Diamond's elementary chiral constituent – skew-tetramantane – features extreme rigidity, stability and a precisely defined geometry, epitomizing the parent structure of a σ-helicene. While skew-tetramantane is naturally occurring in trace fractions in fossil fuels, efforts over several decades for its selective synthesis remained unfruitful. With the recent advances in photo- and transition metal catalysis to tame radical and carbene species, we now devised a targeted total synthesis of skew-tetramantane by means of a stereoselective adamantalogous cage-extension. A first cap attachment was thereby effected by a photocatalytic Giese reaction, while remarkable regio-, diastereo- and enantiocontrol were achieved by an intramolecular C(sp³)−H insertion using Davies' chiral rhodium catalysts. Density functional theory (DFT) calculations elucidate the origin of this high selectivity, revealing a stereoelectronically biased transition state governed by catalyst–substrate interactions. The fusion to the adamantine skew-tetramantane structure was completed after a Buchner–Curtius–Schlotterbeck ring expansion and a stereoselective Mukaiyama hydration by an intramolecular C(sp³)−H insertion of a nonstabilized carbenoid. Overall, this approach provides access to synthetic skew-tetramantane in isomerically pure form with σ-helicity defined by catalyst-control, marking a selective pathway to higher diamondoids.

[1] X.-Y. Li, C. Sparr. Stereoselective Total Synthesis of skew-Tetramantane. Nat. Chem. 2026, 18, 597. ChemRxiv 2025, 10.26434/chemrxiv-2025-bp807.

[2] X.-Y. Li, C. Sparr. Streamlined synthesis of triamantane from readily available starting materials. Helv. Chim. Acta 2026, 109, e70057.

[3] X.-Y. Li, C. Sparr. Stereoselective total synthesis of skew-tetramantane, diamond's chiral core. Eur. Pat. Appl. EP 25185320.6, filed June 2025.