Synthesis of 2-and 2,7-Functionalized Pyrene Derivatives: An Application of Selective C-H Borylation

An efficient synthetic route to 2- and 2,7-substituted pyrenes is described. The regiospecific direct C?H borylation of pyrene with an iridium-based catalyst, prepared in situ by the reaction of [{Ir(mu-OMe)cod}2] (cod=1,5-cyclooctadiene) with 4,4'-di-tert-butyl-2,2'-bipyridine, gives 2,7-bis(Bpin)pyrene (1) and 2-(Bpin)pyrene (2, pin=OCMe2CMe2O). From 1, by simple derivatization strategies, we synthesized 2,7-bis(R)-pyrenes with R=BF3K (3), Br (4), OH (5), B(OH)2 (6), and OTf (7). Using these nominally nucleophilic and electrophilic derivatives as coupling partners in SuzukiMiyaura, Sonogashira, and BuchwaldHartwig cross-coupling reactions, we obtained 2,7-bis(R)-pyrenes with R=(4-CO2C8H17)C6H4 (8), Ph (9), C=CPh (10), C=C[{4-B(Mes)2}C6H4] (11), C=CTMS (12), C=C[(4-NMe2)C6H4] (14), C=CH (15), N(Ph)[(4-OMe)C6H4] (16), and R=OTf, R'=C=CTMS (13). Lithiation of 4, followed by reaction with CO2, yielded pyrene-2,7-dicarboxylic acid (17), whilst borylation of 2-tBu-pyrene gave 2-tBu-7-Bpin-pyrene (18) selectively. By similar routes (including Negishi cross-coupling reactions), monosubstituted 2-R-pyrenes with R=BF3K (19), Br (20), OH (21), B(OH)2 (22), [4-B(Mes)2]C6H4 (23), B(Mes)2 (24), OTf (25), C=CPh (26), C=CTMS (27), (4-CO2Me)C6H4 (28), C=CH (29), C3H6CO2Me (30), OC3H6CO2Me (31), C3H6CO2H (32), OC3H6CO2H (33), and O(CH2)12Br (34) were obtained from 2. These derivatives are of synthetic and photophysical interest because they contain donor, acceptor, and conjugated substituents. The crystal structures of compounds 4, 5, 7, 12, 18, 19, 21, 23, 26, and 2831 have also been obtained from single-crystal X-ray diffraction data, revealing a diversity of packing modes, which are described in the Supporting Information. A detailed discussion of the structures of 1 and 2, their polymorphs, solvates, and co-crystals is reported separately.