Development of Palladium-Catalyzed Decarboxylative Allylation of Electron-Deficient Sulfones and Identification of Unusual Side Products
The use of sulfones as electron-withdrawing groups in substrates for palladium-catalyzed decarboxylative allylation was explored. A previously published trifluoromethanesulfonyl-based substrate was highly reactive and selective under mild conditions, but the substrate scope was not readily expanded. Instead, 3,5-bis(trifluoromethyl)phenyl sulfones were employed, thereby simultaneously retaining most of the electron deficiency and providing facile synthetic access. Optimization of the catalytic conditions to maximize the product distribution to a synthetically useful level of the allylation product over the protonation side product proved extremely challenging, with inconsistent and irreproducible results afforded with Pd 2 (dba) 3 as the palladium source. A variety of substrates were subjected to the optimized catalytic conditions of PdCp(1-cinnamyl) and Xantphos in tetrahydrofuran at 50 °C for 30 min. These conditions were applicable to all substrates with the exception of the α,α-dimethyl allyl ester, which required more forcing conditions and afforded four products: the allylation and protonation products, as expected, along with a cyclopropylation product and an unprecedented pseudodimeric product. The mechanism for the formation of these unusual side products is considered.
|Journal||Journal of Organic Chemistry|
Gill, M.A. (Monica A.), & Manthorpe, J.M. (2019). Development of Palladium-Catalyzed Decarboxylative Allylation of Electron-Deficient Sulfones and Identification of Unusual Side Products. Journal of Organic Chemistry, 84(10), 6028–6039. doi:10.1021/acs.joc.9b00068