Gold‐Catalyzed Enantioselective Synthesis, Crystal Structure, and Photophysical/Chiroptical Properties of Aza[10]helicenes

Tanaka, Maya; Shibata, Yu; Nakamura, Kyosuke; Teraoka, Kota; Uekusa, Hidehiro; Nakazono, Kazuko; Takata, Toshikazu; Tanaka, Ken

doi:10.1002/chem.201601622

Cited by 52 publications

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“…On the contrary, the optical rotation of 100e' (3182) was significantly larger than for 100i (1086). 134 Scheme 22. Synthesis of enantioenriched aza [6]ahelicenes 100a-e,f and bisaza [10]ahelicenes 100e' by enantioselective Au-catalyzed intramolecular hydroarylation and transformation of 100f to 100g.…”

Section: Other Cyclization Processesmentioning

confidence: 99%

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Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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In this review, we discuss the rich chemistry of helicenes and helicenoids containing maingroup elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, emission, together with other photochemical properties and applications. OUTLINE 14 The absorption spectrum of 19c recorded in CH 2 Cl 2 solutions exhibited a maximum at 376 nm which is significantly red shifted compared with that of double [5]helicene 19a (310 nm) due to the more extended π-conjugation in 19c. According to TD-DFT calculations, the low-energy absorption band from 400 to 500 nm is assignable to the HOMO→LUMO transition corresponding to a π−π* transition of the fully conjugated bis-helical system. DFT calculations revealed a very high theoretical isomerization barrier of 45.1 kcal/mol for the (P,P)/(M,M)-19c stereoisomer, i.e. 4.4 kcal/mol higher than the (P,M) stereoisomer (not observed experimentally). The high configurational stability of 19c enabled to obtain the pure (P,P)and (M,M)-19c by chiral HPLC (Daicel Chiralcel IE column; EtOAc/MeOH = 9:1 as eluent) and to study their chiroptical properties. The ECD spectrum of (P,P)-19c in CH 2 Cl 2 displayed two strong positive bands at 275 and 320 nm, a strong negative one at 375 nm and a broad and less intense one between 425-475 nm. 52 Note that the isomerization barrier of the OBO-fused double [7]helicene is much higher than for oxabora[6]helicene 9 (vide supra) and higher than carbo[7]helicene (42.0 kcal/ mol), indicating the advantage of double helicenes over monohelicenes in terms of conformational stability. Indeed no racemization was observed upon heating enantiomer (P,P) and (M,M)-19c for 24 h up to 200 °C. 52 Note that in 2017 a longer double OBO-helicene analogue was deposited on a Au(111) under UHV conditions and its surface-assisted cyclodehydrogenation into a planar OBO-perihexacene was observed by STM. 54 Similarly to 6 and 9, the strong bond alternation found in the BOC4 rings of 19a 51 may account for the small NICS value of 1.3 while the surrounding C6 rings, including the distorted central benzene ring, show large negative NICS values (Scheme 3c). For comparison, in the all-carbon analogue tetrabenzo-[a,f,j,o]perylene shown in Scheme 3c, the central C6 ring shows a positive NICS value, indicating substantial antiaromatic character. Notably, molecular orbital calculations of 19a indicate that the HOMO and LUMO are spread over the C6 rings rather than on the boron and oxygen atoms, accounting for the substantial stability of 19a (Scheme 3c). Borahelicenes are efficient blue fluorophores. Indeed, azabora[6]helicene 6 displays blue fluorescence at 447 nm (Table 2), while smaller achiral [4]helicenic systems were successfully used as host materials in phosphorescent OLEDs with efficiencies better than the classical 4,4'...

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Section: Other Cyclization Processesmentioning

confidence: 99%

“…Synthesis of S-shaped double helicene 100h and 100i. 133,134 Table 8. Specific rotation values and photophysical data of enantioenriched azahelicenes 100a-i.…”

Section: Other Cyclization Processesmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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“…Surprisingly, the synthesis of large NGs using Au-catalysis is rare but has been successfully employed for alkyne benzannulations to afford various small NGs, including chiral helicene-like compounds [104], pyrenes [71,72,84], and phenanthrenes [69,75,76].…”

Section: Acid-mediated Alkyne Benzannulationsmentioning

confidence: 99%

Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations

Senese

Chalifoux

2018

Molecules

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The extension of π-conjugation of polycyclic aromatic hydrocarbons (PAHs) via alkyne benzannulation reactions has become an increasingly utilized tool over the past few years. This short review will highlight recent work of alkyne benzannulations in the context of large nanographene as well as graphene nanoribbon synthesis along with a brief discussion of the interesting physical properties these molecules display.

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“…Therefore, their asymmetric synthesis is a highly important target in organic synthesis [3] . However, there are very few examples of the enantioselective synthesis of azahelicenes and azahelicene‐like molecules, [3a–c] in contrast to the large number of examples reported in the enantioselective synthesis of carbohelicene and carbohelicene‐like molecules [4,5] . In 2012, List achieved the enantioselective synthesis of azahelicenes including diaza[8]helicene A by the organocatalyzed annulation (Figure 1a) [3a] .…”

Section: Introductionmentioning

confidence: 99%

“…In 2012, List achieved the enantioselective synthesis of azahelicenes including diaza[8]helicene A by the organocatalyzed annulation (Figure 1a) [3a] . Subsequently, our research group reported the enantioselective synthesis of aza[6]helicenes B by the gold(I)‐catalyzed intramolecular hydroarylation of alkynes (Figure 1a) [3b,c] . The most widely used method for the enantioselective synthesis of carbohelicenes is the transition‐metal‐catalyzed [2+2+2] cycloaddition [4,6] .…”

Section: Introductionmentioning

confidence: 99%

Rhodium‐Catalyzed Enantioselective Synthesis, Structures, and Properties of Single and Double Azahelicene‐Like Molecules

Hanada

Nogami

Miyamoto

et al. 2021

Chemistry A European J

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The enantioselective synthesis of aza [6] and [7] helicene-like molecules have been achieved by the cationic rhodium(I)/axially chiral biaryl bisphosphine complex-catalyzed intramolecular [2 + 2 + 2] cycloaddition of cyanodiynes. This protocol was successfully applied to the diastereo-and enantioselective synthesis of an S-shaped double aza [6] helicene-like molecule with a high ee value of 89 %. Although no epimerization and racemization were observed in the double carbo [6]helicene-like molecule at 80°C, epimerization and racemization of the double aza[6]helicene-like molecule proceeded at 80°C. This double aza [6]helicene-like molecule showed good fluorescent quantum yields and chiroptical responses under both neutral and acidic conditions.

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Gold‐Catalyzed Enantioselective Synthesis, Crystal Structure, and Photophysical/Chiroptical Properties of Aza[10]helicenes

Cited by 52 publications

References 68 publications

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations

Rhodium‐Catalyzed Enantioselective Synthesis, Structures, and Properties of Single and Double Azahelicene‐Like Molecules

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