Radical Chemistry in Organoboron Synthesis

Radical methodologies have revolutionised the preparation and diversification of organoboron compounds by exploiting boron-centred and carbon-centred radical intermediates. These approaches harness mild activation modes such as visible‐light photoredox catalysis and heterogeneous photocatalysis to generate boryl radicals or transient carbon radicals that engage in selective bond‐forming events. Key advances include regioselective radical α‐borylation of electron‐poor alkenes, diastereoselective radical cascades and stereocontrolled hydrogen‐atom transfers, enabling the rapid assembly of complex scaffolds bearing C–B, C–C and C–X linkages. The operational simplicity, functional-group tolerance and potential for stereocontrol render radical organoboron protocols attractive for the synthesis of bioactive molecules, agrochemicals and materials precursors. Moreover, the integration of eco-friendly heterogenous catalysts and metal-free systems has enhanced scalability and industrial relevance, underscoring the global impact of this flourishing field.

Research from Nature Portfolio

Recent studies have demonstrated a heterogeneous photocatalytic route to diastereoselective hydroboration of indole derivatives using vacancy-rich polymeric carbon nitride and NHC–borane reagents. This protocol achieves trans-hydroboration with high selectivity and broad substrate scope, offering an eco-friendly and cost-effective alternative to homogeneous catalysts for the preparation of boron-functionalised heterocycles. Another report has introduced a stereodivergent radical cascade in which NHC-boryl radicals trigger addition–translocation–cyclisation sequences, followed by controlled hydrogen-atom transfer to acyclic carbon radicals. By tuning the NHC ligands, thiol cocatalysts or Lewis-acid chelation, complementary facial selectivity is achieved, enabling access to both diastereomers of boron-tethered heterocycles. A foundational contribution described a regioselective radical α-borylation of α,β-unsaturated carbonyl compounds, affording α-boryl carbonyl building blocks with exceptional functional-group compatibility. Mechanistic studies revealed that radical addition versus hydrogen‐atom transfer dictates α-regioselectivity, guiding the design of further radical borylation processes.

Radical Chemistry in Organoboron Synthesis publication trend

The graph below shows the total number of articles in radical chemistry in organoboron synthesis across all publications each year (not limited to Nature Index journals).

Technical terms

Boryl radical: A boron-centred radical species capable of adding to unsaturated substrates or abstracting atoms to form new bonds.

Hydrogen‐atom transfer (HAT): A radical mechanism in which a hydrogen atom is transferred between a radical and a non‐radical species, often controlling stereochemistry.

Halogen‐atom transfer (XAT): A process in which a radical abstracts a halogen atom from an organic halide, generating a new carbon‐centred radical.

Photocatalysis: Activation of substrates via light‐excited catalysts, enabling single‐electron transfer pathways under mild conditions.

Radical cascade: A sequence of radical reactions where one radical event triggers subsequent bond-forming steps, rapidly building complexity.

N‐heterocyclic carbene (NHC): A neutral, strong σ-donating ligand stabilising borane adducts and facilitating radical generation.

References

1. Diastereoselective dearomatization of indoles via photocatalytic hydroboration on hydramine-functionalized carbon nitride. Nature Communications (2024).
2. Photocatalytic Boryl Radicals Triggered Sequential B─N/C─N Bond Formation to Assemble Boron‐Handled Pyrazoles. Advanced Science (2023).
3. Formation of C–B, C–C, and C–X Bonds from Nonstabilized Aryl Radicals Generated from Diaryl Boryl Radicals. ACS Central Science (2023).
4. Regioselective radical α-borylation of α,β-unsaturated carbonyl compounds for direct synthesis of α-borylcarbonyl molecules. Nature Communications (2019).
5. Photoinduced Halogen-Atom Transfer by N‑Heterocyclic Carbene-Ligated Boryl Radicals for C(sp3)–C(sp3) Bond Formation. Journal of the American Chemical Society (2022).
6. Stereoselective hydrogen atom transfer to acyclic radicals: a switch enabling diastereodivergent borylative radical cascades. Nature Communications (2022).