Visible light mediated enantioselective formation of quaternary centers

The presence of chiral quaternary centers in numerous biologically active natural products highlights their importance in the field of the synthetic organic chemistry where their construction still remains a challenge. In the last years, important improvements have been achieved in the generation of quaternary stereogenic centers through the polar reactivity by carbon-carbon bond formation[1] unlike the radical transformations that have been far less successful.[2] Strategies involving both single and multiple C-C bond-forming events per chemical step have been developed for which sensitive reagents and careful temperature control are typically required. In the last years our interest has been focused in the field of difunctionalization of alkenes. The addition of CF3, N3 or P(O)Ph2 radicals to the double bond of the tosyl acrylamides triggers an one-pot cascade reaction involving trifluoromethylation, azidation or phosphonylation, aryl migration and desulfonylation affording α-aryl-β-substituted amides. In this case, the sulfone group acts as a traceless directing group.[3]
Now we have developed the enantioselective synthesis of α-aryl-β-substituted amides with a quaternary center from (SS)-N-aryl-N-(arylsulfinyl)methacrylamides by photoredox catalysis through a cascade reaction involving addition of a sulfonyl radical to the double bond, 1,5- transposition of an aryl group and elimination of the sulfoxide group. This group directs the transformation in an enantioselective manner and leaves no trace of itself by the time the cascade has come to an end.
References

[1] J. Feng, M. Holmes, M. J. Krische, Chem. Rev. 2017, 117, 12564-12580.
[2] D. Yang, S. Gu, Y.-L. Yan, H.-W. Zhao, N.-Y. Zhu, Angew. Chem. Int. Ed. 2002, 41, 3014-3017.
[3] a) W. Kong, E. Merino, C. Nevado, Angew. Chem. Int. Ed. 2014, 53, 5078-5082; b) W. Kong, M. Casimiro, E. Merino, C. Nevado, J. Am. Chem. Soc. 2013, 135, 14480-14483.