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
Graphical Abstract
Scheme 1: Mechanistic overview of enzymes involved in ring-size-altering reactions: A: Difference in ionisati...
Scheme 2: A: Ring contraction through involvement of carbocationic intermediates in thujane monoterpene biosy...
Scheme 3: Examples of concerted ring expansions of carbocation intermediates in PxaTPS8-catalysed cyclisation...
Scheme 4: Sequential ring expansions during astellifadiene (17) synthesis reported by Abe and co-workers.
Scheme 5: Cyclobutane ring expansion and sequential ring contractions catalysed by the synthase AITS in the b...
Scheme 6: Ring expansion and transannular ring contraction of a cyclopentane to cyclobutane in the biosynthes...
Scheme 7: Computationally elucidated concerted cyclisations/alkyl/hydride shifts during the biosynthesis of t...
Scheme 8: Cyclisation events and 6→5-ring contraction during the construction of epi-isozizaene (26) catalyse...
Scheme 9: Transannular cyclisations and 4→5-membered ring expansion through dyotropic 1,2-rearrangement of al...
Scheme 10: Ring expansion in presilphiperfolan-8b-ol (31) biosynthesis and ring contraction of the presilphipe...
Scheme 11: Ring contraction via transannular cyclopropanation and opening of cyclopropane in the biosynthesis ...
Scheme 12: The crucial CYP450-catalysed oxidative rearrangement defining the skeleton in gibberellin biosynthe...
Scheme 13: CYP450-mediated oxidation of cyclopentane methylene expanding the 8-membered ring in the biosynthes...
Scheme 14: CYP450-mediated oxidation of an exocyclic methyl group to effect transannular cyclisation across th...
Scheme 15: Non-enzymatic transannular aldol reaction enables the formation of the 5/13/3-tricyclic ring system...
Scheme 16: A: Oxidative ring expansion of a cyclopentane by incorporation of a methyl group in the biosynthesi...
Scheme 17: Rearrangement and ring expansion in the construction of the complex bridged carbon framework of and...
Scheme 18: Ketoglutarate-mediated oxidations of preaustinoid A1 (53) en route to complex meroterpenoids, B-rin...
Scheme 19: Proposed putative biosynthetic formation of the tigliane skeleton from an E,E,Z-triene.
Scheme 20: Photocatalytic tandem ring expansion/contraction of santonin to give photosantonin products and gua...
Scheme 21: A: Proposed biosynthesis of stelleroid B (66) from stelleranoid I (65) by ketol rearrangement; B: o...
Scheme 22: Singular examples of A,B-ring contractions and expansions in the biosynthesis of sesquiterpenoids e...
Scheme 23: A: plausible proposed biosynthetic pathway for the tigliane/ingenane skeletal rearrangement and 1,2...
Scheme 24: A: Multiple ring-size alterations during xenovulene A (90) biosynthesis; B: Ring contraction and re...
Scheme 25: Proposed biosyntheses of the complex, polycyclic terpenoid illisimonin A (97) and the bridged antro...
Scheme 26: Proposed biogenetic origin for the meroterpenoid liphagal (104) via epoxide-mediated ring expansion....
Scheme 27: Proposed biogenetic origin for the ring-contracted members of the taiwaniaquinol family.
Scheme 28: A: Schenck ene/Hock/Aldol cascade effecting B-ring contraction in atheronal B (113); B: Selective C...
Scheme 29: A: D-ring expansion of buxenone (118) via cyclopropanation towards buxaustroine A (119); B: Propose...
Scheme 30: Biosynthetic origin of alstoscholarinoids A (124) and B (125) via cascade oxidative rearrangement c...
Scheme 31: Biogenetic origin of the hedgehog signalling inhibitor cyclopamine (129) by tandem ring contraction...
Scheme 32: Proposed biogenetic origin of the B-ring contracted spirocyclic triterpenoid spirochensilide A (131...
Scheme 33: A: Proposed B-ring contraction during the biosynthesis of holophyllane A (133); B: B-ring contracti...
Scheme 34: Radical and ionic/polar mechanisms for the C-ring-contracted triterpenoids phomopsterone B (139) an...
Scheme 35: A: Plausible mechanism for the formation of schiglautone A (144) from anwuweizic acid (145); B: Pro...
Scheme 36: Reported biosynthetic proposal for the formation of B-ring expanded triterpenoids rhodoterpenoids A...
Scheme 37: A: Final reaction step in the synthesis of euphorikanin A (154), benzilic acid-type ring contractio...
Scheme 38: Tricyclic ring expansion in the Gui synthesis of gibbosterol A (158) and sarocladione (160) via Ru-...
Scheme 39: A: A-ring expansion during the Gui synthesis of rubriflordilactone B (161); B: Mechanism for the bi...
Scheme 40: Photosantonin rearrangement effects A/B ring contraction/expansion in Li’s synthesis of the complex...
Scheme 41: Tandem A/B ring expansion/contraction of an ergosterol derivative via pinacol rearrangement in the ...
Scheme 42: Synthetic studies towards cyclocitrinol (179) by A) the semisynthetic approach by Gui et al. using ...
Scheme 43: A: Bioinspired synthesis of spirochensilide A (131) by the Heretsch group via selective 8,9-epoxida...
Scheme 44: Baran’s synthesis of cortistatin A (191), expanding the B-ring through a cyclopropane fragmentation....
Scheme 45: Ding’s total synthesis of retigeranic acid (198) showcasing sequential 6→5 ring contractions.
Scheme 46: A: Oxa-di-π-methane (ODPM) rearrangement of a bicyclic ketone en route to silphiperfolenone (203); ...
Scheme 47: Biomimetic synthesis of liphagal (104) from sclareolide (221) by George and co-workers.
Scheme 48: Wu’s bioinspired synthesis of cucurbalsaminones B (224) and C (225) by photocatalytic oxa-di-π-meth...
Scheme 49: Baran’s total synthesis of maoecrystal V (230) featuring a pinacol rearrangement for ring expansion...
Scheme 50: A: Ketol rearrangement leading to ring contraction in the total synthesis of preaustinoid B; B: Ben...
Scheme 51: A: Scheidt’s synthesis of isovelleral (251) by pinacol rearrangement triggered by Mitsunobu conditi...
Scheme 52: Biomimetic transformations of simplified test substrates related to Euphorbia diterpenoids.
Scheme 53: A: First generation synthesis of taiwaniaquinones by benzilic acid-type rearrangement of the B-ring...
Scheme 54: A: Norrish type 1 radical recombination leading to ring contraction en route to cuparenone (272): 1...
Scheme 55: Ring contraction of a bridged D-ring system in the total synthesis of andrastatin D (280), terrenoi...
Scheme 56: Biomimetic synthesis of hyperjapone A (284) and hyperjaponol C (285) by George et al.
Scheme 57: Heretsch’ synthesis of dankastarones A (288) and B (289), swinhoeisterol A (290), and periconiaston...
Scheme 58: A: Zhang’s ring contraction during the synthesis of stemar-13-ene (295) by pinacol rearrangement; B...
Scheme 59: Trauner’s biomimetic synthesis of preuisolactone A (307) featuring a ring contraction via benzilic ...
Scheme 60: Bioinspired approaches for ring contraction/expansion reactions in the synthesis of alstoscholarino...
Scheme 61: A: Sarpong and Li, Wang and co-workers’ ring expansion of cephanolide A (313) to reach harringtonol...
