Vanadium-Catalyzed Dehydrogenation of N-Heterocycles in Water

Abstract

In this paper, the dehydrogenation of tetrahydroquinolines using oxovanadium(V) catalysts under mild conditions in water and oxygen atmosphere is described. This catalytic technology was successfully applied to a range of other structurally related N-heterocycles, and a reaction mechanism is proposed.

Vanadium(V) Complex-Catalyzed One-Pot Synthesis of Phenanthridines via a Pictet-Spengler-Dehydrogenative Aromatization Sequence

“…At this stage in the cycle, the addition of water to C might yield tetrahydroisoquinoline 4a, which was observed by proton nuclear magnetic resonance ( 1 H NMR) analysis (vide supra), and (S)-6b. Dehydrogenative aromatization of 4a proceeds via intermediate C and a single-electron transfer from the electron-rich nitrogen center to vanadium(V) forms the intermediate D, which undergoes the dehydrogenative aromatization to give the desired product 5a [35]; when (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) (1.0 equivalent) was added to the optimal conditions, no desired product 5a was obtained at all. Under degassed N 2 instead of air, the sequential reaction proceeded to give 5a, probably due to easily auto-oxidation of 4a during analysis.…”

“…Thus, Lewis acidic vanadium(V) complex 6 would promote a Pictet-Spengler reaction of imine intermediate 3 formed by the condensation of aniline 1 and benzaldehyde 2 to afford tetrahydroisoquinoline 4. A subsequent dehydrogenative aromatization of 4, assisted by the same vanadium(V) complex, now operating as a one-electron oxidant, would yield the desired phenanthridine product 5 [28,35].…”

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

“…The present sustainable and economical approach exhibits the advantages of high catalytic potential, operational without additives, and sufficiently stability and recyclability for up to ve reuses in comparison with reported protocols. [157][158][159] Balaraman et al reported a Co-phenanthroline complex adsorbed on GO (Co-Phen@C) as a NC in the acceptorless dehydrogenation of saturated aza-heterocycles to Nheteroaromatics for the synthesis of quinoline (35a), indoles (88d), isoquinolines (39b), quinoxalines (38d), and quinazolines (42e) using potassium tert-butoxide as the base (Scheme 76). 160 They synthesized the required catalyst via the sonochemical treatment of Co(II) acetylacetonate and 1,10-phenanthroline to obtain a Co-phenanthroline complex followed by its adsorption on exfoliated GO.…”

Preparation and Uses of Chlorinated Glycerol Derivatives

“…Chlorohydrins and ECH were used to prepare derivatives of pyridine [139][140][141], phtalazines [142][143][144], oxazolidinone [122,145,146], triazinones [147], thioglycoside [148] and aziridines [149]. N-Heterocycles have wide applicability as antibiotics [150][151][152]. The evaluation of novel agents for antimicrobial activity is a very important field of study due to the emergence of bacterial resistance to classical antibiotics.…”