Intramolecular Iodine‐Mediated Oxygen Transfer from Nitro Groups to C≡C Bonds

Abstract

Highly regioselective oxygen transfer from nitro groups to C≡C bonds has been achieved by employment of iodine monochloride or molecular iodine. The precursors are heterocyclic, aromatic or acyclic compounds, each bearing a nitro group ortho to an internal alkyne. The developed methodology is general for the preparation of a wide range of fused isoxazoles, each bearing a carbonyl function in the fifth position in the isoxazole ring. It is very important to note that the outcomes of the cycloisomerizations are not dictated by the natures of the heterocycle or alkyne substituents. Moreover, this is a unique example of iodine‐mediated ring closure of internal alkynes without introduction of halogen into the newly formed rings.

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.…”

Sequential Silver‐Catalyzed Oxidative Cyclization Reactions of Unprotected 2‐Alkynylanilines to Anthranils

“…Mechanistic investigations. Anthranils 4 were obtained through the Au- [37,44] or Ir-catalyzed [45] reactions of 2-(alkylalkynyl)nitrobenzenes, the iodinemediated cycloisomerizations of nitroheterocyclic adducts, [46] Eur. J.…”

Synthesis and Facile Dearomatization of Highly Electrophilic Nitroisoxazolo[4,3-b]pyridines

“…6-R-Isoxazolo [4,3-b]pyridines 3a-j were synthesized according to a two-steps procedure, previously described in the literature for 3j [49]. Commercially available 2-chloro-3-nitropyridines 1a-e used as starting compounds were involved in Sonogashira cross-coupling with terminal alkynes In addition, these compounds are capable to undergo [4+2]-cycloadditions to the C=C(NO 2 ) aromatic bond, behaving as electron-poor dienophiles with dienes, or as heterodienes with electron-rich dienophiles within normal or inverse electronic demands, respectively [16,[33][34][35].…”

“…6-R-Isoxazolo[4,3-b]pyridines 3a-j were synthesized according to a two-steps procedure, previously described in the literature for 3j [49]. Commercially available 2-chloro-3-nitropyridines 1a-e used as starting compounds were involved in Sonogashira cross-coupling with terminal alkynes to give 2-alkynylpyridines 2a-j.…”