Rearrangement and Cyclization Reactions by Photoinduced Electron Transfer: New Approaches for the Synthesis of Polycyclic Compounds

Abstract

The concept of intramolecular radical ion cyclization reactions by photoinduced electron transfer (PET) is a powerful tool for constructing complex carbocyclic and heterocyclic ring systems. In this account we describe our earlier investigations in this field followed by the development of new approaches to the synthesis of polycyclic compounds. Radical ions generated by single-electron transfer (SET) from suitable neutral molecules are used as decisive intermediates in a wide range of interesting cyclization processes and reactions. Various synthetic strategies are presented involving radical anionic or radical cationic species generated by reductive and oxidative PET, respectively. 1 Introduction 2 General Concept 3 Reductive Electron Transfer: Formation of Ketyl and g-Keto Radicals 4 Oxidative Electron Transfer: Formation of a-and b-Keto Radicals 5 Su mmary

Total Synthesis with Gram-Scale Radical Process: An Inspiration for Pharmaceutical Industry

“…The tricyclic core 80 was formed in 77% yield on a 1-g scale. In this cascade reaction, a PET process could yield a cationic radical 79-I that undergoes a 6-endo-trig cyclization to produce a radical 79-II . Subsequently, intramolecular capture of the radical by an alkyne occurred in a 5-exo-dig fashion, leading to the formation of the tricyclic product 80 which was then advanced via a five-step process that consisted of introducing the cyclized side chain and enone moiety to 81 .…”

“…While several research groups have disclosed reports on the total synthesis of C-20 oxygenated ent-kaurane diterpenoids, 41 the completion of sculponin U (77) has only been described by our group. 42 Herein, we will highlight our synthesis of sculponin U (77) through a photoinduced radical cascade cyclization process (Scheme 8). The synthesis began with the preparation of enone 78 using a two-step protocol starting from commercially available materials.…”

A Photoinduced Radical Cascade Cyclization for the Synthesis of Angularly Fused Tricyclic Compounds

“…With this in mind, we propose a plausible mechanistic pathway for the radical cascade (Scheme ). Upon single-electron transfer (SET) from enol silyl ether 1a to DCA/Phen./ hv , a radical cation i is formed, which is subsequently deprotected by MeOH, resulting in α-carbonyl radical ii . The following 5-exo-dig cyclization of radical ii gives rise to species iii or iv .…”