香蕉视频

Radical reactions are routinely considered in synthetic planning, and highly active research continues on new ways to make and use radicals. Because the products of radical-molecule reactions are again radicals, such processes are perfectly suited to be run as sequential reactions (cascades). Likewise, because radicals can be oxidized or reduced, radical-ionic crossover reactions can be implemented. Such cascade reactions serve well the goal of step economy in organic synthesis. As compared to non-radical processes, most radical reactions are very fast. Radical chain reactions require only a small amount of an initiator and addition of a catalyst is generally not necessary. Therefore, it is often difficult to catalyze radical transformations since background chain reactions are so fast.[1]

In the lecture the concept of using the electron as a catalyst will be discussed.[1,2] It will be shown that the electron is an efficient catalyst for conducting various types of radical cascade reactions that proceed via radical and radical ion intermediates. The 鈥渆lectron is a catalyst鈥� paradigm unifies mechanistically an assortment of synthetic transformations that otherwise have little or no apparent relationship. Some recent examples on the use of the electron as a catalyst will be discussed.[3]

It will be emphasized how a negative charge can significantly weaken the neighbouring C-H bond and activate this bond towards H-atom transfer.[3e,j] Moreover, the activation of a C-H bond next to a C-radical towards deprotonation is a key point in the field of electron-catalysis. This issue will be addressed in the lecture. Extending that concept, the use of a negative charge to activate a C-C sigma-bond towards homolysis is also discussed.[3i,k] For example, electron catalyzed transition metal-free b-alkenylation-a-perfluoroalkylation of unactivated alkenes via radical 1,4 or 1,5-alkenyl migration will be presented. Electrochemistry can be applied to initiate electron-catalyzed processes.[3m]

It will be further shown, that readily generated vinyl boron ate complexes, generally used as substrates in the Suzuki-Miyaura coupling, are efficient radical acceptors to conduct electron-catalyzed modular synthesis comprising a radical polar cross over step.[3h] This approach has recently been successfully applied to the development of a novel method for the preparation of highly enantioenriched a-chiral ketones[3l] and a new method for radical borylation is discussed.[3n]

References

[1] A. Studer, D. P. Curran, Angew. Chem. Int. Ed. 2016, 55, 58-102.
[2] A. Studer, D. P. Curran, Nature Chem. 2014, 6, 765-773.
[3] (a) B. Zhang, A. Studer, Org. Lett. 2014, 16, 3990-3993. (b) D. Leifert, A Studer, Org. Lett. 2015, 17, 386-389. (c) M. Hartmann, C. G. Daniliuc, A. Studer, Chem. Commun. 2015, 51, 3121-3123. (d) D. Leifert, D. G. Artiukhin, J. Neugebauer, A. Galstyan, C. A. Strassert, A. Studer, Chem. Commun. 2016, 52, 5997-6000. (e) A. Dewanji, C. M眉ck-Lichtenfeld, A. Studer, Angew. Chem. Int. Ed. 2016, 55, 6749-6752. (f) J. Xuan, C. G. Daniliuc, A. Studer, Org. Lett. 2016, 18, 6372鈥�6375. (h) M. Kischkewitz, K. Okamoto, C. M眉ck-Lichtenfeld, A. Studer, Science 2017, 355, 936-938. (i) X. Tang, A. Studer, Chem. Sci. 2017, 8, 6888-6892. (j) T. Hokamp, A. Dewanji, M. L眉bbesmeyer, C. M眉ck-Lichtenfeld, E.-U. W眉rthwein, A. Studer, Angew. Chem. Int. Ed. 2017, 56, 13275-13278. (k) X. Tang, A. Studer, Angew. Chem. Int. Ed. 2018, 57, 814-817. (l) C. Gerleve, M. Kischkewitz, A. Studer, Angew. Chem. Int. Ed. 2018, 57, 2441-2444. (m) M. L眉bbesmeyer, D. Leifert, H. Sch盲fer, A. Studer, Chem. Commun. 2018, 54, 2240-2243. (n) Y. Cheng, C. M眉ck-Lichtenfeld, A. Studer, J. Am. Chem. Soc. 2018, 140, 6221-6225.