BN-Embedded Aromatic Hydrocarbon Synthesis via Nucleophilic Diboration Reactions

A Mild and General trans-Diboration of Both Terminal and Internal Propargyl Alcohols

A practical and efficient trans-diboration of propargyl alcohols was accomplished using sodium hydride (NaH) as a base in N,N-dimethylformamide at room temperature. The mild reaction conditions demonstrate general applicability, facilitating the successful conversion of both terminal and internal propargyl alcohols with diverse structures and functional groups into highly functionalized alkenediboronates [4-borylated 1,2-oxaborol-2(5H)-oles]. The resulting products, which incorporate two boron groups, can be selectively activated and subjected to stepwise transformations, thereby providing an effective platform for synthesizing a wide range of structurally diverse trisubstituted alkenes.

N-Directed Two-Fold Bromoboration of Diynes Enables Access to Brominated BN-Embedded PAHs

N-directed 2-fold bromoboration reactions of diynes with BBr3 have been developed, allowing the access to novel internally BN-doped polycyclic aromatic hydrocarbons from readily available precursors under mild conditions. Computational investigations identified three potential reaction mechanisms, each involving either BBr3 or [BBr4]-, with low activation barriers (ΔG‡ < 16 kcal/mol) for all pathways. The resulting brominated products can be further functionalized through various cross-coupling protocols, enabling the synthesis of highly luminescent emitters with quantum yield exceeding 90.

Visible-Light-Induced trans-Hydroboration of Diaryl Alkynes Utilizing Excited State of Borate Complexes

We have developed visible-light-induced trans-hydroboration of diaryl alkynes via direct photoexcitation of in-situ-generated diboron complexes, affording previously elusive (E)-1,2-diaryl-vinylboronates with high stereoselectivity. Experimental, spectroscopic, and theoretical mechanistic studies revealed that the triplet-state borate complex facilitates B-B bond cleavage and the desired C-B bond formation. This methodology does not require any catalyst and is operationally simple. The highly borylated 1,2-diaryl alkenes [1-(2-borylphenyl)vinyl)boronates] are shown to be useful as building blocks.