Direct Cyclopropanation of α‐Cyano β‐Aryl Alkanes by Light‐Mediated Single Electron Transfer Between Donor–Acceptor Pairs

Abstract

Cyclopropanes are traditionally prepared by the formal [2+1] addition of carbene or radical based C1 units to alkenes. In contrast, the one‐pot intermolecular cyclopropanation of alkanes by redox active C1 units has remained unrealised. Herein, we achieved this process simply by exposing β‐aryl propionitriles and C1 radical precursors (N‐oxy esters) to base and blue light. The overall process is redox‐neutral and a photocatalyst, whether metal‐ or organic‐based, is not required. Our findings support that single electron transfer (SET) from the α‐cyano carbanion of the propionitrile to the N‐oxy ester is facilitated by blue‐light via their electron donor–acceptor (EDA) complex. The α‐cyano carbon radical thus formed can then lose a β‐proton to form a π‐resonance stabilised radical anion that preferentially couples at the benzylic β‐position with a decarboxylated C1 radical unit. This new transition metal‐free chemistry tolerates both electron rich and electron deficient (hetero)aryl systems, even sulfide or alkene functionality, to afford a range of cis‐aryl/cyano cyclopropanes bearing congested tetrasubstituted quaternary carbons.

Phenylphenothiazine-Based Porous Organic Polymers as Visible-Light Heterogeneous Photocatalysts for Switchable Bromoalkylation and Cyclopropanation of Unactivated Terminal Alkenes

“…When the monomers PTH-M1 and PTH-M2 were used instead, the reactions delivered higher yields (entries 3–4, Table ). Interestingly, bromoalkylation − and cyclopropanation − products were produced simultaneously. Furthermore, significantly improved conversion was achieved by employing porous materials PTH-POP1 and PTH-POP2 as the catalysts, suggesting polymerization brought enhanced reactivity. − Consistent with the more favorable optical and electronic properties (Figure ), PTH-POP2 gave higher yields of the mixture compared with that of PTH-POP1 (entries 5–6, Table ).…”

Synthesis and styrene copolymerization of novel fluoro and iodomethoxy ring-disubstituted isobutyl phenylcyanoacrylates

“…Fluoro ring-substituted methyl phenylcyanoacrylates (PCA) were cited in such applications as pentanidium-catalyzed direct assembly of vicinal all-carbon quaternary stereocenters through C(sp3)-C(sp3) bond formation [1], as direct cyclopropanation of αcyano β-aryl alkanes by light-mediated single electron transfer between donor-acceptor pairs [2], in synthesis of cyanoacrylates by Knoevenagel condensation [3], in diastereoselective four-component synthesis of polysubstituted 2-piperidinones with three and four stereogenic centers [4], diastereoselective synthesis of spiro [2.3]hexanes from methylenecyclopropane and cyanoalkenes [5], in study of microporous polyurethane material for size selective heterogeneous catalysis of the Knoevenagel reaction [6], in the regio-and stereo-selective synthesis of spiro pyrrolidine and pyrrolizidine derivatives [7], in pyrrolizinone synthesis through functionalized C-alkylpyrroles [8], in synthesis of new pyridinecarbonitriles from fluoro arylpropenones [9], in chiral urea-catalyzed enantioselective epoxidation of α,β-unsaturated esters [10], in green synthetic methodology of (E)-2-cyano-3-aryl selective Knoevenagel adducts under microwave irradiation [11], in syntheses of highly substituted cyclohexanes and cyclopentenes via phosphine-catalyzed chemo-and diastereoselective [2 + 2 + 2] and [3 + 2] annulations of γ-methyl allenoates with doubly activated olefins [12], in studies of carbonyl function switches from reacting to activating in aza-Wittig reaction with nitriles [13], in studies of compartmentalization of incompatible polymers within metal-organic frameworks towards homogenization of heterogeneous hybrid catalysts for tandem reactions [14], in Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids in water [15], in 3 tunable cinchona-based thioureas-catalysed asymmetric epoxidation to glycidic ester derivatives [16], in synthesis and biological evaluation of spiro[acenaphthylene-1,2'pyrrolidine] derivatives as potent anti-infective agents [17]. Iodo ring-substituted styrenic compound is reported in synthesis of aryl nitriles via aerobic oxidative cleavage of aryl C=C Bonds with (NH4)2CO3 as the nitrogen source [18], in a study of the effects of complex structure on aryl iodide oxidative addition at bipyridyl-ligated gold(I) centers [19], as well as synthesis and evaluation of a novel library of alternating amphipathic copolymers to solubilize and study membrane proteins [20].…”

Synthesis and styrene copolymerization of novel alkoxy ring-substituted tert-butyl phenylcyanoacrylates

“…Methoxyphenylcyanoacrylates (MPCA) were reported in a number of studies [1][2][3]. Thus, methyl MPCA was involved in direct cyclopropanation of α-cyano β-aryl alkanes by light-2 mediated single electron transfer between donor-acceptor pairs [1].…”

“…Methoxyphenylcyanoacrylates (MPCA) were reported in a number of studies [1][2][3]. Thus, methyl MPCA was involved in direct cyclopropanation of α-cyano β-aryl alkanes by light-2 mediated single electron transfer between donor-acceptor pairs [1]. Protic ionic liquid methylimidazolium thiocyanate was used as reagent, catalyst, and solvent in synthesis of MPCA [2].…”

“…1 H NMR  8.7 (s, 1H, CH=), 8.4-6.9 (m, 4H, Ph), 3.9 (s, 3H, OCH3), 1.7 (s, 9H, CH3);13 C NMR  162 (C=O), 150 (HC=), 148-111 (Ph), 116 (CN), 104 (C=), 83 (OC), 56 (PhOCH3), 27 (CH3); IR (cm -1 ): 2928 (m, C-H), 2223 (m, CN), 1710 (s, C=O), 1598 (s, C=C), 1267 (s, C-O-CH3), 752 (s, C-H out of plane). Anal.Calcd.…”