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

Abstract

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(μ‐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 Suzuki–Miyaura, Sonogashira, and Buchwald–Hartwig 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 28–31 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.