<scp>Dutch Resolution</scp> of a configurationally stable [5]helquat

Severa, Lukáš; Sázelová, Petra; Cı́sařová, Ivana; Šaman, David; Koval, Dušan; Devadig, Pradeep; Kašička, Václav; Teplý, Filip

doi:10.1002/chir.22789

Cited by 3 publications

(4 citation statements)

References 70 publications

(139 reference statements)

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“…230 Note that in 2017, in the case of similar Helquats for which diastereomeric resolution with dibenzoyltartrate alone failed, a Dutch resolution using a family of three derivatives of tartrate anions was the key to achieve efficient separation of (M) and (P) helical enantiomers of configurationally stable [5]Helquat [242][OTf]. 231 This latter helicene-like compounds displayed slightly longer half-life time (see Table 20). Furthermore, a [7]Helquat was also obtained in enantiopure form via preferential crystallization of its trifluoroacetate salt, which was found to be the only conglomerate among 12 different salts studied.…”

Section: Chemical Reviewsmentioning

confidence: 99%

“…Indeed, thanks to their C 2 -symmetrical topology, a most favorable case for conglomerate occurrence, several helicene derivatives undergo spontaneous resolution. , Taking advantage of this phenomenon, Teply et al could perform a preferential crystallization experiment and obtain enantiopure samples up to 10.5 g scale of [5]Helquat salt 241 . Note that in 2017, in the case of similar Helquats for which diastereomeric resolution with dibenzoyltartrate alone failed, a Dutch resolution using a family of three derivatives of tartrate anions was the key to achieve efficient separation of ( M ) and ( P ) helical enantiomers of configurationally stable [5]Helquat [ 242 ][OTf] . This latter helicene-like compounds displayed slightly longer half-life time (see Table ).…”

Section: Helicenes Substituted With Nitrogenmentioning

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: Chemical Reviewsmentioning

confidence: 99%

Section: Helicenes Substituted With Nitrogenmentioning

confidence: 99%

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

2019

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“…Moreover, they are similar to helquats-structurally related compounds containing also two quaternary nitrogen atoms in their helical molecules. Helquat enantiomers were successfully separated by CE in the acidic sodium phosphate BGE (22 mM NaOH, 35 mM H 3 PO 4 , pH 2.5) using randomly sulfated S-α-, S-β-, and S-γ-CDs at 6 mM concentration as chiral stereoselectors [27][28][29]. For that reason, the same experimental conditions were first tested also for the enantioseparation of DQs.…”

Section: The Selection Of Experimental Conditions and The Ce Separati...mentioning

confidence: 99%

“…Among them, the native and especially the charged derivatized cyclodextrins (CDs) belong to the most often and the most successfully used chiral selectors [24][25][26]. CE using randomly sulfated α-, β-, and γ-CDs (S-α-CD, S-β-CD, and S-γ-CD, respectively) as chiral selectors was able to separate helquat enantiomers [27][28][29]. Because of the structural similarity between helquats [9] and diquats [17] (both of them being dicationic N-heteroaromatic electron-deficient molecules with axial/helical chirality and absorbing radiation in the low UV region), the aim of this work was to develop a CE method for the separation of the enantiomers of 11 DQ derivatives using the chiral selectors of the same class, that is, randomly highly sulfated α-, β-, and γ-CDs.…”

Section: Introductionmentioning

confidence: 99%

The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors

Bílek,

Koval,

Sázelová

et al. 2023

J of Separation Science

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Diquats, derivatives of the widely used herbicide diquat, represent a new class of functional organic molecules. A combination of their special electrochemical properties and axial chirality could potentially result in their important applications in supramolecular chemistry, chiral catalysis, and chiral analysis. However, prior to their practical applications, the diquats have to be prepared in enantiomerically pure forms and the enantiomeric purity of their P‐ and M‐isomers has to be checked. Hence, a chiral capillary electrophoresis (CE) method has been developed and applied for separation of P‐ and M‐enantiomers of 11 new diquats. Fast and better than baseline CE separations of enantiomers of all 11 diquats within a short time 5–7 min were achieved using acidic buffer, 22 mM NaOH, 35 mM H3PO4, pH 2.5, as a background electrolyte, and 6 mM randomly sulfated α‐, β‐, and γ‐cyclodextrins as chiral selectors. The most successful selector was sulfated γ‐cyclodextrin, which baseline separated the enantiomers of all 11 diquats, followed by sulfated β‐cyclodextrin and sulfated α‐cyclodextrin, which baseline separated enantiomers of 10 and nine diquats, respectively. Using this method, a high enantiopurity degree of the isolated P‐ and M‐enantiomers of three diquats with a defined absolute configuration was confirmed and their migration order was identified.

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Molecular structures of Ugi’s amine ferrocene-conjugates with R,R-tartaric acid and DFT calculations versus experimental resolution of their diastereomers

Borisov

Snegur

Rogatkina

et al. 2020

Journal of Molecular Structure

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Dutch Resolution of a configurationally stable [5]helquat

Cited by 3 publications

References 70 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)

The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors

Molecular structures of Ugi’s amine ferrocene-conjugates with R,R-tartaric acid and DFT calculations versus experimental resolution of their diastereomers

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