Enantioselective Radical Type, 1,2-Oxytrifluoromethylation of Olefins Catalyzed by Chiral Vanadyl Complexes: Importance of Noncovalent Interactions

• Published in: ACS catalysis Vol. 11; no. 12; pp. 7160 - 7175
• Main Authors: Chen, Chien-Tien, Su, Yu-Cheng, Lu, Chia-Hao, Lien, Chien-I, Hung, Shiang-Fu, Hsu, Chan-Wei, Agarwal, Rachit, Modala, Ramuasagar, Tseng, Hung-Min, Tseng, Pin-Xuan, Fujii, Ryoma, Kawashima, Kyohei, Mori, Seiji
• Format: Journal Article
• Language: English
• Published: American Chemical Society 18.06.2021
• Subjects: tandem coupling; N-hydroxyphthalimide trapping; 1,2-cross coupling; 1-aryl-2,2,2-trifluoroethanols; CF3 radical; 1-aminoxy-2,2,2-trifluoroethanes; SH2; π-π-π interaction
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.1c01813

Asymmetric three-component 1,2-oxytrifluoromethylations of styrenes were explored by using N-oxyphthalimide (NOPI) as the resulting benzylic radical anchor after cross-coupling by a CF3 radical under the catalyses of chiral N-salicylidene-derived oxovanadium­(V) complexes. Among the 15 different solvents and 15 different catalysts examined, the best scenarios were in i-PrOH with C3-tert-butyl or C3-fluoro-/2,5-dimethylphenyl-substituted vanadyl catalysts that led to the corresponding complementary S and R products in up to 88% yields and 87/86% ees, respectively, with further enrichment to at least 94% ee after a single recrystallization. The ccontrol α-(2-phenylcyclopropyl)­styrene was tested to prove the asymmetric event involving the benzylic radical species. DFT computations showed that the SOMO of the benzylic radical is placed in a way to orient the CF3CH2 group away from the tert-butyl group in the salicylidene-l-tert-butylglycinate template by interacting with the N-oxygen atom of NOPI bound to the vanadium center with a bimolecular homolytic substitution (SH2) type mechanism. The enantioselectivity profile was dominated by several noncovalent interactions between the intermediary vanadium­(NOPI) complex and the resulting benzylic radical.