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Monday, August 20, 2012
Douglass F. Taber
University of Delaware

Organocatalytic Carbocyclic Construction: The You Synthesis of (-)-Mesembrine

Frank Glorius of the Universität Münster devised (Angew. Chem. Int. Ed. 2011, 50, 12626. ) a catalyst for the enantioselective acylation of a cyclopropene 1 to the ketone 3. Geum-Sook Hwang of Chungnam National University and Do Hyun Ryu of Sungkyunkwan University effected (J. Am. Chem. Soc. 2011, 133, 20708. ) the enantioselective addition of the diazo ester 5 to an α,β-unsaturated aldehyde 4 to give the cyclopropane 6.

We showed (J. Org. Chem. 2011, 76, 7614. ) that face-selective allylation of an α-iodo enone 7 followed by Suzuki coupling and oxy-Cope rearrangement delivered the cyclopentanone 9. Karl Anker Jørgensen of Aarhus University combined (Org. Lett. 2011, 13, 4790. ) two organocatalysts to effect the addition of 11 to an α,β-unsaturated aldehyde 10, leading to the cyclopentenone 12. Tomislav Rovis of Colorado State University also used (Chem. Sci. 2011, 2, 1835. ) two organocatalysts to condense 13 with 14, to give the cyclopentanone 15. Gregory C. Fu, now at CalTech, found (J. Am. Chem. Soc. 2011, 133, 12293. ) that both enantiomers of the racemic allene 16 combined with 17 to give the cyclopentene 18 in high ee.

Piotr Kwiatkowski of the University of Warsaw found (Org. Lett. 2011, 13, 3624. ) that under elevated pressure (8-10 kbar), enantioselective conjugate addition of nitromethane proceeded well even with a β-substituted cyclohexenone 19. Marco Bella of the Università di Roma observed (Adv. Synth. Catal. 2011, 353, 2648. ) remarkable diastereoselectivity in the addition of the aldehyde 22 to an activated acceptor 21. Following the procedure of List, Jiong Yang of Texas A&M University cyclized (Org. Lett. 2011, 13, 5696. ) 24 to 25 in high ee. Bor-Cherng Hong of National Chung Cheng University described (Synthesis 2011, 1887. ) the double Michael combination of 26 with 27 to give 28 in high ee.

Observing a secondary 13C isotope effect only at the β-carbon of 30, Li Deng of Brandeis University concluded (Chem. Sci. 2011, 2, 1940. ) that the addition to 29 was stepwise, not concerted. In contrast, the cyclization of 32 to 33 reported (Org. Lett. 2011, 13, 3932. ) by Tadeusz F. Molinski of UC San Diego likely was concerted.

En route to (-)-Mesembrine (36), Shu-Li You of the Shanghai Institute of Organic Chemistry prepared (Chem. Sci. 2011, 2, 1519. ) the prochiral cyclohexadienone 34. Kinetic organocatalyzed cyclization to 35 proceeded in high ee.

D. F. Taber, Org. Chem. Highlights 2012, August 20.
URL: https://www.organic-chemistry.org/Highlights/2012/20August.shtm