Diels-Alder Cycloaddition: Sterpuren-4-one (Singh), Kidamycinone (Collet), Magellanine (Barriault), Cycloclavine (Wipf), Andranginine (Takayama), Illudinine (Dudley)

The sesquiterpenoid sterpuranes were isolated from the fungus Chondrostereum purpureum (Stereum purpureum), that causes silver leaf in plants. Vishwakarma Singh of the Indian Institute of Technology Bombay observed (J. Org. Chem. 2017, 82, 6268. DOI: 10.1021/acs.joc.7b00867) high diastereoselectivty in the Diels-Alder addition of ethyl acrylate 2 to 1 to give 3, enabling the construction of sterpuren-4-one (4).

The pluramycin family of antibiotics show significant anti-cancer activity. Sylvain Collet of the Université de Nantes developed (J. Org. Chem. 2017, 82, 5710. DOI: 10.1021/acs.joc.7b00544) a route to kidamycinone (8) by combining juglone (5) with the diene 6, followed by selective oxidation of the unstable initial adduct to give 7.

The tetracyclic alkaloid magellanine 11 was isolated from the club moss Lycopodium magellanicum. Louis Barriault of the University of Ottawa assembled (Angew. Chem. Int. Ed. 2017, 56, 6280. DOI: 10.1002/anie.201611606) the piperidine ring of 11 by the easily-scaled intramolecular Diels-Alder cyclization of 9 to 10.

The pentacyclic indole alkaloid cycloclavine 14 was isolated from the seeds of the African morning glory shrub Ipomoea hildebrantii. En route to 14, Peter Wipf of the University of Pittsburgh prepared (Angew. Chem. Int. Ed. 2017, 56, 324. DOI: 10.1002/anie.201608820) the amide 12 by an enantioselective cyclopropanation of allene, and cyclized it to 13.

Andraginine (17) was isolated from the flowering Chinese tree Kopsia arborea. Hiromitsu Takayama of Chiba University achieved (Org. Lett. 2017, 19, 2722. DOI: 10.1021/acs.orglett.7b01076) substantial diastereoselectivity in the cyclization of 15, prepared in enantiomerically pure form, to 16.

Illudinine (20) is a metabolite of the jack-o-lantern mushroom Clitocybe illudens. Gregory B. Dudley, now at West Virginia University devised (Org. Lett. 2017, 19, 858. DOI: 10.1021/acs.orglett.6b03887) a straightforward route to 20 based on the cyclization of 18 to 19.