Domino anionic-radical process

In 2010, Maury and coworkers reported a radical/anionic domino processes initiated by ZnMe2 and air. Dimethyl zinc-mediated addition of acyloxymethyl radicals 66, formed from 65, to diethyl fumarate 67 led via the proposed intermediates 68-70 to the highly stereoselective formation of disubstituted y-lactones 71 in medium to good yields. Five equivalents of the starting iodide 65 and 3 equiv of dimethylzinc are necessary to achieve high yields (up to 98% yield). As shown in Scheme 5.16,... 

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... 

In an anionic/radical domino process an interim single-electron transfer (SET) from the intermediate of the first anionic reaction must occur. Thus, a radical is generated which can enter into subsequent reactions. Although a SET corresponds to a formal change of the oxidation state, the transformations will be treated as typical radical reactions. To date, only a few true anionic/radical domino transformations have been reported in the literature. However, some interesting examples of related one-pot procedures have been established where formation of the radical occurs after the anionic step by addition of TEMPO or Bu3SnH. A reason for the latter approach are the problems associated with the switch between anionic and radical reaction patterns, which often do not permit the presence of a radical generator until the initial anionic reaction step is finished. 

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. 

Jahn et al. reported an elegant new domino process based on the combination of anionic and radical reactions relying on a key oxidation of anion 249 followed by a radical cyclization leading to 250 (Scheme 74) [207]. Radical 250 can be trapped by TEMPO to yield functionaUzed pyrrolidine 251 in high yield and acceptable stereoselectivity the 2-3 cis relationship was controlled in the initial anionic addition, but the relative configurations at C3 and C4 were largely non-controlled. All-carbon cyclopentanes [208], in particular prostanes [209] could also be prepared through this method. More recently, Jahn and Rudakov reported its extension to nitroalkenes [210]. 

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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