关键词: 4DPAIPN, 光氧化还原, 脱羧, 单氟烯烃

Herein, we report the development of 4DPAIPN based derivatives (4DPAIPN-R) as organic photocatalyst suitable for the cross-coupling of gem-difluorostyrenes with amino acids derivatives. Initially, aromatic nucleophilic substitution between 2,4,5,6-tetrafluoro-1,3-dicyanobenzene and corresponding diphenylamine have forged a series of 4DPAIPN dyes with substituents ranging from F, Cl, Br to CF₃. The basic and excited redox parameters of these dyes were investigated. The newly synthesized dye 4DPAIPN-CF₃ (E_red*=1.47 V vs. SCE) acts as an even more powerful excited oxidant than 4CzIPN (E_red*=1.35 V vs. SCE). We applied 4CzIPN, 4DPAIPN and four its derivatives (4DPAIPN-R) in the cross-coupling between gem-difluorostyrenes and amino acids derivatives. For N-phenyl glycine, we found fluoride 4DPAIPN (4DPAIPN-F) owns superior catalytic performance (25 examples). To our surprise, dyes with higher excited-state reductive potential (E_red*) proved to be ineffectual photocatalysts, for example 4CzIPN or 4DPAIPN-CF₃. For N-phenyl glycines, good catalytic performance is not linear with the oxidative potential of photocatalysts. While for N-acetyl, -Boc α-amino acids, 4DPAIPN-CF₃ possesses enough oxidative potential to promote decarboxylative and defluorative aminoalkylation of gem-difluorostyrenes (5 examples). The optimized reaction conditions were determined as follows: gem-difluorostyrenes (0.2 mmol), N-substituted amino acids (1.2 equiv.), photocatalyst (1 mol%), Cs₂CO₃ (2.0 equiv.) as the base, N,N-dimethylformamide (DMF) as the solvent, reaction at room temperature under a nitrogen atmosphere for 12 h. A mechanism investigation experiment using 2,2,6,6-tetramethyl-1-piperidi- nyloxy (TEMPO) as additive quenched the reaction, indicating the involvement of radical intermediate. The oxidative potentials of amino acid derivatives were around 0.6 V for N-phenyl glycine and around 0.9 V for N-acetyl amino-acid. The results revealed the need for different dyes depending on N-protected group of amino acids. Overall, the 4DPAIPN platform exhibits broad substrate scope, encompassing various gem-difluorostyrenes and different substituted glycine derivatives, with a total of 30 examples and yields up to 95%. The late-stage functionalization demonstrated that the resulting fluoroallylamine products could be converted into valuable fluorinated enamines and cinnamaldehyde. Lastly, further application of these photocatalysts in photoredox or energy transfer chemistry are underway.

Key words: 4DPAIPN, photo-redox, decarboxylative, mono-fluoroalkene