Base-Induced Transformation of 2-Acyl-3-alkyl-2H-azirines to Oxazoles: Involvement of Deprotonation-Initiated Pathways

Abstract

An experimental study of base-induced transformation reaction of 2-acyl-3-alkyl-2H-azirines to oxazoles indicated that a deprotonation-initiated mechanism is involved, in addition to nucleophilic addition to the imine functionality. Calculations suggested the participation of a ketenimine (ethenimine) intermediate generated by azirine ring opening of the carbanion intermediate formed by α-deprotonation of 2H-azirine. The ketenimine intermediate possessing methyl substituents at C(3) appears to be more stable than the tautomeric nitrile ylide which was proposed to be involved in photoinduced and pyrolysis reactions of 2-acyl-3-alkyl-2H-azirines to afford oxazoles. Thus, intermediacy of ketenimine is consistent with both experimental and computational results, at least under strongly basic reaction conditions.

Oxidative Cyclization of β-Aminoacrylamides Mediated by PhIO: Chemoselective Synthesis of Isoxazoles and 2H-Azirines

“…The reaction proceeded smoothly as indicated by TLC results and furnished two products, which were characterized as isomeric isoxazoles 3s and 5s on the basis of their spectral and analytical data (Scheme ). Obviously, 3s and 5s were formed through chemoselective rearrangement of 2 H -azirine 4s , , and the selectivity might be attributed to the different reactivity of O -atom in a ketone or an amide group . This finding provided an alternative protocol for the synthesis of fully substituted isoxazoles of type 3 and 5 .…”

A new highly selective “off–on” typical chemosensor of Al3+, 1-((Z)-((E)-(3,5-dichloro-2-hydroxybenzylidene)hydrazono)methyl) naphthalene-2-ol, an experimental and in silico study

“…In addition, hypsochromic shift emission maxima of 1 + Al 3+ were also observed up to 152 nm compared to the maxima of 1. Such an enhanced electronic interaction of Al 3+ with the core of 1, containing three coordination moieties, might increase planarity and stability between two aromatic parts of the chelated compound, 50 thus a blue shift was perceived significantly.…”

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

“…In the recent past, the readily accessible 2H-azirine, an efficient source of nitrogen, was employed as starting material for the synthesis of oxazole with various coupling partners such as aldehyde, trifluoroacetic acid, etc. [8,[45][46][47][48][49][50] (Scheme 1). Thiazole is a common structural motif that is found in a wide variety of naturally existing alkaloids and a number of pharmaceutically active compounds [51][52][53].…”

“…In the recent past, the readily accessible 2 H -azirine, an efficient source of nitrogen, was employed as starting material for the synthesis of oxazole with various coupling partners such as aldehyde, trifluoroacetic acid, etc. [ 8 , 45 – 50 ] ( Scheme 1 ).…”