Azidative Aromatization of Quinone Methides Under Transition Metal and Solvent Free Conditions

Abstract

Organic azides are synthetically and commercially useful intermediates with a wide variety of applications. In this work, azidative aromatization of quinone methides under transition metal and acid‐free conditions can avoid the forming of highly toxic and explosive hydrazoic acid and azide salts. The use of cesium carbonate as a catalyst and water as an effective additive, elimination of a transition metal catalyst, reaction solvent, and column chromatography separation led to an overall greener approach to access valuable benzyl azides in quantitative yields. Because the procedure can be used to prepare a serious of benzyl azides without contamination by any harmful transition metal residues, this new method has great potential in pharmaceutical synthesis and chemical biology studies.

Catalytic 1,1-diazidation of alkenes

“…Probably due to the steric hindrance of the multisubstituted cyclopropane structure, intermediate VII might decompose to p -quinone methide intermediate VIII via release of one molecule of nitrogen and nitrile (path A) 78 , 79 . An equilibrium might exist between VIII and diarylmethyl carbocation IX , which could be attacked by azide anion to afford diarylmethyl azide 5 80 . VII might also isomerize to intermediate X first, followed by release of nitrogen and nitrile to yield IX (path B).…”

Dibenzoylperoxide as a Versatile Oxidant for Oxidative Azidations of Phenols Using Quaternary Ammonium Iodides or Bromides.

“…We also analysed our reaction mixtures and side products to obtain further information concerning possible intermediates. p‐Quinone methides are supposed to be the most likely intermediates en route to the benzylic substitution products 2 [7,19] …”

“…p-Quinone methides are supposed to be the most likely intermediates en route to the benzylic substitution products 2. [7,19] Although we have not been able to directly detect any p-QMs, we were able to synthesize p-QM Int-I independently and successfully converted it to product 2 g under our reaction conditions. Noteworthy, the addition of NaN 3 to Int-I (in the presence of Bu 4 NI) was only possible when benzoic acid or DBPO (which forms benzoic acid in situ) were added.…”

Silylative aromatization of p-quinone methides under metal and solvent free conditions

“…Disappointed by these results, we moved attention to our previous research findings, 17 in which azidative aromatization of p -quinone methides was achieved with cesium carbonate as a catalyst and water as an effective additive under transition metal and solvent free conditions. We anticipated a solvent-free reaction condition might be a viable option so as to compensate for the lack of reactivity.…”