Total Synthesis via Diels-Alder Cycloaddition: Brevianamide B (Scheerer), Nicolaiodesin C (Lei), Mesembrine (Snyder), α-Yohimbine (Tan), Periconiasin A (Liu/Tang), Eupesegetanin A (Qiu)
Diels-Alder cycloaddition is not limited to all-carbon systems. En route to brevianamide B (4), Jonathan R. Scheerer of the College of William & Mary prepared (J. Org. Chem. 2016, 81, 2293. DOI: 10.1021/acs.joc.5b02744) 3 by adding β-nitroacrylateb 2 to the azadiene 1.
To achieve enantioselective addition to myrcene (6), Xiaoguang Lei of Peking University added (J. Org. Chem. 2016, 81, 458. DOI: 10.1021/acs.joc.5b02248) a stoichiometric amount of a 1:1 complex of Vanol and BH3 to 5. The adduct was deacetylated to give nicolaiodesin C (7).
In the course of a synthesis of mesembrine (10), Scott A. Snyder of the University of Chicago cyclized (Angew. Chem. Int. Ed. 2016, 55, 3625. DOI: 10.1002/anie.201510520) the pyrone 8. Overnight stirring with silica gel converted the initial adduct to 9.
Choon-Hong Tan of Nanyang Technological University developed (Chem. Asian. J. 2016, 11, 390. DOI: 10.1002/asia.201500246) an organocatalyst that mediated the enantioselective cyclization of 11. The product 12 was carried on to (+)-α-yohimbine (13).
Gang Liu and Yefeng Tang of Tsinghua University observed (Angew. Chem. Int. Ed. 2016, 55, 6992. DOI: 10.1002/anie.201602439) that the single stereogenic center of the imide 14 was sufficient to direct the cyclization to 15, that was readily carried on to periconiasin A (16). The o-methylbenzoyl N-protecting group was critical for the efficiency of the cycloaddition.
Ming-Hua Qiu of the Kunming Institute of Botany isolated (Org. Lett. 2016, 18, 496. DOI: 10.1021/acs.orglett.5b03473) a novel segetane diterpene, eupesegetanin A (19), from Euphorbia peplus. Following the biosynthetic hypothesis, exposure of the jatrophane derivative 17 to TMEDA led, via 18, to 19.