Triarylborane catalysed -alkylation of amines with aryl esters

• Published in: Catalysis science & technology 2020-11, Vol.1 (22), p.7523-753
• Main Authors: Nori, Valeria, Dasgupta, Ayan, Babaahmadi, Rasool, Carlone, Armando, Ariafard, Alireza, Melen, Rebecca L
• Format: Article
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d0cy01339k

The ability of halogenated triarylboranes to accept a lone pair of electrons from donor substrates renders them excellent Lewis acids which can be exploited as a powerful tool in organic synthesis. Tris(pentafluorophenyl)borane has successfully demonstrated its ability to act as a metal-free catalyst for an ever-increasing range of organic transformations. Herein we report the N -alkylation reactions of a wide variety of amine substrates including diarylamines, N -methylphenyl amines, and carbazoles with aryl esters using catalytic amounts of B(C 6 F 5 ) 3 . This mild reaction protocol gives access to N -alkylated products (35 examples) in good to excellent yields (up to 95%). The construction of a C-N bond at the propargylic position has also been demonstrated to yield synthetically useful propargyl amines. On the other hand, unsubstituted 1 H -indoles and 1 H -pyrroles at the C3/C2 positions afforded exclusively C-C coupled products. Extensive DFT studies have been employed to understand the mechanism for this transformation. B(C 6 F 5 ) 3 is demonstrated to be an active catalyst for N -alkylation reactions of amine substrates with aryl esters.