The scope and mechanism of a novel synthesis of 3,4-fused isoxazoles

Abstract

Thermal cyclisation of 2-nitrophenyl-and 3-nitrohetaryl-ethanoate derivatives in xylene is facilitated indirectly by 5 A molecular sieves affording an efficient general method for the construction of synthetically useful 3,4-fused isoxazoles; evidence for the mechanism of these novel heterocyclisation reactions is presented.Monocyclic isoxazoles are widely exploited1 through reductive ring scission as a valuable source of synthetically useful p-

An Unexpected Pyrimidine Ring Transformations in the Reaction of 4‐aryl‐5‐nitro‐6‐bromomethylpyrimidin‐2(1H)‐ones with Anilines

“…These compounds can be prepared either by the condensation of 4‐aminoisoxazole‐3‐carboxamides with ethyl orthoformate or through the ring contraction caused by the reduction of triazino[5,4‐d]pyrimidine 3‐oxides with stannous chloride . Heat treatment of 5‐nitropyrimidine ethanoate or iodine‐mediated ring closure of 5‐nitro‐6‐phenylethynyl‐pyrimidine affords pyrimidine‐fused isoxazoles as a result of intramolecular cyclization. At the same time, we have not encountered in the literature any references concerning the synthesis of 6,7‐dihydroisoxazolo[4,3‐d]pyrimidin‐5(4 H )‐ones.…”

Transformations of 5‐nitropyrimidines

“…Preparation of substituted isoxazolo[4,3-d]pyrimidines 79 was accomplished on the basis of nitro derivatives 75 [54] obtained via interaction of ortho-chloronitropyrimidines and malonic ester. Heating of the compound 75 resulted in elimination of an alcohol molecule and formation of ketene 76 (Scheme 31).…”

Synthesis of aromatic heterocycles

“…127 The proposed initial step is the generation of a ketene, which cyclises to the intermediate from which carbon dioxide is eliminated. 3-Aminobenzoisoxazoles have hitherto been virtually unknown but two routes to derivatives of this class, one starting with 2-fluorobenzonitriles 128 and the other from 2-fluorobenzamides, 129 have been described.…”