Other Methods for Carbocyclic Construction: Agelastatin A (Afonso/Siopa), Sculponin U (Fu/Liu), Artatrovirenol A (Zhu), Methyl Phomopsenoate (Shi/Hou/Tu), Euphol (Micalizio)

Thorsten Bach of the Technical University of Munich showed that under irradiation, cycloheptencarboxaldehyde 1 was converted into the Z isomer. An active Diels-Alder dienophile, this combined at room temperature with isoprene 2, leading to the trans-fused bicycle 3 (J. Org. Chem. 2023, 88, 12844. DOI: 10.1021/acs.joc.3c01311).

Agelastatin A (6), isolated from the sponge Agelas dendromorpha, has shown potential as a lead compound for the preparation of antineoplastic agents. Carlos A. M. Alfonso and Filipa Siopa of the Universidade de Lisboa prepared the cyclopentane core 5 of 6 by irradiation of the pyridinium salt 4. The alcohol 5 so prepared was racemic, but the unwanted enantiomer was readily removed by enzymatic acetylation (Adv. Synth. Catal. 2023, 365, 2240. DOI: 10.1002/adsc.202300560).

The kaurane diterpenoid sculponin U (9) was isolated from the perennial herb Isodon sculponeatus. Shaomin Fu and Bo Liu of Sichuan University assembled the tricyclic core 8 of 9 by the photochemical cyclization of 7 (Angew. Chem. Int. Ed. 2023, 62, e202305516. DOI: 10.1002/anie.202305516).

Artatrovirenol A (12), isolated from Artemisia atrovirens, a perennial herbaceous plant mainly distributed in southern China and Thailand, showed cytotoxicity against human hepatoma cell lines. Jieping Zhu of the Ecole Polytechnique Fédéral de Lausanne envisioned that the cyclobutane 11 from the intramolecular photocyclization of the enol ether 10 could be elaborated to 12 (J. Am. Chem. Soc. 2023, 145, 24408. DOI: 10.1021/jacs.3c09683).

Methyl phomopsenoate (15) was isolated from the fungus Phomopsis amygdali, a causative agent of peach shoot blight in southern China. En route to 15, Lei Shi of the Harbin Institute of Technology, Si-Hua Hou of Shanghai Jiao Tong University and Yong-Qiang Tu of Lanzhou University achieved high diastereoselectivity in the carbonyl ene cyclization of the tricyclic 13 to the tetracyclic 14 (J. Am. Chem. Soc. 2023, 145, 21170. DOI: 10.1021/jacs.3c07044).

Euphol (18), the main toxin of the Damara milk bush Euphorbia damarana of the north-western desert areas of Namibia and southern Angola, is a representative tetracyclic triterpenoid. Glenn C. Micalizio of Dartmouth College installed the angular methyls of 18 by a series of planned 1,2 shifts, exemplified by the oxidative rearrangement of 16 to 17 (Org. Lett. 2023, 25, 5687. DOI: 10.1021/acs.orglett.3c02187).