Studien zum Vorgang der Wasserstoffübertragung, 53. Beitrag zur Kenntnis der elektroreduktiven Spaltung von Hydroxylaminderivaten

Abstract

Eingegangen a m 23. Januar 1978 Die Elektroreduktion von 26 Hydroxylaminderivaten wird polarographisch und an 6 Beispielen praparativ untersucht. Es wurde gefunden: 1) Dreifach mit Alkyl-oder Arylgruppen substituierte Hydroxylaminderivate werden bis zu einem Potential von -2.5 V (gegen Ag/AgCl/KCI,,,,) nicht elektroreduziert. -2) Der Einbau von Acylgruppen erleichtert in Abhangigkeit von Art, Zahl und Verknupfungs$ielle die Elektroreduktion. Acylreste mit aromatischen Gruppen verschieben das Halbstufenpotential starker nach positiven Werten als aliphatisch substituierte Acylreste (entsprechend: Phthaloyl > Benzoyl > Formyl > Acetyl > Ethoxycarbonyl). Acylgruppen am Sauerstoff des Hydroxylamins fordern die Elektroreduktion starker als N-Acylierung. -3) Das Halbstufenpotential des durch drei Methylengruppen cyclisierte N-Benzoylhydroxylamins 5 (Funfring) liegt positiver als das Halbstufenpotential des durch vier Methylengruppen cyclisierte N-Benzoylhydroxylamin 6 (Sechsring). -4) Elektronendonatoren (OCH,) bzw. Elektronenakzeptoren (CI) im Aroylrest acylierter Hydroxylamine verschieben das Potential nach negativeren bzw, positiveren Werten. -5 ) Umwandlung des Stickstoffs in Hydroxylaminderivaten in den Oniumzustand erleichtert die elektroreduktive Spaltung. -6) Bei allen praparativ untersuchten Beispielen wird die N -0-Bindung reduzierend gespalten. Studies on the Occurrence of Hydrogen Transfer, 53'). -On the Electroreductive Cleavage of Hydroxylamine DerivativesThe electroreduction of 26 derivatives of hydroxylamine has been studied analytically (polarographically). In six cases the reaction has been carried out on a preparative scale. The results show: 1) Hydroxylamines, threefold substituted with alkyl or aryl groups, are not reduced at potentials more positive than -2.5 V (vs. Ag/AgCI/KCI,,,,). -2) The introduction of acyl groups promotes the electroreduction, the effect being dependent on the nature, site, and number of acyl functions. Aroyl groups shift to more less negative potentials than do the aliphatic counterparts, (corresponding: phthaloyl > benzoyl > formyl > acetyl > ethoxycarbonyl). 0-Acylhydroxylamines are more readily reduced than the N-acyl isomers.-3) E,,2 for Nbenzoylhydroxylamine 5, cyclized by three methylene groups (five-membered ring), is less negative than E,,, for N-benzoylhydroxylamine 6, cyclized by four methylene groups (six-membered ring). -4) Electron donors (OCH,) in the aromatic ring of the aroyl group shift El,, to more negative values, while electron acceptors (CI) have the opposite effect. -5) A full positive charge on the hydroxylamine nitrogen promotes electroreductive cleavage. -6) In all the examples investigated on a preparative scale, the N -0 bond is ruptured reductively. *) Korrespondenz bitte an diesen Autor richten.

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

“…This approach represents an alternative to oxidative decarboxylations, allowing the design of a photocatalytic cycle based on the SET reduction of the substrate. Furthermore, the relatively low reduction potential of these species (E red ≈ −1.1 V for N-acetoxyphthalimide) [44] brings them into the operational range of various organic dyes, allowing mild reaction conditions.…”

Electrochemical behavior of N‐oxyphthalimides: Cascades initiating self‐sustaining catalytic reductive N―O bond cleavage

“…The electrochemical behavior of NHPI derivatives has been scarcely studied. Only a few of cyclic voltammetric peak potentials for the electroreduction (ER) of selected O ‐acyl derivatives of NHPI in acetonitrile and the polarographic half‐wave potentials in methanol are known. One can also mention ER of benzyloxyphthalimide in aprotic medium in the presence of chlorotrimethylsilane that led to silylation of the substrate …”

Decarboxylative Cross-Electrophile Coupling of N-Hydroxyphthalimide Esters with Aryl Iodides

“… 8 Consistent with our hypothesis, nickel and zinc were required for activation of the NHP ester (entries 4 and 5), the reaction proceeded equally well in the dark (entries 1 and 2), and a less-easily reduced NHS ester did not react (entry 6). 17 …”