Anion–π Catalysis of Diels–Alder Reactions

Abstract

Among concerted cycloadditions,t he Diels-Alder reaction is the grand old classic,which is usually achieved with acid catalysis.I nt his report, hydroxypyrones,o xa-, and thiazolones are explored because they provide access to anionic dienes.T heir [4+ +2] cycloaddition with cyclic and acyclic dienophiles,such as maleimides and fumarates,affords bicyclic products with four new stereogenic centers.B ifunctional anion-p catalysts composed of amine bases next to the p surface of naphthalenediimides (NDIs) are shown to selectively stabilizet he "open", fully accessible anionic exo transition state on the p-acidic aromatic surface.O ur results also include reactivities that are hard to access with conventional organocatalysts,s uch as the exo-specific and highly enantioselective Diels-Alder reaction of thiazolones and maleimides with complete suppression of the otherwise dominant Michael addition. With increasing p acidity of the anionp catalysts,t he rates,c hemo-, diastereo-, and enantioselectivities increase consistently.

Activation Modes in Asymmetric Anion-Binding Catalysis

“…97 98 99 Later on, the same group studied several enantioselective reactions using anion-π catalysis, 99,100 from which Diels–Alder reactions are discussed herein as selected examples. 101…”

Review on Asymmetric Catalysis Employing 5H‐Oxazol‐4‐Ones as α‐Hydroxy Carboxylic Acid Surrogates

“…Anion π‐catalysis has been found very effective in many asymmetric reactions. Matile and co‐workers have reported the first anionic [4+2] cycloaddition reaction between 5‐methyl‐ 5H ‐oxazol‐4‐ones and cyclic dienophiles (Figure 15 and Scheme 43), such as maleimides and fumarates [69] …”

“…Matile and co-workers have reported the first anionic [4 + 2] cycloaddition reaction between 5-methyl-5H-oxazol-4-ones and cyclic dienophiles (Figure 15 and Scheme 43), such as maleimides and fumarates. [69] The formation of exo adduct 116 as major was explained by the selective stabilization of fully open anionic exo transition state on the π-acidic aromatic scaffolds of the catalyst (Figure 16). The exo Diels-Alder bicyclic products bearing four stereogenic centers were obtained in quantitative yield with > 20:1 dr and 88-94% ee.…”

Anion‐π Catalysis: Focus on Nonadjacent Stereocenters

“…Moreover, by manipulating asymmetric auxiliaries, contributions from anion‐ π interactions could be expanded from chemoselectivity to stereoselectivity. These have been well exemplified by anion‐ π catalysis in asymmetric enamine and iminium chemistry, transamination, cascade processes and Diels–Alder reactions . Furthermore, biotin‐streptavidin technology provided access to the first anion‐ π enzyme .…”

“…These have been well exemplified by anion-p catalysis in asymmetric enamine [28] and iminium chemistry, [29] transamination, [30] cascade processes [31] and Diels-Alder reactions. [32] Furthermore, biotin-streptavidin technology provided access to the first anion-p enzyme. [33] Remote control of heterogeneous anion-p catalysis on electrodes by electric fields has been reported as well.…”