Radical cationic domino processe

This is the only example of a radical/cationic domino process, which has been found in the literature. 

Masson and coworkers reported a-alkylation of imines through a three-component radical/cation domino process using bromomalonate 11, an enamide 13, and an alcohol as starting materials. First, an iridium species forms the alkyl radical 12 from 11 by single electron transfer (SET). Then enamide 13 reacts with 12 to produce the amidoalkyl radical 14. An oxidative radical-polar crossover reaction then furnishes an N-acyliminium cation 15, which finally reacts with nucleophilic alcohol to produce a-alkylated a-amido ether 16 (Scheme 5.5) [11]. 

Besides the numerous examples of anionic/anionic processes, anionic/pericydic domino reactions have become increasingly important and present the second largest group of anionically induced sequences. In contrast, there are only a few examples of anionic/radical, anionic/transition metal-mediated, as well as anionic/re-ductive or anionic/oxidative domino reactions. Anionic/photochemically induced and anionic/enzyme-mediated domino sequences have not been found in the literature during the past few decades. It should be noted that, as a consequence of our definition, anionic/cationic domino processes are not listed, as already stated for cationic/anionic domino processes. Thus, these reactions would require an oxidative and reductive step, respectively, which would be discussed under oxidative or reductive processes. 

For the reason of comparison and the development of new domino processes, we have created a classification of these transformations. As an obvious characteristic, we used the mechanism of the different bond-forming steps. In this classification, we differentiate between cationic, anionic, radical, pericyclic, photochemical, transition metal-catalyzed, oxidative or reductive, and enzymatic reactions. For this type... 

It can be assumed that in the domino process of, for example 5-3, a reactive radical cation intermediate 5-5 is initially formed [5]. The intramolecular cyclization then proceeds almost exclusively through a stable, chair-like, six-membered transition state 5-8 to give a distonic radical cation 5-9, which is trapped by the aromatic... 

Quite recently, Mattay and coworkers reported on several related photochemi-cally induced domino processes for the synthesis of steroids [16]. In these cases, the initially formed radical cation is stabilized by formation of an oxenium ion. For in-... 

Abstract In this chapter different types of domino-processes are described which consist of the combination of cationic, anionic, radical, pericyclic and transition metal-catalyzed as well other reactions. The methodology is used for the highly effective synthesis of carbocycles and heterocycles as well as of natural products and other interesting materials. It is also employed as an efficient tool in combinatorial chemistry. 

Domino radical reactions consisting of radical/cationic, radical/anionic, radi-cal/radical, and radical/pericyclic processes have become increasingly important... 

As was the case in our earlier publications, the total syntheses described herein were classified according to the first step of the domino process they feature. Hence, the distinction has been made between cationic, anionic, radical, pericyclic, transition-metal-catalyzed, and reductive or oxidative domino processes. 

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