Photoredox-catalyzed oxo-amination of aryl cyclopropanes

Abstract

Cyclopropanes represent a class of versatile building blocks in modern organic synthesis. While the release of ring strain offers a thermodynamic driving force, the control of selectivity for C–C bond cleavage and the subsequent regiochemistry of the functionalization remains difficult, especially for unactivated cyclopropanes. Here we report a photoredox-coupled ring-opening oxo-amination of electronically unbiased cyclopropanes, which enables the expedient construction of a host of structurally diverse β-amino ketone derivatives. Through one electron oxidation, the relatively inert aryl cyclopropanes are readily converted into reactive radical cation intermediates, which in turn participate in the ensuing ring-opening functionalizations. Based on mechanistic studies, the present oxo-amination is proposed to proceed through an SN2-like nucleophilic attack/ring-opening manifold. This protocol features wide substrate scope, mild reaction conditions, and use of dioxygen as an oxidant both for catalyst regeneration and oxygen-incorporation. Moreover, a one-pot formal aminoacylation of olefins is described through a sequential cyclopropanation/oxo-amination.

Radical 1,3-Difunctionalization of Allylboronic Esters with Concomitant 1,2-Boron Shift

“…22 Finally, diastereoselective trapping with the alkynyl triflone leads to the stereoisomer 3w. The selectivity of the alkynylation step can be understood considering the A [1,3] model, 22,23 where the bulky Bpin moiety steers the triflone to react from the opposite site.…”

“…Along these lines, cyclopropanes would be obvious reaction partners, but because of their low reactivity toward radical s-bond cleavage alkyl radicals do not engage in the cyclopropane ring-opening processes. 2,3 However, highly strained [1.1.1]propellanes and bicyclo[1.1.0]butanes can act as radical acceptors leading to 1,3-difunctionalized compounds. [4][5][6][7][8][9] Herein, we introduce an unprecedented approach for the 1,3-difunctionalization of alkenes by using allylboronic esters as radical acceptors.…”

Electrochemical C−C bond cleavage of cyclopropanes towards the synthesis of 1,3-difunctionalized molecules

“…However, in most cases, its large scalability application was not studied and arylcycropropanes with electron-withdrawing groups could not be well compatible due to their high oxidative potential (Fig. 1a) [20][21][22][23][24] .…”

Electrochemical C-C Bond Cleavage of Cyclopropanes towards the Synthesis of 1,3-Difunctionalized Molecules

“…Tri uoromethyl and oxytri uoromethyl substituted arylcyclopropanes gave the corresponding products in 49% and 53% yields, respectively (21)(22). TMS group was retained in this transformation with 52% yield (23). Alkyl group such as tert-butyl group underwent the reaction in lower yield of 40% (24).…”

“…However, in most cases large scalability aplication was not studied, and arylcycropropanes with electron-withdrawing groups could not be well compatible due to high oxidative potential of electron-withdrawing groups substituted arylcycropropanes ( Figure 1a). [20][21][22][23][24] Organic electrochemistry is reviving due to the ease of scalability, the avoidance of stoichiometric oxidizers or reducing agents, and exible reaction tunability. [25] Various redox reactions have been achieved by the comsumption of traceless electrons under constant potential or current conditions.…”