Synthesis of Fluorescent 4‐Azapyrenes by Palladium(II)‐Catalyzed Dual C−H Bond Activation and Annulation

Abstract

Unique dual‐emissive and deep‐blue/green fluorescent multi‐substituted 4‐azapyrenes with bathochromic shift emission, quantum yields up to 0.60 and long excited‐state lifetime were synthesized successfully by annulative π‐extension reactions. This synthesis constitutes a palladium‐catalyzed dehydrogenative annulation of N‐acyl‐2‐aminobiaryls with in situ 1,3‐diynes as a key step, giving substituted phenanthrenes via a rollover C−H bond activation, followed by Bischler‐Napieralski cyclization. Further π‐extension by superacid‐mediated cyclization produced a blue fluorescent naphtho 4‐azapyrene.

Synthesis and Properties of 1-Azapyrenes

“…1 H NMR (250 MHz, CDCl 3 ) δ 9.28 (d, J = 5.1 Hz, 1H), 8.38 (dd, J = 8.0 Hz, J = 1.1 Hz, 1H), 8.33 (dd, J = 7.9 Hz, J = 0.9 Hz, 1H), 8.33 (s, 1H), 8.02 (s, 1H), 7.99 (d, J = 5.3 Hz, 1H), 7.98 (pt, J = 7.9 Hz, 1H), 7.77−7.49 (m, 10H). 13 (16), 368 (14), 183 (30), 176 (28), 91 (14). HRMS (EI) m/z: [M] + calcd for: C 29 H 21 N 383.1669; found 383.1669.…”

“…However, known syntheses have several limitations, and an efficient and general method applicable to the synthesis of a variety of substituted 1-azapyrenes has not been reported so far. The disadvantages of the syntheses reported to date include the need for structurally rather complex starting materials, multiple synthetic steps, and harsh reaction conditions. − Herein, we report what is, to the best of our knowledge, the first synthetic strategy for the construction of a series of substituted 1-azapyrenes. Our methodology is based on cycloisomerization of 3-aryl-2,4-bis­(arylethynyl)­pyridines mediated by Brønsted acids.…”

Synthesis and Properties of Thieno[2′,3′,4′:4,5]naphtho[1,8-cd]pyridines

“…Such a short natural lifetime and radiative decay rate, as shown by TNP-3a, is a rather common feature of pyrenes substituted at the 1-, 3-, 6-, and 8positions, where electronic coupling is most effective and the energetic order of the S 0 → S 1 ( 1 L b (α)) and S 0 → S 2 ( 1 L a (p)) transition of pyrene is strongly affected. 17,21,89,113−116 On the other hand, the natural lifetime of 2AP-Ph is comparable to those of K-region-substituted 4-azapyrenes 110 (τ 0 = 25−30 ns) and in the lower lifetime range when compared to K-regionsubstituted pyrenes 19,21,24,50,80,109 (τ 0 = 8−650 ns), 2-and 7substituted pyrenes 17,80 (τ 0 = 31−1200 ns), and pyrenes functionalized at both the K-region and 2,7-positions 24,111,112 (τ 0 = 13−226 ns). This also demonstrates the stronger perturbation of the excited states by doping with heteroatoms than it is generally induced by peripheral functionalization at these positions.…”

1,3‐Diynes: A Versatile Precursor in Transition‐Metal Catalyzed (Mediated) C−H Functionalizations

“…Interestingly, the π ‐extended nitrogen heterocycles showed dual‐emissive and deep‐blue/green colour fluorescent with narrow bandgaps and high quantum yields up to 0.60 (Scheme 40). [34] A plausible mechanism for this oxidative annulation is shown in Scheme 41. The palladium catalyst combined with N ‐acyl‐2‐aminobiaryls to activate its ortho −C−H bond to obtain intermediate‐ A .…”