Unlocking the Potential of Thiaheterohelicenes: Chemical Synthesis as the Key

Collins, Shawn K.; Vachon, Martin P.

doi:10.1002/chin.200643227

Cited by 4 publications

(6 citation statements)

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“…Note that helicenes including oxygen and sulfur atoms are not treated in the present review and will be published elsewhere. For related reviews see: 33,34,35,36,37,38,39 .…”

Section: Scopementioning

confidence: 99%

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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“…Note that helicenes including oxygen and sulfur atoms are not treated in the present review and will be published elsewhere. For related reviews see: 33,34,35,36,37,38,39 .…”

Section: Scopementioning

confidence: 99%

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

2019

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“…Product 2 was stored under an argon atmosphere. ), 454 (15), 378 (23), 350 (12), 281 (34), 267 (13), 253 (10), 207 (95), 183 (10). APCI HRMS: calculated for C 42 H 28 P 563.1924, found 563.1929.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Synthesis of a Helical Phosphine and a Catalytic Study of Its Palladium Complex

et al. 2020

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In this study, 9-(diphenylphosphanyl)[7]helicene was prepared as a suitable ligand for the subsequent synthesis of palladium complexes. The corresponding PdL2Cl2 complex was then successfully obtained in both racemic and enantiopure forms. The PdL2Cl2 complex emerges exclusively in the trans arrangement showing dynamic interconversion between its homo- and heterochiral forms as evidenced by 31P NMR. The trans arrangement was ultimately confirmed by X-ray crystallography using single crystals of the homochiral complex. Additionally, the PdL2Cl2 complex was subjected to screening of its catalytic activity in a Suzuki-type reaction of aryl bromides with aryl boronic acids showing fair yields of the resulting biaryls. However, the final asymmetric reactions catalyzed by the optically pure PdL2Cl2 complex provided targeted binaphtyls only in negligible enantiomeric excess.

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“…The chemistry of intrinsically chiral helicenes and their congeners has recently seen remarkable developments in terms of their synthesis and applications. [1][2][3][4] A wide variety of heterocyclic subunits can nowadays be incorporated into their helical skeletons to form azahelicenes, [5,6] thiahelicenes, [7,8] oxahelicenes, [9,10] silahelicenes, [5] borahelicenes, [5] phosphahelicenes [5] and interestingly, stable metallohelicenes. [11] Thiahelicenes have been part of helicene chemistry since the early days when Wynberg and co-workers introduced photocyclodehydrogenation of dithienylethylene-type precursors for their preparation.…”

Section: Introductionmentioning

confidence: 99%

“…This methodology allows the construction of not only parent carbohelicenes but also their N-, [10,[28][29][30][31][32][33][34] O-, [10,[35][36][37] Si- [38,39] or P-heterocyclic analogues. [40 -42] Its use for the preparation of thiahelicenes was foreseen as early as 2006 by Collins and Vachon, [7] but so far there are only two examples of the synthesis of thiahelicenes by alkyne cycloisomerization, as recently reported by Stará and Starý [27] and Guinchard, Voituriez and co-workers. [42] Herein, we report the synthesis of a series of inherently chiral (di)thiahelicenes/dithiophenohelicenes rac-1-rac-6 that contain 5, 6, 9 or 11 (hetero)cycles in their helical backbone with thiophene subunit(s) embedded in it or annulated to its periphery (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Synthesis of (Di)thiahelicenes and Dithiophenohelicenes by [2+2+2] Cycloisomerization of Alkynes

Starý

Palata

Andronova

et al. 2022

Helvetica Chimica Acta

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Dedicated to Prof. E. Peter Kündig on the occasion of his 75th birthdayA series of inherently chiral (di)thiahelicenes/dithiophenohelicenes containing 5, 6, 9 or 11 (hetero)cycles in their helical backbone with thiophene subunit(s) embedded in it or annulated to its periphery were uniformly synthesized by intramolecular alkyne [2 + 2 + 2] cycloisomerization. Their structural, chemical and physicochemical properties such as crystal packing, oxidation, barrier to racemization, spontaneous thin film transformation or electrochemical behavior were studied and compared with the respective properties of the parent all-carbon helicenes and dibenzohelicenes.

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Unlocking the Potential of Thiaheterohelicenes: Chemical Synthesis as the Key

Abstract: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Cited by 4 publications

References 1 publication

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

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

Synthesis of a Helical Phosphine and a Catalytic Study of Its Palladium Complex

Synthesis of (Di)thiahelicenes and Dithiophenohelicenes by [2+2+2] Cycloisomerization of Alkynes

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