Ring contraction and ring expansion reactions in terpenoid biosynthesis and their application to total synthesis

• Nicolas Kratena,
• Nicolas Heinzig and
• Peter Gärtner

Beilstein J. Org. Chem. 2026, 22, 289–343, doi:10.3762/bjoc.22.21

• ring-expansion strategies in relevant natural product syntheses will be presented, demonstrating how synthetic chemistry can help to elucidate plausible biogenetic routes for structurally complex natural products. Keywords: biosynthesis; rearrangement; ring contraction; ring expansion; skeletal

• editing; terpenoids; total synthesis; Introduction The vast richness of structural diversity in terpenoid natural products has fascinated organic chemists for more than a century now [1][2][3][4][5]. With more sophisticated techniques for isolation and characterisation emerging over the decades

Comparative analysis of complanadine A total syntheses

• Reem Al-Ahmad and
• Mingji Dai

Beilstein J. Org. Chem. 2025, 21, 2334–2344, doi:10.3762/bjoc.21.178

• strategies and creative tactics, reflecting how emerging synthetic capabilities and concepts can positively impact natural product total synthesis. Keywords: biomimetic synthesis; C–H functionalization; complanadine; lycopodium alkaloid; skeletal editing; total synthesis; transition metal catalysis

• a novel single-atom skeletal editing strategy [32][33] to form the pyridine from a pyrrole and a similar pyridine N-oxide directed ortho C–H arylation to forge the C2–C3’ linkage as the Tsukano synthesis, but with a much less reactive 3-chloropyridine as the cross-coupling partner. As shown in

• of the electron-rich pyrrole group is essential for the key C–C bond formation. In the next step, the pyrrole group was converted to the pyridine group encoded by the natural product. This single-atom skeletal editing step (67 → 68) was achieved using the Ciamician–Dennstedt rearrangement, a reaction

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• and aldehyde protecting groups. Recently, Lebold, Sarpong, and co-workers showed that 1,2-BCPs (±)-14a–e are also accessible from 1,5-disubstituted 2-azabicyclo[2.1.1]hexanes 13 (2-aza-1,5-BCHs) through a skeletal editing strategy utilising commercially available Levin’s reagent [30][31] (Scheme 1D