An environmentally benign synthesis of isoxazolines and isoxazoles mediated by potassium chloride in water

Synthesis of 3,5-Disubstituted Isoxazoles and Isoxazolines in Deep Eutectic Solvents

“…Therefore, there is a clear necessity for metal-free protocols. This green approach has been conducted by different oxidative reagents such as oxone, [43][44] iodine, [45][46][47] iodobenzene trifluoroacetate, 48 iodobenzene diacetate, [49][50][51] tert-butyl hypoiodite 52 or chloramine-T. 53 However, these new protocols have several inconveniencies such as stability, price and manipulation of reagents. The importance of the used solvent has been recently addressed by the use of aqueous biphasic protocols, [54][55] ionic liquid, 56 and aqueous polyethylene glycol.…”

One‐Pot Preparation of 3‐Arylisoxazole‐4,5‐dicarboxylates from Benzylic Chlorides and Acetylenedicarboxylates

“…In contrast, when p ‐chlorobenzyl p ‐tosylate ( 1a′ ) was treated with NMO, NH 2 OH · H 2 O, and then Oxone®, I , and water in the same manner, isoxazole 2a‐I was not obtained [Scheme , Equation (2)]. Thus, the chloride ion serves an important role in the oxidation of the oxime in the presence of Oxone® to give the nitrile N ‐oxide, which then undergoes a reaction with diethyl acetylenedicarboxylate ( I ) to give isoxazole 2a‐I …”

“…The aromatic aldehyde undergoes a reaction with NH 2 OH · HCl in the presence of K 2 CO 3 to form the corresponding oxime (second step). Then, the oxime is oxidized by a chloro cation, which is formed by the reaction of the chloride ion and Oxone®, to afford the nitrile N ‐oxide. The treatment of the nitrile N ‐oxide with the acetylene derivative provides the isoxazole.…”

DBU‐Mediated [3+2] Cycloaddition Reactions of Donor–Acceptor Cyclopropanes with Nitromethane: Efficient Strategy for the Construction of Isoxazole Skeletons

“…[28] These isoxazole-5-carboxylate derivatives have usually been obtained through traditional approaches, including the condensation of 1,3-dicarbonyl compounds with hydroxylamine, [29] the 1,3-dipolar cycloaddition of nitrile oxides with alkynes or their equivalents, [30] solid-phase methods that involve anchoring a nitrile oxide precursor onto resins, [31] and 1,3-dipolar cycloaddition reactions using 1,1-disubstituted bromoalkenes as alkyne equivalents for regioselective synthesis. Recently, it was reported that various oxidizers, such as Magtrieve™ (CrO 2 ), MnO 2 , [32] Oxone, [33] hydroxy(tosyloxy)iodobenzene (HTIB), [34] and tBuOI, [35] mediate the oxidation of aldoximes to nitrile oxides, and subsequent reactions with various dipolarophiles gave isoxazoles. These methods, however, suffered from several disadvantages, such as the limitation of substrates, harsh reaction conditions, and poor chemoselectivity.…”