-oxyl boronate esters.

We report an asymmetric synthesis of enantioenriched gem-bis(boryl)alkanes in an enantioselective diborylation of 1,1-disubstituted alkenes catalyzed by Co(acac)2 /(R)-DM-segphos. A range of activated and unactivated alkenes underwent this asymmetric diborylation in the presence of cyclooctene as a hydrogen acceptor, affording the corresponding gem-bis(boryl)alkanes with high enantioselectivity. The synthetic utility of these chiral organoboronate compounds was demonstrated through several stereospecific derivatizations and the synthesis of sesquiterpene and sesquiterpenoid natural products.

We report the first catalytic diborylation of 1,1-disubstituted vinylarenes with pinacolborane using a cobalt catalyst generated from bench-stable Co(acac)2 and xantphos. A wide range of 1,1-disubstituted vinylarenes underwent this transformation to produce the corresponding gem-bis(boryl)alkanes in modest to high yields. This cobalt-catalyzed reaction can be readily conducted on a gram scale without the use of a dry box and represents a practical and effective approach to prepare a wide range of branched gem-bis(boryl)alkanes.

Multisubstituted olefins are fundamental motifs in organic compounds. In this account, we describe the synthesis of organic molecules bearing an olefinic moiety by the transition-metal-catalyzed regio- and stereoselective addition of a variety of interelement compounds to alkynes. Regio- and stereoselective silaboration, diborylation, and chlorothiolation have been achieved by using the transition-metal catalysts. The subsequent cross-coupling reactions of the boron-containing alkenes to install various aryl groups afforded the corresponding tri- and tetraarylated olefins. This account describes our research on the highly regio- and stereoselective synthesis of multifunctionalized olefins such as tetraarylethenes with four different aryl groups.