Organische Elektrochemie, I: Über die elektrochemische Reduktion von 2,3‐Dioxo‐1,2,3,4‐tetra‐hydrochinoxalinen und die Autoxidation der Reduktionsprodukte

Abstract

Die elektrochemische Reduktion des I-Methyl-(2) und 1,4-Dimethyl-2,3-dioxo-1,2,3,4-tetrahydrochinoxalins (3) fiihrt im sauren Medium in einer ungewohnlichen vierelektronigen Reduktionsstufe zu I-Methyl-(4) bzw. 1,4-Dimethyl-3-oxo-l,2,3,4-tetrahydrochinoxalin (5), die unter Autoxidation jeweils die Ausgangsverbindungen zuriickbilden. Die Mechanismen der Reduktionsund Reoxidationsprozesse werden diskutiert und experimentell belegt. Es wird gezeigt, daB bei der Autoxidation die Stufe eines l-Methyl-3-oxo-3,4-dihydrochinoxalinium-Kations (15, 16) durchlaufen wird und der eingefuhrte 2-Carbonylsauerstoff aus dem Wasser stammt. Organic Electrochemistry, I Electrochemical Reduction of 2,3-Dioxo-1,2,3,4-tetrahydroquinoxalines and Autoxidation of the Reduction ProductsThe electrochemical reduction of I-methyl-(2) and 1,4-dimethyl-2,3-dioxo-1,2,3,4-tetrahydroquinoxaline (3) leads in acidic media in an unusual 4 electron reduction step to I-methyl-(4) and 1,4-dimethyl-3-oxo-l,2,3,4-tetrahydroquinoxaline (5), respectively. These compounds are converted to the starting material by autoxidation. The mechanisms of these reduction and reoxidation processes are discussed and proven experimentally. It is shown that I-methyl-3-0~0-3,4-dihydroquinoxalinium cations (15, 16) are intermediates in the autoxidation process and that the carbonyl oxygen introduced in 2-position is derived from water.

Synthesis of quinoxaline derivatives from substituted acetanilides through intramolecular quaternization reactions

“…This process has been previously observed 9 and the mechanism of oxidation of compound 72 to the corresponding quinoxaline-2,3-dione is well documented. 33 The structure of all compounds has been established on the basis of analytical and spectral data. NMR spectra of anilides deserve some comments; compounds 8, 9, 11-17, 54-57 and 61-63 give simple spectra and we assume that they appear in solution as the Z-rotamers usually found in 2Ј-substituted anilides, with strong hydrogen bonds between the NH group and the eventual heteroatoms in the ortho position.…”

“…(C-4Љ); m/z (EI) 297 (M ϩ , 36%), 260 (100), 232 (22), 218 (71), 205 (27), 192 (21), 174 (26), 164 (37), 145 (17), 131 (12), 118 (42), 105 (7) and 91 (14). (19), 205 (22), 192 (33), 177 (26), 164 (37), 145 (17), 132 (26), 118 (49), 104 (11) and 91 (15). (14), 266 (62), 251 (19), 220 (21), 164 (9), 130 (66), 117 (55), 104 (97) and 91 (32).…”

“…(31), 148 (46), 133 (100), 119 (75), 106 (11) and 92 (23). (33), 173 (99), 160 (42), 147 (36), 132 (24), 119 (89), 104 (7) and 92 (27). (24), 201 (36), 187 (100), 174 (24), 159 (30), 146 (50), 132 (49), 119 (90), 106 (11) and 92 (28).…”

“…4-Methyl-7-nitro-3,4-dihydro-1H-quinoxalin-2-one (33) (40), 160 (9), 146 (5),132 (26), 118 (12), 104 (5) and 91 (11).…”