trans-Diastereoselective Syntheses of γ-Lactones by Visible Light-Iodine-Mediated Carboesterification of Alkenes

[Development of Molecular Transformation Reactions Using Visible Light and Main Group Elements]

Owing to their ability to induce excitation of specific molecular orbitals or initiate chemical reactions, photochemical reactions have the potential to be more effective at selectively activating target molecules than thermal reactions. The thermal reactions transfer thermal energy to activate molecules, which often leads to the activation of multiple molecular species, including undesired ones, resulting in non-selectivity. This nonselectivity may result in undesirable side reactions or decrease reaction efficiency. Additionally, photochemical reactions can induce selective activation by absorbing specific wavelengths of light. However, visible light-driven photocatalytic reactions typically require expensive transition metal catalysts or organic dyes, leaving plenty of room for improvement. To address the aforementioned issues, the photochemical properties of the main group elements, such as halogens, were optimized and methodologies for visible light-induced reactions were developed. Activation of molecular halogen, halogen-carbon bonds, and halogen bonding interactions were independently investigated and various methodologies were reported. These developed reactions are excellent methodologies that use inexpensive raw materials and are thus predicted to contribute significantly toward sustainability.

Direct Oxidation of Aryl Malononitriles Enabling a Copper-Catalyzed Intermolecular Alkene Carbochlorination

A copper-catalyzed carbochlorination of alkenes with aryl malononitriles and chloride is disclosed. This net oxidative transformation proceeds with activated and unactivated alkenes with moderate to excellent yields. Mechanism experiments suggest addition of the malononitrile radical to form a secondary carbon radical which is intercepted by a chloride source. The resultant products can be transformed into biologically important γ-lactones in one further step.

Three-Component Iminolactonization Reaction via Bifunctionalization of Olefins Using Molecular Iodine and Visible Light

A novel three-component γ-iminolactonization reaction was developed, which relied on the C-C/C-O bond-forming bifunctionalization of olefins using molecular iodine and visible light. This strategy did not require any (heavy) metal reagents for double-bond activation because molecular iodine acted as a rare-metal-alternative reagent through visible light irradiation. In addition, the preactivation of amines and other substrates is not required. The mechanistic investigation revealed that the generated iodine radicals under visible light irradiation reacted with alkenes to form a highly reactive intermediate; then, the three-component reaction of diiodide, malonate, and amine furnished iminolactone. Of note, the developed reaction is simple and realized the diversity-oriented synthesis innovative methodology of γ-iminolactone derivatives in drug discovery chemistry.