Recent Advances in Visible‐Light‐Driven Photocatalyzed γ‐Cyanoalkylation Reactions

Abstract

Visible-light-induced photoredox-catalyzed organic transformations through single-electron-transfer pathways have recently come to the limelight in modern organic chemistry. These innovative radical processes appear as ideal tactics for making a diverse set of pharmacologically and synthetically useful organic molecules under sustainable conditions. In this review, we summarize a brief overview of recent status of radical C(sp3)À X (X=C, S, Se, B, F, Cl etc) cross-coupling reactions of cyclobutanone oxime esters as the surrogates of γ-cyanoalkyl radicals with various kinds of radical acceptors using photocatalysts irradiated by visible light or natural sunlight. The efficiency of various metal-salts (Ir, Ru, Cu, Pd etc) and metal-free organic molecules (eosin Y, rose Bengal, 4CzIPN, HE, PhPTZ, MesÀ Acr + etc) as photocatalysts were thoroughly examined for the above conversions. Furthermore, the mechanism of the said reactions has also been presented. Notably, the described photocatalytic cycles would further bestow a new mechanistic concept for aiming a variety of cyanoalkylated scaffolds.

Lewis Acid-Catalyzed Remote Site-Selective Ring Deconstruction of Cyclobuteno[a]naphthalene-4-ones to Access Unsymmetric 1,1-Diarylated Olefins

“…Catalytic deconstruction of small-ring compounds involving the cleavage of a strained C–C σ-bond has become the focus of recent research interest and poses a truly difficult challenge in organic synthesis, probably due to the intrinsic low polarity of unactivated carbon–carbon single bonds and the high difficulty in controlling the regioselectivity . Based on the unique reactivity of three- and four-membered rings with tension, various elegant catalytic ring deconstruction reactions have been reported, enabling direct creation of substantially valuable molecular frameworks not available from other methods, together with total atom economy parameters .…”

Recent Advances in Molecule Synthesis Involving C-C Bond Cleavage of Ketoxime Esters

“…Typically, oxime ester derivatives generate imino radicals under the action of photocatalysts or transition metals, and then further convert into carbon-centered radicals (CCRs). The conversion from NCRs to CCRs mainly involves the following methods ( Scheme 1 a): (1) 1,3-hydrogen transfer process to give α -imidoyl carbon radicals (path I) [ 23 , 24 ]; (2) 1,5-hydrogen transfer process to generate a γ -imidoyl carbon radicals (path II) [ 25 , 26 ]; (3) intramolecular addition of an iminyl radical to a tethered alkene or alkyne in a 5- exo -trig or 5- exo -dig fashion (path III) [ 27 , 28 , 29 ]; and (4) intramolecular carbon–carbon bond cleavage to generate carbon radicals (path IV) [ 30 , 31 , 32 ].…”

“…Subsequently, path II and III on photocatalytic cross-couplings via the cleavage of N–O bonds were described in the review by Fu and Zhu [ 34 ]. Recently, both the Zhou [ 31 ] and Samanta [ 32 ] groups presented detailed summaries of the mechanisms, as well as reaction forms, of the various reactions in which cyclic ketoximes are involved. In addition, numerous chemistry groups, including Zard [ 8 ], Chen [ 35 ], Xu [ 36 ], etc., have more or less summarized strategies for the above forms of nitrogen radical centers.…”

“…The nitriles by-products are formed when using acyl oxime esters in reactions. The acyl radicals and cyanoalkyl radicals can be captured by various free radical receptors and participate in various forms of reactions [ 31 , 32 , 37 , 38 , 39 ]. In this review, various free radical reactions involving acyl esters and cyclic ketoxime esters are summarized, and they are classified according to different types of reactions, mainly including radical addition, cross-coupling and radical coupling.…”

Visible-light promoted cascade cyanoalkylsulfonylation/ipso-cyclization ofN-arylpropiolamides toward sulfonated spiro[4,5]trienonesviaSO2insertion

“…In the past decade, cyclobutanone oxime esters have been employed to synthesize functionalized nitriles via iminyl radicals. 7,8 Notably, iminyl radicals generated from cyclobutanone oxime esters can be captured by SO 2 to form cyanoalkylsulfonyl radicals. 9 In 2019, Volla and Liu independently developed a visible-light promoted one-pot synthesis of sulfonated spiro[4,5]trienones from anilines and diaryliodonium salts via SO 2 insertion under transition metal-free conditions.…”