Visible-Light-Mediated, Diastereoselective Epimerization of Exocyclic Amines

Switchable Enantio- and Diastereoselective Michael Additions of β-Keto Amides to Nitroolefins: Crystallization-Based Inversion of Kinetic Stereocontrol

Asymmetric catalytic reactions rely on chiral catalysts that induce highly ordered transition states capable of imparting stereoselectivity in the bond-forming step(s). Productive deviations from this paradigm are rare yet hold the potential for accessing different stereoisomers using the same catalyst. Here, we present an enantio- and diastereoselective Michael addition of β-keto amides to nitroolefin electrophiles proceeding via an unusual scenario where the kinetic diastereocontrol imparted by the catalyst may be overridden by crystallization to provide the complementary stereoisomer of the product.

Total Synthesis of Putative Melognine

Total synthesis of melognine was accomplished. A 10-membered cyclic alkyne was prepared via an intramolecular SN2 reaction of a nosylamide. Enyne metathesis of the cyclic alkyne under an atmosphere of ethylene afforded a 1,3-diene. Intramolecular cycloaddition of a nitrone and an azomethine ylide with the 1,3-diene moiety constructed the characteristic highly fused skeleton. Further transformation, including ring-closing metathesis, resulted in the synthesis of melognine, whose NMR spectra did not match the reported data. Close inspection of the spectra of melognine in the literature suggested that the structure of melognine might be identical with that of a known alkaloid, melodinine L.

Remote C-H Amination and Alkylation of Camphor at C8 through Hydrogen-Atom Abstraction

Camphor continues to serve as a versatile chiral building block for chemical synthesis. We have developed a novel method to functionalize the camphor skeleton at C8 using an intramolecular hydrogen atom abstraction. The key advance involves the use of a camphor-derived aminonitrile, which is converted to the corresponding nitrogen-centered radical under photoredox conditions to effect the 1,5-hydrogen atom transfer at C8. The resulting carbon-centered radical at C8 was utilized in a C-H amination to access topologically complex proline derivatives. Furthermore, the total synthesis of several sesquiterpenoids was accomplished by engaging the radical generated at C8 in alkylation reactions.