Cerium-Catalyzed Formal Cycloaddition of Cycloalkanols with Alkenes through Dual Photoexcitation

Abstract

We describe a synergistic utilization of cerium photocatalysis and photoinduced electron transfer catalysis that enables an atom- and step-economical ring expansion of readily available cycloalkanols. This operationally simple protocol provides rapid access to privileged and synthetically challenging bridged lactones. The mild catalytic manifold has been adapted to continuous flow for scale-up applications and employed for the concise synthesis of polycyclic core of nepalactones.

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

“…In organic photoredox catalysis, the mechanism of Figure b was put forward to account for the cerium‐ and DPA‐co‐catalyzed reaction between cycloalkanols and alkenes to form bridged lactones (Table , entry 3) . The cerium source is CeCl 3 and excess chloride was used, presumably because this favors the formation of [CeCl 6 ] 3− (M ( n −1)+ in Figure b) instead of [Ce 2 Cl 9 ] 3− .…”

Reductive radical-polar crossover: traditional electrophiles in modern radical reactions

“…In 2018, the group of Zhiwei Zuo reported on a dual ceriumand photoredox-catalysed bridged lactone formation starting from cycloalkanols and Michael acceptors (Scheme 4). 9 At rst, the alkoxy radical is generated through a cerium(IV)-mediated ligand-to-metal charge transfer. Owing to the instability of such radicals, a C-C-b-scission generates a more stabilised alkyl radical.…”

Radical‐Promoted C−C Bond Cleavage: A Deconstructive Approach for Selective Functionalization

“…To address this concern, the authors reported anew dual photocatalytic protocol. [36] Themethodology has allowed aradical cross-coupling with electron-deficient alkenes,which falls outside of the redox window of Ce III to be achieved, thus the strongly reducing photoexcited anthracene catalyst may reduce the alkyl radical. Final SET between the radical cation of anthracene and Ce III enables the closure of both catalytic cycles.…”

“…Under these reaction conditions,t he ring-strain energy is not ap rerequisite to furnishing an efficient b-fragmentation that leads to fragmentation of several ring sizes.The synthetic utility of this strategy is clear since the deconstruction/hydrogenation of complex natural product derivatives such as the hecogenin analogue 15 a,can be attained. [36] Themethodology has allowed aradical cross-coupling with electron-deficient alkenes,which falls outside of the redox window of Ce III to be achieved, thus the strongly reducing photoexcited anthracene catalyst may reduce the alkyl radical. Xia and co-workers also reported as imilar methodology by using white light to achieve either deconstruction/allylation or deconstruction/formylation.…”