Oxidative radical cyclizations of malonate enolates induced by the ferrocenium ion – a remarkable influence of enolate counterion and additives

Abstract

To generalize oxidative radical cyclizations of malonate enolates induced by recyclable single electron transfer (SET) oxidant ferrocenium hexafluorophosphate 1, the reactivity of a series of enolates 3 that differ only in their counterions was studied. Only lithium enolates were oxidized by 1, irrespective of their generation method. The presence of amines in stoichiometric or substoichiometric amounts is necessary for SET oxidation-bicyclization of Na, K, Mg, Zn, Si, or Ti enolates 3. The nucleophilicity of 3, the amine, and the presence of halide ions determine the bicyclization yield of lactone 7.

Anticancer Molecule Discovery via C2-Substituent Promoted Oxidative Coupling of Indole and Enolate

“…Furthermore, to figure out whether this oxidative coupling went through Fe- or Li-chelated or non-chelated procedure (Richter et al., 2007, Casey and Flowers, 2011), different base (MHMDS, M = Li, Na, K, and LDA) and Fe(III)-oxidants were probed. All MHMDS afforded nearly the same results except evident lower yield from LDA (Jahn and Hartmann, 2001). Much inferior efficiency was observed with Fe(acac) 3 bearing strong ligand, and only low yield of dimmer of ( R )-carvone ( 3-1 ) was isolated in the presence of non-cheating [FeCp 2 ]PF 6 along with trace amount of 6-1 .…”

Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions

“…Potassium hexamethyldisilazide could also be used as ab ase ( Table 1, entry 2). [16] 2,3-cis-Cyclopentane derivatives 8 and 9 were detected only in some cases ( Table 1, entries 1 , 2, 4, and9 ). If 4pentenoates 1 are substituted at the 5-position, as in 1c-f,diastereomers 6 and 7 weref ormed as the predominant products, both with 2,3-trans orientation of the substituents but with different configurations at the 5position( Ta ble 1, entries 4-7).…”

“…The reactions of the ( Z )‐enolates of esters 1 a , b bearing a terminal alkene unit with Michael acceptors 2 A – C provided cyclic products 6 a , b , g , h in moderate to good yields and good diastereoselectivity (Table 1, entries 1–3, 8, and 9). Potassium hexamethyldisilazide could also be used as a base (Table 1, entry 2) 16. 2,3‐ cis ‐Cyclopentane derivatives 8 and 9 were detected only in some cases (Table 1, entries 1, 2, 4, and 9).…”

Synthesis of Macroheterocycles through Intramolecular Oxidative Coupling of Furanoid β‐Ketoesters

“…Several other commercially available cerium(IV) complexes, as well as other known single electron oxidants, failed to surpass CAN as the reagent of choice in terms of efficiency (entries 3, 4, 7-11). It is noteworthy that the manganese(III), [9] iron(III), [10] and cobalt(II) [11] complexes shown in entries 8-11 failed to produce any of the monomeric or dimeric macrocycles.…”