Microwave versus Conventional Light Activation of O‐Radical Scission Processes

Abstract

Domino or sequential processes initiated by cleavage of O radicals has led to the conversion of low‐cost, readily available substrates into high‐profit products. The optimization of these processes by using different activation sources (irradiation with visible light, microwaves, and conventional heating) is described herein, as well as their application to the conversion of carbohydrates, amino acids, peptides, and terpenes into valuable derivatives.

Synthesis, Biological Evaluation, and Molecular Docking Study of 3-Amino and 3-Hydroxy-seco A Derivatives of α-Amyrin and 3-Epilupeol as Inhibitors of COX-2 Activity and NF-kB Activation

“…Some strategies have been employed to obtain seco-triterpenes, including Beckmann fragmentation, 23,24,27,35 Schmidt reaction, 19 application of the taraxerane−oleanane rearrangement, 36 nucleophilic formylation and cyanation of conjugated enones, 30 and Baeyer−Villiger oxidation of the C-3 ketone. 22,25,26,28 Considering the importance of developing novel antiinflammatory agents, we explored the chemical modification in ring A of the anti-inflammatory natural triterpenes α-amyrin (1) and 3-epilupeol (2) by using the one-pot radical scission− oxidation process developed by Boto et al 37,38 So, treatment of α-amyrin 1 with (diacetoxyiodo)benzene (PhI(OAc) 2 ) and iodine (I 2 ) under irradiation with visible light at 26 °C afforded a separable mixture of 1a and 1b in 38% and 4% yield, respectively. The compounds 1a and 1b resulting from the scission− oxidation process are valuable precursors to other compounds by the transformation of the aldehyde group.…”

“Doubly Customizable” Unit for the Generation of Structural Diversity: From Pure Enantiomeric Amines to Peptide Derivatives

“…Thus, commercial hydroxyproline derivative 7 was transformed into benzyl ether 8 and bulky silyl ether 9 in good yields . These substrates underwent radical decarboxylation–oxidation by treatment with (diacetoxyiodo)­benzene (DIB) and iodine under irradiation with visible light, generating a 2-acetoxypyrrolidine (not shown) . This intermediate was treated in situ with a Lewis acid to generate an iminium ion ( 8a or 9a ), which was trapped by C-nucleophiles. , In the case of small nucleophile allyltrimethylsilane (allylTMS), both substrates were transformed into 2,4-cis products 10 and 11 .…”

“…These substrates underwent radical decarboxylation–oxidation by treatment with (diacetoxyiodo)­benzene (DIB) and iodine under irradiation with visible light, generating a 2-acetoxypyrrolidine (not shown) . This intermediate was treated in situ with a Lewis acid to generate an iminium ion ( 8a or 9a ), which was trapped by C-nucleophiles. , In the case of small nucleophile allyltrimethylsilane (allylTMS), both substrates were transformed into 2,4-cis products 10 and 11 . The prevalence of the cis product over the less hindered trans isomer is due to a stereoelectronic effect described by Woerpel for 4-substituted five-membered cyclic iminium ions. , Thus, when the substituent at C-4 is an oxygenated function, the iminium intermediate 8a or 9a adopts an envelop conformation, where axial H-groups hinder the introduction of nucleophiles from the face opposite to the OP group.…”

“Cut and Paste” Processes in the Search of Bioactive Products: One-Pot, Metal-free O-Radical Scission-Oxidation-Addition of C, N or P-Nucleophiles

“…Our group and others have described different applications of the β-scission of O -radicals, generated from alcohols, acetals or acids under Suárez conditions, to the preparation of bioactive products or their analogs ( Saavedra et al, 2020 ; Cuevas et al, 2021 and references cited therein). However, in these protocols a further development was introduced: coupling these oxidative scission processes to the addition of carbon, nitrogen, phosphorous, oxygen, hydrogen, sulfur and other nucleophiles ( Boto, Gallardo et al, 2006 ; 2007a ; Boto, Hernández et al, 2008a,b ; 2009 ; Batchu et al, 2014 ; Carro et al, 2017 ; Saavedra et al, 2018 ; Santana and González, 2020 ). In effect, the scission generates a C -radical that can be readily oxidized to a cationic intermediate when the latter is stabilized by adjacent groups.…”