Isolation of Azomethine Ylides and Their Complexes: Iridium(III)‐Mediated Cyclization of Nitrone Substrates Containing Alkynes

Abstract

Dem Ruhekomplex auf der Spur: [{IrCp*Cl2}2] katalysiert die Redoxcyclisierung von Nitronalkinen wie 1 unter Bildung von Azomethinyliden, die anschließend mit Elektrophilen und π‐Bindungen umgesetzt werden können. Der ungewöhnliche O‐gebundene Azomethinkomplex 2 wurde isoliert und als Ruhezustand des Katalysators in der Azomethinylid‐Bildung identifiziert. Cp*=C5Me5.

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…Azomethine ylides can be classified as non-stabilized (where R 1 -R 5 = H or alkyl) or stabilized either by electron-withdrawing/electron-donating groups at the appropriate termini of the ylide or by N-metalation [18]. Azomethine ylides are mostly generated in situ due to their high reactivity and/or transient existence; however, in some cases, stabilized ylides have been isolated [19][20][21]. The most frequent type of 1,3-dipolar cycloaddition reaction of azomethine ylides is that with alkenyl or alkynyl dipolarophiles substituted with electron-withdrawing groups, providing access to pyrrolidine-containing molecules of biological [18,[22][23][24][25][26] or materials science interest [27][28][29][30][31].…”

Zinc‐Catalyzed Alkyne Oxidation/CH Functionalization: Highly Site‐Selective Synthesis of Versatile Isoquinolones and β‐Carbolines

“…[3,4] Recently,t he groups of Tang and Li reported that rhodium could also catalyze such an intermolecular alkyne oxidation. [5] Despite these findings, [6] synthetic application of N-oxide-mediated oxidation of alkynes faces two major technical hurdles:1)The carbene intermediate,particularly when generated from an internal alkyne such as ynamide, [7] can undergo over-oxidation which generates unwanted byproducts. [8,4c] 2) Anoble transition-metal catalyst usually is required for optimal reaction efficiency, and may severely limit the practical application of this approach because of the high cost and toxicity of the catalyst.…”

Nitrone Directing Groups in Rhodium(III)‐Catalyzed C−H Activation of Arenes: 1,3‐Dipoles versus Traceless Directing Groups

“…The formation of such bicyclics likely resulted from initial acylation of the nitrone, followed by intramolecular [3+2] dipolar addition. [13] Thus, the reaction pattern is clearly governed by the steric effects of the ortho substituent.…”