One‐Step Simultaneous Synthesis of Circularly Polarized Luminescent Multiple Helicenes Using a Chrysene Framework

Abstract

A series of multiple helicenes was simultaneously synthesized in one step by intramolecular cyclization of a single chrysene derivative containing two 2-[(4-alkoxyphenyl)ethynyl]phenyl units accompanied by rearrangements of the aryl pendants. The electrophile-induced double cyclization with or without aryl migrations proceeded efficiently under acidic conditions to afford annulative p-extension of the chrysene units and produced quadruple (QH-2), triple (TH-2), and double (DH-2) helicenes containing [4]-and/or [5]helicene frameworks with dynamic and/or static helicene chirality in one step. Three multiple helicenes' structures were determined by X-ray crystallography and/or density functional theory calculations. The multiple TH-2 and DH-2 helicenes were separated into enantiomers because of the stable one and two [5]helicene moieties, respectively, and showed intense circular dichroism and circularly polarized luminescence. Although QH-2, which comprises four [4]helicene subunits, was not resolved into enantiomers, the TH-2 enantiomers were further separated into a pair of diastereomers at low temperature resulting from their substituted [4]helicene chirality. File list (2) download file view on ChemRxiv Ikai_ChemRxiv.pdf (1.17 MiB) download file view on ChemRxiv IkaiSI_ChemRxiv.pdf (23.71 MiB)

Synthesis of Single‐Handed Helical Spiro‐Conjugated Ladder Polymers through Quantitative and Chemoselective Cyclizations**

“…through an electrophile-induced intramolecular cyclization accompanied by rearrangements of the aryl pendants. [9,10] During the course of our studies, we found that the introduction of 2,6-dimethyl substituents on the 4-alkoxyphenyl pendants of the cyclization precursor, namely, (R)-1 Me (Figure 2 A), allowed the acid-promoted cyclization to proceed perfectly, without any side reactions probably due to a steric effect, thus quantitatively and chemoselectively producing (R)-2 Me as a single product, as supported by its simple 1 H NMR spectrum (Figure 2 D(iii,iv)). [11] The structure of 2 Me was unambiguously determined by single-crystal X-ray crystallography (Figure 2 C).…”

Consecutively fused single‐, double‐, and triple‐expanded helicenes

“…As a result, we, for the first time, succeeded in the perfect diastereospecific synthesis of the homochiral (all‐ P‐ or all‐ M ) consecutively fused double (ExH‐ S ) and triple (ExH‐ M ) expanded helicenes, which were exclusively produced among a number of diastereomers through quantitative and chemoselective acid‐catalyzed diastereospecific multistep cascade cyclizations of the precursors 2 and 3 even composed of a large number of complicated dynamic stereoisomers, respectively (for a multiple helicene synthesis via the gold(I)‐catalyzed cascade cyclizations with moderate to excellent diastereoselectivities, see refs 63, 69, and 70), without any side reactions, including rearrangements of aryl pendants (Figures 2c(i), (iii), (v), and S1). 54,71 The resulting chemoselectivity may arise from the steric effect of the 2,6‐dimethyl substituents on the 4‐alkoxyphenylethynyl pendants 54 . The incorporated expanded helicene subunits in the DFT‐calculated structures of ( M , M )‐ExH‐ S and ( M , M , M )‐ExH‐ M display similar helically twisted conformations with the angles between the two planes of the rings A and K ( θ AK = 28.5–32.1°) and/or those of G and Q ( θ GQ = 26.4°) (Figure 4) that are also comparable to the angle θ AK ( = 25.0 °) of ( M )‐ExH‐ C in the single crystal (Figure 3a(ii)).…”

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

“…TFA‐induced double intramolecular cyclization of chrysene derivatives 27 containing two 2‐[(4‐alkoxyphenyl)ethynyl]phenyl units gave three multiply helicenes simultaneously (quadruple [4]helicene 28 , triple helicene 29 having [4]‐ and [5]helicene frameworks and double [5]helicenes 30 ) in quantitative total yield (Scheme 5). [59] Isolated yields were not high (10, 27 and 10% for 28 a , 29 a and 30 a , respectively).…”