Remote Giese Radical Addition by Photocatalytic Ring Opening of Activated Cycloalkanols

Abstract

The application of proton coupled electron transfer (PCET) processes in organic synthesis has opened the door to new radical intermediates for synthesis such as alkyl radicals in remote positions to a ketone. Herein, we present the addition of these remote alkyl radicals to electron deficient double bonds under photoorganocatalyzed and very mild conditions. The method is not only applicable to diactivated double bonds, but monoactivated ones are also accessible using more stabilized alkyl radicals, and alkyl chains of any length can be introduced. The final products can be easily converted into more complex structures via a one‐pot process, and the activating functional groups were transformed in the more versatile methyl esters. Mechanistic investigations support a mechanistic proposal based on a PCET process.

TEMPO-Mediated Interrupted 6π-Photocyclization of ortho-Biaryl-Appended 1,3-Dicarbonyl Compounds toward 10-Phenanthrenols

“…The reaction starts with the direct irradiation of the mixture of keto-1a and enol-1a isomers with violet light (λ = 390−395 nm), the isomers absorb light energy and are immediately excited to its singlet excited state followed by ISC to its triplet excited state 3 1a*. The triple excited state 1a undergoes classical 6π electrocyclization, which produces transients 1,4-diradical A and B 26 similar to the de Mayo reaction, 27 and then trapped by tandem TEMPO-mediated direct HAT 22,28 or Cope-like elimination 29 by losing TEMPOH to give the desired product 2a.…”

Ring‐Opening Functionalization/Cyclization Reactions of Cycloalkanols under Transition‐Metal‐Free Conditions

“…Soon after, Marzo, Alemán and co‐workers reported the addition of distal carbonyl alkyl radical generated by photocatalytic ring‐opening of various sizes cycloalkanols to electron deficient alkenes under metal‐free conditions (Scheme 3). [13] This method featured good functional group compatibility, broad substrate scope and available for late stage diversification of natural products. Remarkably, the products could be transformed into highly functionalized scaffolds via a one‐pot process, and the activating groups easily converted into the more versatile methyl esters under oxidative conditions.…”

Photoinduced Generation of Active Intermediates from Unmodified 1,3‐Dicarbonyl Compounds for Organic Transformations

“…The photochemical reaction of β‐diketones and double bonds under UV irradiation is referred to as the de Mayo reaction [46] . In 1962, Paul Jose de Mayo reported that the enol form of 1,3‐diketones could undergo a [2+2] cycloaddition reaction with alkenes under UV irradiation, yielding a cyclobutanol intermediate.…”