Stereoselective Photoredox Catalyzed (3+3) Dipolar Cycloaddition of Nitrone with Aryl Cyclopropane

Abstract

By resorting to the principle of remote activation, we herein demonstrate the first photoredox catalyzed (3+3) dipolar cycloaddition of nitrones with aryl cyclopropanes. Key to the fidelity of the reaction resides in a facile manner of substrate activation by single‐electron transfer (SET) oxidation with photoredox catalysis, and the reaction takes place through a stepwise cascade encompassing a three‐electron‐type nucleophilic substitution triggered cyclopropane ring‐opening and a diastereoselective 6‐endo‐trig radical cyclization manifold. The reaction proceeds under mild conditions with excellent regio‐ and stereoselectivity, nicely complementing the well‐developed Lewis acid catalyzed cycloaddition of donor‐acceptor cyclopropanes. Other merits of the protocol include wide scope of aryl cyclopropanes with diversified substitution patterns and good functional‐group compatibility. A mechanism involving an aryl radical cation promoted remote activation mode was also proposed and supported by mechanistic experiments.

An Intermolecular Hydroarylation of Unactivated Arylcyclopropane via Re2O7/HFIP-Mediated Ring Opening

“…To begin, we chose to evaluate arylcyclopropane 1a with an electron-withdrawing CF 3 group on the phenyl substituent. Unlike D–A cyclopropanes, the absence of a second activating group makes it hard to activate, and the electron-withdrawing group on the aryl group makes it even harder . To our delight, an excellent isolated yield of 95% of hydroarylation product 3a (Table S1, entry 2) was achieved within 12 h with 1 mol % Re 2 O 7 in HFIP − at 40 °C when p -xylene 2a was used as the coupling partner after standard reaction optimization (see section S3 of the Supporting Information), which is even more reactive than 10% TfOH for the same type of substrate.…”

Synthesis of Quinolinoneylnitrones and Coumarinylnitrones via a Cascade Hydroamination and Aza-MBH-Type Reaction

“…With the high-speed development of synthetic chemistry, the public demand for green, rapid, and economical synthesis continues to grow explosively. More tandem/domino/cascade reactions jave been developed for this purpose. − With the help of these efficient devices, many complex biological compounds, including coumarins and quinolinones, have been successfully synthesized. In particular, coumarin compounds make up a class of natural products with aromatic aromas, widely distributed in the natural world .…”