Divergence from the classical hydroboration reactivity; boron containing materials through a hydroboration cascade of small cyclic dienes

Enantioselective Total Synthesis of (-)-Vinigrol: The Evolution of a Transannular Diels-Alder Strategy

Vinigrol is a structurally and stereochemically complex diterpenoid that displays various potent pharmacological activities. Two generations of synthetic routes were designed and pursued based on a transannular Diels-Alder (TADA) cycloaddition strategy. An intramolecular [2 + 2]photocycloaddition in the presence of the chelating Lewis acid (MgBr2·Et2O) was first discovered to enable the reaction of sterically challenging substrates, which was followed by [2 + 2]cycloreversion to provide α-pyrones fused with a 10-membered ring. Eventually, a new and scalable synthetic route toward (-)-vinigrol was developed and provided over 600 mg materials, manifesting the power of macrocyclic stereocontrol and TADA reaction.

B-B Bond Nucleophilicity in a Tetraaryl μ-Hydridodiborane(4) Anion

The tetraaryl μ‐hydridodiborane(4) anion [2H]⁻ possesses nucleophilic B−B and B−H bonds. Treatment of K[2H] with the electrophilic 9‐H‐9‐borafluorene (HBFlu) furnishes the B₃ cluster K[3], with a triangular boron core linked through two BHB two‐electron, three‐center bonds and one electron‐precise B−B bond, reminiscent of the prominent [B₃H₈]⁻ anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M⁺=Li⁺, K⁺) with MeI or Me₃SiCl leads to equimolar amounts of 9‐R‐9‐borafluorene and HBFlu (R=Me or Me₃Si). Thus, [2H]⁻ behaves as a masked [:BFlu]⁻ nucleophile. The HBFlu by‐product was used in situ to establish a tandem substitution‐hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3‐propylene‐linked ditopic 9‐borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R₂BFlu].

Nanoscale boron carbonitride semiconductors for photoredox catalysis

The conversion of solar energy to chemical energy achieved by photocatalysts comprising homogeneous transition-metal based systems, organic dyes, or semiconductors has received significant attention in recent years. Among these photocatalysts, boron carbon nitride (BCN) materials, as an emerging class of metal-free heterogeneous semiconductors, have extended the scope of photocatalysts due to their good performance and Earth abundance. The combination of boron (B), carbon (C), and nitrogen (N) constitutes a ternary system with large surface area and abundant activity sites, which together contribute to the good performance for reduction reactions, oxidation reactions and orchestrated both reduction and oxidation reactions. This Minireview reports the methods for the synthesis of nanoscale hexagonal boron carbonitride (h-BCN) and describes the latest advances in the application of h-BCN materials as semiconductor photocatalysts for sustainable photosynthesis, such as water splitting, reduction of CO₂, acceptorless dehydrogenation, oxidation of sp³ C-H bonds, and sp² C-H functionalization. h-BCN materials may have potential for applications in other organic transformations and industrial manufacture in the future.