Tandem Oxidation/Rearrangement of β-Ketoesters to Tartronic Esters with Molecular Oxygen Catalyzed by Calcium Iodide under Visible Light Irradiation with Fluorescent Lamp

Abstract

It was found that beta-ketoesters were directly transformed to the corresponding alpha-hydroxymalonic esters, tartronic esters, with molecular oxygen catalyzed by calcium iodide under visible light irradiation from fluorescent lamp. This reaction includes tandem oxidation/rearrangement and has received much attention from the viewpoint of reduction of energy consumption, labor, and solvents.

Catalytic Aerobic Photo‐oxidation of a Methyl Group on a Heterocycle to Produce an Aldehyde via Homolytic CI Bond Cleavage caused by Irradiation with Visible Light

“…We have previously described oxidation reactions using catalytic amounts of iodine and irradiation with visible light. These reactions have included the tandem oxidation and rearrangement of β‐keto esters to form α‐hydroxymalonic esters,4a the oxidative decarboxylation of 1,3‐diketones,4b and the oxidative cleavage of olefins 4c. We assumed that the homolytic cleavage and oxidation of the CI bond, promoted by irradiation with visible light, allowed the reactions to proceed.…”

Direct Synthesis of 1,2-Diketones by Catalytic Aerobic Oxidative Decarboxylation of 1,3-Diketones with Iodine and Base under Irradiation of Fluorescent Light

“…Triketone 9 and its monohydrate 10 are formed from 8, and 12 was generated by benzilic acid rearrangement in the presence of Ca(OH) 2 . 16 Hydroxycarbonate 12 is converted into 2a through oxidative decarboxylation in the presence of iodine. 17 Iodine is regenerated by aerobic photooxidation of hydrogen iodide.…”

“…Previously, we have reported aerobic photooxidation with visible light from a general-purpose fluorescent lamp. 15 Recently, we also reported the tandem oxidation-rearrangement of b-keto esters to tartronic esters in the presence of catalytic amount of CaI 2 16 and the oxidative aerobic photodecarboxylation of hydroxycarboxylic acid in the presence of catalytic amount of I 2 . 17 It occurred to us that the successive combination of oxidation, 18 rear-rangement, 19 and oxidative decarboxylation 20 will make it possible to synthesize 1,2-diketones from 1,3-diketones in one pot (Scheme 1).…”

I+/TBHP Catalysis For Tandem Oxidative Cyclization To Indolo[2,3‐b]quinolines

“…On the other hand, oxidation of 4 a with the use of I 2 proceeded to give 3 a in 67% yield (Scheme 6b, entry 3). However, no reaction was observed under dark conditions (Scheme 6b, entry 4), suggesting that a radical species (i. e., I • ) generated in situ [15] rather than I 2 itself might be the active species for the oxidation. Interestingly, the oxidation of 4 a also proceeded with the use of only TBHP (Scheme 6b, entry 5).…”

“…We could not completely rule out the possibility of a C-3-iodination pathway for N-unsubstituted indoles. On the other hand, in the radical process, [14e] abstraction of benzylic hydrogen of 4 with a freeradical species such as t-BuOO * or t-BuO * might trigger denosylative aromatization to give the indoloquinoline 1 and nosyl radical 14, which could be oxidized to the 4-nitrobenzenesulfonic acid (15). In situ protonation of free base 1 with 15 would give indoloquinoline sulfonate salts 3.…”