Photochemical Hydrothiolation of Amorphadiene and Formal Synthesis of Artemisinin via a Pummerer Rearrangement

A General Photoactive H-Bonding EDA Complex Model Drives the Selective Hydrothiolation and Hydroxysulfenylation of Carbonyl Activated Alkenes

Excitation of photoactive electron donor-acceptor (EDA) complexes to generate radical is a promising approach in radical chemistry. In this study, we introduce a new model of H-bonding EDA complexes for the selective hydrothiolation and hydroxysulfenylation of carbonyl-activated alkenes with diverse thiols under visible light conditions. The reliability of this H-bonding EDA complex model has been confirmed by meticulous experimental and theoretical calculations. Mechanistic investigations have revealed the significant influence of the solvent in determining whether the excitation of photoactive H-bonding EDA complex leads to charge transfer (CT) or energy-charge transfer (En-CT), thereby controlling Markovnikov and anti-Markovnikov selectivity. Notably, the Quantum Theory of Atoms in Molecules (QTAIM) analysis clearly shows that the excited state of the C=O-H-S EDA complex involves closed-shell partially covalent interactions.

Facile Cleavage of Activated Ketones: An Access to Thioethers via In Situ Generation of Anhydrides by Pummerer-Type Rearrangement

Herein, we report an oxygen insertion in activated ketones from simple inorganic carbonates for the synthesis of symmetric aromatic anhydrides. For the first time, Li2CO3 acts as an oxygen source and the in situ generated symmetric aromatic anhydrides undergo Pummerer-type rearrangement to access α-benzoyloxy-thioethers. Attractively, this protocol occurs under metal-, ligand-, and oxidant-free conditions and is compatible with a wide range of substrates. Control experiments reveal the reaction pathway.

PhI(OAc)2-Mediated Regioselective Hydrothiolation of Allenamides with Thiophenol via a Radical Process: Synthesis of Vinyl Sulfides

An efficient PhI(OAc)2-mediated regioselective hydrothiolation of allenamides with thiophenol via a radical process was developed to create a workable route to vinyl sulfides. The reaction exhibits a good functional group tolerance and high efficiency, affording the products in good to excellent yields. Mechanistic investigations indicated that the radical cascade proceeds through an allyl radical intermediate, which is formed via the addition of the PhS radical to the central carbon of allenamides. Moreover, the reaction was also efficient with selenophenol, providing the corresponding product, vinyl selenide, in a 99% yield.

Copper-Catalyzed Regio- and Stereoselective Hydrothiolation of Allenamides, Enamides, and Ynamides

We report a simple protocol for the copper-catalyzed hydrothiolation of N-unsaturated precursors, i.e., allenamides, enamides, and ynamides, under mild conditions. This method proceeds with a low loading of a commercially available Cu(CH₃CN)₄PF₆ catalyst and enables the room-temperature transformation of a wide range of aromatic and aliphatic thiols into allylic or vinylic thioethers, 1,3-dithioethers, and thioaminals with good regio- and stereoselectivity.

Site-Selective Functionalization of Unactivated Allylic C-H Bonds via Direct Deprotonation with KTMP: Application to the Formal Total Synthesis of (+)-Artemisinin from Amorphadiene

The site-selective functionalization of unactivated allylic C-H bonds via direct deprotonation using KTMP is described. The conversion of amorphadiene to artemisinic alcohol via a simple, highly regioselective deprotonation over 4 other possible allylic sites is shown with further extrapolation to the first large-scale telescoped chemical synthesis of artemisinic acid from amorphadiene. Finally, application of the method for the successful site-selective functionalization of unactivated allylic C-H bonds in other terpene-based natural products is also highlighted.

Palladium-Catalyzed Regioselective Allylic Oxidation of Amorphadiene, a Precursor of Artemisinin

A regioselective Pd-catalyzed allylic oxidation of amorphadiene, a key precursor to the antimalarial drug artemisinin, is described. Amorphadiene can be obtained in high yields by fermentation, but it is currently treated as a waste in the industrial semisynthetic artemisinin process. The catalytic step described here is a substitute for the P450 enzymes involved in the artemisinin biosynthesis and opens up new opportunities to supplement a critical step in the current semisynthetic route and increase the potential of the fermentation process.