Chemical generation of o-quinone monoimines for the rapid construction of 1,4-benzoxazine derivatives

Abstract

Highly reactive o-benzoquinone monoimines were chemically generated and successfully trapped with electron-rich olefins that led to the synthesis of hitherto unknown 1,4-benzoxazine derivatives. This unprecedented transformation was achieved by the oxidation of o-aminophenols bearing appropriate functionality on the arene residue with less expensive hypervalent iodine reagent in the presence of vinylic ethers or thioethers.

Porphyrin Cobalt(III) “Nitrene Radical” Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH)

“…However, on switching to CoP2 , the desired transformation could be achieved and product 6 was obtained in 80% yield. Non-catalytic trapping of o -quinone monoimines has been reported earlier, but the method uses stoichiometric amounts of halogen containing oxidants, which is avoided in the reaction depicted in Scheme 5 [37].…”

Hypervalent Iodine(III)‐Mediated Oxidative Dearomatizing Cyclization of Arylamines

“…Among these chemical conversions, the oxidative substitution and/or addition occurring at the nitrogen center (route a, Scheme ) using metallic and non‐metallic oxidants typically constitutes the main reaction patterns, providing a variety of synthetically useful nitrogen‐containing building blocks and precursors (e.g., hydroxylamines, nitrosoarenes, nitroarenes, nitrones, amine oxides, diazonium salts, azides, hydrazines, azoarenes, and azoxyarenes) 1,3,4. Except for the above transformations with retention of the aromaticity of the parent ring A (route a), the reactions involving the oxidative dearomatization of arylamines (route b) are also documented for the synthesis of quinoids (e.g., quinol‐imines and derivatives,5 quinone‐imine ketals,6 quinone‐imines,7d–j and quinone‐diimines7a–c,e). Compared with the vast majority of literature reports on the classical oxidation of the arylamino moiety (route a),1,3,4 however, less attention has been paid to the development of methodologies based on the selective oxidative dearomatization of arylamines, especially those involving a new carbon‐carbon bond‐forming sequence.…”

Oxidative Heterocycle Formation Using Hypervalent Iodine(III) Reagents

“…Bodipati et al [96] showed that the highly reactive o-quinone monoamine intermediates 139, generated by treatment of o-aminophenols 136 with PIDA, readily undergo completely regioselective [4 + 2] cycloadditions with vinyl ethers and phenyl vinyl sulfide to afford N-unsubstituted-1,4-benzoxazine derivatives 138 (Scheme 34).…”