Tandem Electro-Oxidative C–C and C–N Coupling and Aromatization for the Construction of Pyrazine-Fused Bis-aza[7]helicene

Abstract

Repeated tandem electro-oxidative C−C and C−N coupling and aromatization were employed for the efficient construction of aza[7]helicene (BA7) as a key intermediate and the targeted pyrazine-fused bis-aza[7]helicene (PBBA7) derivatives in 90.0−93.2% isolated yields under a controlled potential. The electrosynthetic protocol showed high selectivity and enabled rapid access to functionalized organic conjugated materials from readily available polycyclic aromatic amines. A synthetic mechanistic study along with an investigation of the photoelectrical properties and application of PBBA7-C16 as a potential hole-transporting material for perovskite solar cells were performed.

Electrochemical Synthesis of Hetero[7]helicenes Containing Pyrrole and Furan Rings via an Oxidative Heterocoupling and Dehydrative Cyclization Sequence

“…In electrochemical syntheses, no oxidant is required, and oxidative transformations can be conducted under mild reaction conditions [7] . Electrosynthetic approaches of helicenes were quite rare [8a] until 2022, when Lei, Yu, and co‐workers reported a tandem electro‐oxidative protocol for the construction of pyrazine‐fused bis‐aza[7]helicene from 6‐aminochrysene in high yields [8b] . Although, the electrochemical oxidative coupling of arenols has been established, to our knowledge, no one has applied this success to get helicenes directly from arenols via a sequential electrochemical protocol [9] .…”

Recent Progress of Helicene Type Hole-Transporting Materials for Perovskite Solar Cells

“…A series of pyrazine-fused bis-aza[7]helicene (PBBA7) derivatives, synthesized by repeated tandem electro-oxidative C−C and C−N coupling and aromatization in 90.0–93.2% isolated yields, were reported by Yu et al [ 32 ]. The PBBA7-C16 was utilized as the HTM for perovskite solar cells.…”

“…Thus, it is desirable to develop alternative HTMs with low cost of production and appropriate properties capable of significantly improving the efficiency and stability of devices. Different molecular frameworks with spiro-type core [ 17 , 18 , 19 , 20 , 21 ], D-π-D [ 22 , 23 , 24 , 25 ], D-A-D [ 26 , 27 ], and helicenes [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ] have been explored to evaluate their applicability as HTMs for n-i-p PSCs.…”

Electro-organic synthesis of isatins and hydrazones through C–N cross-coupling and C(sp2)–H/C(sp3)–H functionalization

“…For this purpose, compounds 2a-p were treated with hydrazine hydrate in an undivided cell equipped with graphite carbon (2 cm 2 ) both as an anode and a cathode at room temperature (25 °C), and a constant voltage of −0.2 V was applied under ambient atmosphere for 30 min. It was found that the desired products 3a-p were formed in good to excellent yields of 75-94% in the presence of ethanol as a solvent and NaClO 4 as an electrolyte [21][22][23] as shown in Scheme 2. The data for electro-organic synthesis of hydrazone derivatives (3a-p) along with used potentials are shown in Table 2.…”