Catalytic Radical‐Polar Crossover Non‐Classical Semipinacol Rearrangements: The Sustainable Approach

Abstract

Semipinacol rearrangement has brought several elegant methods for the rapid synthesis of various complex scaffolds and as a result, has been applied extensively in the total synthesis of natural products. Apart from the classical ways, where transition metal or acids catalyzes the formation of carbocation, the semipinacol rearrangement has seen numerous revolutions and now are being happening in an eco-friendly manner relying on a catalytic radical-polar crossover tool. These catalytic processes are mainly occurring through photocatalysis or electrocatalysis. This review will provide a brief idea of these developments. 1. Introduction 2. Photocatalytic Radical-Polar Crossover 3. Electrocatalytic Radical-Polar Crossover 4. Metal-Free Radical-Polar Crossover 5. Conclusion and Outlook

Advances in photoinduced radical–polar crossover cyclization (RPCC) of bifunctional alkenes

“…Previous review articles about photoinduced radical–polar crossover reactions mainly dealt with outlining radical–polar crossover, and no reviews before this one have aimed to highlight the significance of logical bifunctional alkene design in the area of radical polar crossover for cyclic product construction. 4…”

“…In this review, a focus will be placed on representative transformations involving typical bifunctional alkenes as readily available building blocks through radical–polar crossover cyclizations to form the desired structurally diverse cyclic products through dislodging the tethered leaving group (LG), trapping by a nucleophile or electrophile, or other reaction types (Scheme 1). It is noteworthy that radical–polar crossover reactions in the field of photoredox catalysis are mentioned in only a few reviews, 4 which emphasize transformations in which both radical and ionic intermediates were involved in the reaction pathways; however, no review has sought to highlight the interesting and key roles of bifunctional-alkene-mediated radical–polar crossover for the construction of cyclic compounds in a net-neutral manner.…”

Radical-triggered base-free 1,3-C → C migrations: chemodivergent synthesis of cyclic imines from N-allyl enamines

“…20 Moreover, 1,3-alkyl migrations of allylic alcohols were achieved via a light-driven proton-coupled electron transfer (PCET) strategy, 21 in which a Brønsted-Lowry base was necessary for the homolytic activation of the O-H bond to generate a reactive alkoxy radical intermediate (Scheme 1c). Although progress has been achieved in 1,3-carbon migrations, more diverse 1,3- In recent years, radical-mediated rearrangement reactions, [22][23][24][25][26] which proceed via cationic or radical pathways, for example, the [1,2]-rearrangements of allylic alcohols (semipinacol rearrangements), [27][28][29] have proved to be a unique class of organic transformations. However, anionic ones for 1,3-C → C migrations are far from being developed.…”

“…In recent years, radical-mediated rearrangement reactions, 22–26 which proceed via cationic or radical pathways, for example, the [1,2]-rearrangements of allylic alcohols (semipinacol rearrangements), 27–29 have proved to be a unique class of organic transformations. However, anionic ones for 1,3-C → C migrations are far from being developed.…”

A Domino Radical Amidation/Semipinacol Approach to All‐Carbon Quaternary Centers Bearing an Aminomethyl Group

“…The semipinacol rearrangement provides an important strategy for accessing all‐carbon quaternary centers [8–11] . In recent years, numerous groups have reported photoredox‐mediated radical addition/semipinacol rearrangement sequences that enable the construction of all‐carbon quaternary centers under mild conditions (Figure 2a).…”