Partnering Photochemical Protocols With Anion Relay Chemistry: Application In The Total Synthesis Of Natural Products

Yifan Deng, University of Pennsylvania

Abstract

Anion Relay Chemistry (ARC), a multi-component union tactic, permits rapid assembly of linear and cyclic fragments. Partnering photochemical protocols with Anion Relay Chemistry can provide diverse reaction pathways and as such considerably extends this construction paradigm. The development of new cascade reactions via photochemistry is represented in this thesis, in conjunction with the application in the total synthesis of polycyclic natural products. Chapter 2 describes the development of an oxidative Brook rearrangement, achieved by single-electron oxidation of hypervalent silicate intermediate. Initiated by a weak base, the resulting carbon radical can engage in conjugate additions to form alkylated adducts or in radical couplings to form C(sp3)-C(sp2) bonds, both in very mild conditions. Chapter 3 describes the generation of dithianyl or dioxolanyl radicals via [1,5]- or [1,6]-hydrogen atom transfer (HAT). This radical relay tactic enables remote C(sp3)-H functionalization to access synthetically challenging 1,4,7-polyol and spiroketal segments, and in turn, has been exploited as the key synthetic transformation in the total synthesis of danshenspiroketallactones. Chapter 4 presents the first total synthesis of (+)-peniciketals A and B. In this synthesis, a Type I ARC tactic was employed to construct the benzo-fused spiroketal skeleton and a late-stage photoisomerization/cyclization union tactic was developed to access the benzo-fused [3.3.1]-none core. This photochemical protocol discovered in the Smith Laboratory further proves to be a powerful tool to synthesize polycyclic structures, showcased in the 3-step total synthesis of (-)-diocollettines A.