Efficient Syntheses of Korupensamines A, B and Michellamine B by Asymmetric Suzuki-Miyaura Coupling Reactions

by Guangqing Xu, Wenzhen Fu, Guodu Liu, Chris H. Senanayake and Wenjun Tang_*

Efficient asymmetric Suzuki-Miyaura coupling reactions are employed for the first time in total syntheses of chiral biaryl natural products korupensamine A and B in combination with an effective diastereoselective hydrogenation, allowing ultimately a concise and stereoselective synthesis of michellamine B. Chiral monophosphorus ligands L1–3 are effective for the syntheses of a series of functionalized chiral biaryls by asymmetric Suzuki-Miyaura coupling reactions in excellent yields and enantioselectivities (up to 99% ee). The presence of a polar-π interaction between the highly polarized BOP group and the extended π system of arylboronic acid coupling partner is believed to be important for the high enantioselectivity.

Journal of the American Chemical Society

Publication Date (Web): October 22, 2013

DOI: 10.1021/ja409669r

Organoytterbium Ate Complexes Extend the Value of Cyclobutenediones as Isoprene Equivalents

by Emma Packard, David D. Pascoe, Jacques Maddaluno, Théo P. Gonçalves, David C. Harrowven*

Changing course: While organolithium and Grignard reagents favor addition to C1 of A (R=Me), the corresponding organoytterbium reagents add to C2 (R=tBu). Computational studies provide insights into the nature of organoytterbium species and their reactivity, and a total synthesis of (−)-mansonone B illustrates the utility of the method in terpenoid synthesis. Tf=trifluoromethanesulfonyl.

Angewandte Chemie Internation Edition

Article first published online: 23 OCT 2013

DOI: 10.1002/anie.201307193

Total Synthesis and Structural Revision of the Alkaloid Incargranine B

by Patrick D. Brown, Anthony C. Willis, Michael S. Sherburn, Andrew L. Lawrence*

Seeing double: Consideration of the biosynthetic origins of incargranine B, which was originally assigned an unprecedented indolo[1.7]naphthyridine structure, led to the proposal of a dipyrroloquinoline framework as a more biosynthetically feasible structure (see scheme; Piv=pivaloyl). This hypothesis was validated by a short biomimetic synthesis of incargranine B.

Angewandte Chemie Internation Edition

Article first published online: 24 OCT 2013

DOI: 10.1002/anie.201307875

Rapid Access to Spirocyclic Oxindole Alkaloids: Application of the Asymmetric Palladium-Catalyzed [3 + 2] Trimethylenemethane Cycloaddition

by Barry M. Trost*, Dustin A. Bringley, Ting Zhang and Nicolai Cramer

The marcfortines are complex secondary metabolites that show potent anthelmintic activity and are characterized by the presence of a bicyclo[2.2.2]diazaoctane fused to a spirooxindole. Herein, we report the synthesis of two members of this family. The synthesis of marcfortine B utilizes a carboxylative TMM cycloaddition to establish the spirocyclic core, followed by an intramolecular Michael addition and oxidative radical cyclization to access the strained bicyclic ring system. In addition, the first asymmetric synthesis of (−)-marcfortine C is described. The key step involves a cyano-substituted TMM cycloaddition, which proceeds in nearly quantitative yield with high diastereo- and enantioselectivity. The resulting chiral center was used to establish all remaining stereocenters in the natural product.

Journal of the American Chemical Society

Publication Date (Web): October 1, 2013

DOI: 10.1021/ja409013m