140.Retro-metal-ene versus retro-Aldol: mechanistic insight into Rh-catalysed formal [3+2] cycloaddition

Song Liu, Tao Zhang, Lei Zhu, Kangbao Zhong, Jianxian Gong, Zhen Yang*, Ruopeng Bai*, Yu Lan*

Chem. Commun., 2018,54(96), 13551-13554

Theoretical calculations have been performed to investigate the mechanism and stereoselectivity of rhodium-catalysed intramolecular [3+2] cycloaddition for construction of a substituted hexahydropentalene complex. A new C–C bond cleavage mechanism, retro-Aldol-type, is proposed and verified for this Rh-catalysed [3+2] cycloaddition reaction.

139.Concise gram-scale synthesis of Euphorikanin A skeleton through a domino ring-closing metathesis strategy

Linlin Shi, Yingdong He, Jianxian Gong *, Zhen Yang *

Chem. Commun. 2020, Advance Article

Euphorikanin A is a diterpenoid possessing a highly congested and unprecedented 5/6/7/3-fused tetracyclic ring skeleton. To access the challenging chemical structure of Euphorikanins, an efficient total synthetic approach is described. The stereoselective synthesis of the core structure of Euphorikanin A has been achieved from a simple dienyne building block, and a domino ring-closing metathesis (RCM) strategy was used for the gram-scale synthesis of the highly strained Euphorikanin A core. This paves the way for the synthesis of structurally diverse Euphorikanins.

138.Asymmetric Total Synthesis of Pre-schisanartanin C

Yan-Long Jiang, Hai-Xin Yu, Yong Li, Pei Qu, Yi-Xin Han, Jia-Hua Chen*, Zhen Yang*

J. Am. Chem. Soc. 2019, JUST ACCEPTED

Pre-schisanartanin C belongs to the family of Schisandra nortriterpenoids with potent antihepatitis, antitumor, and anti-HIV activities. This paper presents the enantioselective total synthesis of pre-schisanartanin C (1). An important step in the total synthesis of 1 is gold-catalyzed intramolecular cyclopropanation of an 1,8-enyne substrates bearing a secondary ester group at the propargylic position to prepare a bicyclo[6.1.0]nonane core. Additional highlights include i) an asymmetric Diels–Alder reaction to install the initial C5 stereogenic center of 1, and ii) a sequential Pd-catalyzed Stille coupling, regio- and stereo-selective Sharpless asymmetric dihydroxylation, and a subsequent intramolecular lactonization to contruct the side chain of 1. The developed chemistry paves the way for the total syntheses of other family members bearing highly rigid bicyclo[6.1.0]nonane cores.

137.Asymmetric Total Synthesis of (−)-Pavidolide B via a Thiyl-Radical-Mediated [3 + 2] Annulation Reaction

Pengpeng Zhang, Yuanhe Li, Zhiming Yan, Jianxian Gong*, Zhen Yang*

J. Org. Chem. 2019, 84(24), 15958-15971

The development of an efficient strategy for the asymmetric total synthesis of the bioactive marine natural product (−)-pavidolide B is described in detail. The development process and detours leading to the key thiyl-radical-mediated [3 + 2] annulation reaction, which constructed the central C ring with four contiguous stereogenic centers in one step, are depicted. Subsequently, the seven-membered D ring is constructed via a ring-closing metathesis reaction followed by a Rh(III)-catalyzed isomerization. This strategy enables the total synthesis of (−)-pavidolide B in the longest linear sequence of 10 steps.

136.Diastereoselective Construction of All-Carbon Quaternary Stereocenters via Intramolecular Oxidative Cross-Coupling Reaction

Wei Chen, Renyu Guo, Jianxian Gong*, Zhen Yang*

Chin. J. Org. Chem. 2019, 39 (1), 238-248

The formation of sterically hindered C—C bond represents a great challenge in modern synthetic organic chemistry. A particularly challenging issue is the construction of all-carbon quaternary stereocenters. Herein, a ceric ammonium nitrate (CAN)-mediated intramolecular oxidative cross-coupling of silyl ethers for direct construction of valuable polycyclic scaffolds is described. The reaction enables sterically congested vicinal all-carbon quaternary and tertiary stereocenters to be installed diastereoselectively. The developed method provides a concise and efficient approach for ligation of two different segments through a compact C—C bond formation, which has potential applications in the synthesis of com plex molecules as well as sterically congested natural products.