Iminium-Activated Aziridinations

Iminium-activated aziridinations Iminium-aetivated multicomponent reactions Iminium-activated [3-1-3] reactions... 

It is assumed that the mechanism proceeds via activation of the imine by the ruthenium catalyst (structure 169), followed by reaction with ethyl diazoacetate to generate a metal-bound ylide intermediate. Intramolecular ruthenium- assisted attack of the carbanion 170 onto the iminium ion provides the corresponding aziridine with moderate to high // selectivity. Imines bearing electron-donating groups (R2) showed significant rate enhancement. 

The vast majority of organocatalytic reactions proceeds via covalent formation of the catalyst-substrate adduct to form an activated complex. Amine-based reactions are typical examples, in which amino acids, peptides, alkaloids and synthetic nitrogen-containing molecules are used as chiral catalysts. The main body of reactions includes reactions of the so-called generalized enamine cycle and charge accelerated reactions via the formation of iminium intermediates (see Chapters 2 and 3). Also, Morita-Baylis-Hillman reactions (see Chapter 5), carbene-mediated reactions (see Chapter 9), as well as asymmetric ylide reactions including epoxidation, cyclopropanation, and aziridination (see Chapter 10), and oxidation with the in situ generation of chiral dioxirane or oxaziridine catalysts (see Chapter 12), are typical examples. 

Substrates susceptible to Sn 1 attack and those bearing leaving groups other than halides have also been employed in the Michaelis-Arbuzov reaction, for example, dialkyl sulfates, alkyl mesylates, alkyl tosylates, quaternary ammonium species, activated acetates as have other electrophiles, for example, alkyl fluoroborates, lactones, lactams, aziridines, sulfones, iminium cations, and orf/io-quinonoids.6,13-15,18... 

The indolequinone moiety is of interest (i) as the activating nucleus of aziridine alkylating substituents and/or alkylating functionality through an iminium derivative produced in a C-3 elimination process [115-118], and (ii) as a vehicle for oxygen-sensitive, bioreductively-activated drug delivery [119,120] (see below). 

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