Reductive Radical Annulation Strategy toward Bicyclo[3.2.1]octanes: Synthesis of ent-Kaurane and Beyerane Diterpenoids

Abstract

Here we report a general [3 + 2] radical annulation that allows the facile construction of bicyclo[3.2.1]octane motifs in ent-kaurane-and beyerane-type diterpenoids. This radical annulation is difficult to control but was realized by harnessing an unprecedented and counterintuitive effect of TEMPO. Eleven natural products with a wide array of oxidation states are easily prepared, demonstrating the powerful utility of this straightforward synthetic strategy.

Catalyst- and solvent-free regioselective ring opening of aziridines with amines: application in the gram-scale synthesis of the α,β-diamino propionic derivative, aspergillomarasmine A

“…More importantly, this substrate provided more approaches for the deprotection of benzyl in synthesizing α,β-diamino propionic derivatives, such as catalytic hydrogenation 18 and basic hydrolysis. 19 It was worth mentioning that the crystal structure of 3ca (Table 5) further confirmed the regioselectivity and the chirality maintenance of the products.…”

Recent Progress on Transition-Metal-Mediated Reductive C(sp3)–O Bond Radical Addition and Coupling Reactions

“…Very recently, Li and co-authors developed a radical addition/cyclization protocol to access strained, bridged bicyclo frameworks using a similar MgCl 2 /PBI/Zn reductive approach (Scheme 20). 46 The engagement of TEMPO, which can be transformed into TEMPO-H and/or Zn(TEMPO) 2 in situ and then quenches the final secondary radical, as an additive proved to be crucial for the transformation. The authors successfully constructed several bicyclo[3.2.1]octane motifs of ent-kaurane-type diterpenoids and a beyeranetype diterpenoid.…”

Diastereoselective Synthesis of Bicyclo[3.2.1]octanes via Catalyst‐Free Cascade Michael/Henry Reaction with a Functionalized Vinylogous Nucleophile

“…Meanwhile, great efforts have been devoted to accessing this class of compounds via organocatalysis in an enantioenriched manner, such as Michael/Henry [10] and Michael/ aldol [11] domino reactions. In recent elegant reports, acid or base-promoted annulation protocols, [12] together with electrochemical and radical cycloaddition strategies, [13] allowed access to bicyclo[3.2.1]octane frameworks as well. Nevertheless, the non-negligible drawbacks associate with the current methodologies, and in many cases, tedious multi-step conversions are required to obtain the reaction precursors.…”