Redetermination of the Structure of a Water-Soluble Hypervalent Iodine(V) Reagent AIBX and Its Synthetic Utility in the Oxidation of Alcohols and Synthesis of Isoxazoline N-Oxides

Selectivity of Oxidizing Agents toward Axial and Equatorial Hydroxyl Groups

A total of 16 oxidizing reagents were screened to compare their oxidation selectivities for axial and equatorial hydroxyl moieties using steroidal methyl chenodeoxycholate, methyl deoxycholate, and 4-tert-butylcyclohexanol (cis/trans 1:1 mixture). These compounds were selected for their stable chair conformations. The results of our study demonstrated that, for the oxidation of a scaffold bearing both axial and equatorial hydroxyl groups, nitroxide-radical-based reagents should be the first choice if oxidation of the equatorial hydroxyl group is needed and Stevens or Dess-Martin reagents should be the first choice for the preferential oxidation of the axial hydroxyl group.

Five-Membered Hetarene N-Oxides: Recent Advances in Synthesis and Reactivity

Five-membered heterocyclic N-oxides attract special attention due to their significant potential applications in medicinal chemistry and advanced materials science. In this regard, novel methods for their synthesis and functionalization are in constant demand. In this short review, recent state-of-the-art achievements in the chemistry of isoxazoline N-oxides, 1,2,3-triazole 1-oxides and 1,2,5-oxadiazole 2-oxides are summarized. The main routes involving transition-metal-catalyzed and metal-free functionalization protocols along with mechanistic considerations are outlined. The transformations of these hetarene N-oxide rings as precursors to other nitrogen heterocyclic systems are also presented.

1 Introduction

2 Isoxazoline N-Oxides

3 1,2,3-Triazole 1-Oxides

4 1,2,5-Oxadiazole 2-Oxides

5 Conclusion

Singlet Oxygen Generation from a Water-Soluble Hypervalent Iodine(V) Reagent AIBX and H2O2: An Access to Artemisinin

Herein, we report an efficient method for the chemical generation of ¹O₂ by treatment of H₂O₂ with AIBX, a highly water-soluble, bench-stable, recyclable hypervalent iodine(V) reagent developed by our group. The generation of ¹O₂ was confirmed by the following results: (1) capture of ¹O₂ with the sodium salt of anthracene-9,10-bis(ethanesulfonate) produced the corresponding endoperoxide and (2) TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) produced by the oxidation of 2,2,6,6-tetramethylpiperidine with ¹O₂ generated using the AIBX/H₂O₂ system was detected by electron spin resonance spectroscopy. To illustrate the potential utility of this method for organic synthesis, we used the AIBX/H₂O₂ system to perform typical reactions of ¹O₂: [2 + 2]/[4 + 2] cycloadditions, Schenck ene reactions, and heteroatom oxidation reactions, which afforded the corresponding products in high yields. Moreover, we used the method to synthesize the antimalarial drug artemisinin. Finally, we demonstrated that AIBX could be regenerated after the reaction by means of a workup involving extraction and removal of water to obtain a precursor of AIBX, which could then be re-oxidized.

DMSO/t-BuONa/O2-Mediated Aerobic Dehydrogenation of Saturated N-Heterocycles

Aromatic N-heterocycles such as quinolines, isoquinolines, and indolines are synthesized via sodium tert-butoxide-promoted oxidative dehydrogenation of the saturated heterocycles in DMSO solution. This reaction proceeds under mild reaction conditions and has a good functional group tolerance. Mechanistic studies suggest a radical pathway involving hydrogen abstraction of dimsyl radicals from the N-H bond or α-C-H of the substrates and subsequent oxidation of the nitrogen or α-aminoalkyl radicals.