Part I: Cobalt-catalyzed C–H benzylation of arenes. Part II: Hypervalent iodine-mediated rearrangement of propargylic alcohol

• Main Author: Laskar Roshayed Ali
• Other Authors: Chiba Shunsuke
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Science::Chemistry
• Online Access: https://hdl.handle.net/10356/152289
• Institution: Nanyang Technological University

1,1-Diarylmethanes represent as integral structural moieties that are present in pharmaceutical and biologically active molecules. Thus, the synthetic community has been continuously searching for an efficient and practical method to access these scaffolds. In this regard, a synthetic protocol utilizing directing-group assisted arene C–H functionalization represents an attractive alternative to traditional methods because of the atom- and step-economy of the process as well as controllable regioselectivity. Particularly, C–H benzylation using benzylic electrophile has been well explored using either precious 4d/5d-transition metal-based catalytic system or earth-abundant and cheap 3d-transition metal-based system. Among the first-row transition metals, cobalt-based catalytic systems showed the capabilities to emulate the reactivity of its higher congener congeners as well as distinct reactivity. With the above background, Chapter 1 describes a brief review of a different kind of C–H functionalization reactions that have been achieved using low-valent cobalt-based systems. Building on this background, Chapter 2 is mainly focused on what are the traditional approaches to access diarylmethanes and how we used the directed C–H functionalization approach using a low-valent cobalt system to synthesize diarylmethanes. In our developed synthetic protocol, we used benzylic phosphates and pivalophenone N–H imines as starting materials, and a cobalt salt-ligand-Grignard reagent based catalytic system to successfully prepare diarylmethane derivatives under room-temperature conditions. Chapter 3 and Chapter 4 of the thesis deal with completely different chemistry. In Chapter 3, a glimpse of the recent development of cyclic hypervalent iodine reagents and their applications in synthetic organic chemistry is described with special focus on the heteroaryl- and vinyl-benziodoxol(on)es. Benziodoxol(on)es (BX) are generally bench-stable polyvalent iodine compounds bearing 5-membered heterocyclic scaffolds where the iodine atom is part of the ring. Some of this type of compounds have already proved to serve as useful group transfer reagents, and much effort has been devoted to the development of new BX-type reagents to expand the scope of transferable groups, including aryl and vinyl groups. Chapter 4 shows how we synthesized a novel class of vinyl-benziodoxole derivatives starting from easily accessible propargylic alcohols and benziodoxole triflate using the concept of century-old Meyer-Schuster rearrangement. These vinyl-BXs are air-stable, easy to handle, and have already proven to act as enone building blocks for traditional cross-coupling reactions.