Cyclooctapyrrole mit 8er-Konformation: Enantiomerentrennung und Bestimmung der absoluten Konfiguration eines zweikernigen Metallkomplexes

A new type of [1]rotaxanes containing two aliphatic bridges between axle and wheel is obtained in 39% yield in a one-step synthesis starting from a [2]rotaxane which contained one sulfonamide group each in both the wheel and the axle. Temperature controlled chemoselective substitution reactions first at these sulfonamide nitrogens and then subsequently at the various other carboxamide nitrogens in the wheel and axle give rise to the formation of an isomeric mixture of three double-bridged [1]rotaxanes which could be separated by HPLC. Structure determination of the main product 3a was possible by NMR experiments supported by molecular modeling calculations. Using different reaction conditions, a double-substituted but not yet bridged [2]rotaxane 4 could be isolated as an intermediate giving further evidence for the assigned structure of 3a and the way of its formation. The shape of this double-bridged [1]rotaxane 3a reminds of a self-intertwining chiral "molecular 8", in which any possible racemization due to deslipping is hindered by the two stoppers originating from the former rotaxane axle. Hence, to the best of our knowledge this is the first example of a molecule in which both concepts, cycloenantiomerism and helical chirality, are realised in one structure. Enantiomer separation of the main product was possible by further HPLC using chiral stationary phases. The Cotton effects of the circular dichrograms are different to those of the already synthesized [1]rotaxanes bearing just one aliphatic bridge between axle and wheel.

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Figure-Eight Tetrathiaoctaphyrin and Dihydrotetrathiaoctaphyrin

Sprutta

Latos‐Grażyński

2001

Chem. Eur. J.

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The acid-catalyzed condensation of pyrrole and 2,5-bis(p-tolylhydroxymethyl)thiophene yields two novel giant heteroporphyrins: 5,10,15,20,25,30, 35,40-octa(p-tolyl)-41,43,45,47-tetrathia[36]octaphyrin(1.1.1.1.1.1.1.1) (S4OP) and 5,10,15,20,25,30,35,40-octa(p-tolyl)-dihydro-41,43,45,47-tetrathia[38]octaphyrin(1.1.1.1.1.1.1.1) (S4OPH2). These tetrathiaoctaphyrins are interconvertible through dihydrogenation or dehydrogenation processes. Both compounds possess helical figure-eight geometry with two thiophene rings for S4OP or two pyrrole rings for S4OPH2 in the ribbon-crossing center as shown by NOESY experiments. The synthesis of the figure-eight tetrathiaoctaphyrin implies a prearrangement process to form helical M or P dithiatetrapyrromethanes. The P-P or M-M condensation leads to the figure-eight molecule in competition with an intramolecular ring closure. Two dithiaporphyrin-like pockets of S4OP or S4OPH2 behave as independent proton acceptors. The stepwise process yields symmetric or asymmetric cationic species that depends on whether an even or odd number of NH protons are added. Dihydrotetrathiaoctaphyrin contains 38 pi electrons in its conjugation pathway, which corresponds to the formal [4n + 2] Hückel type pi-electron formulation that is consistent with a modest diatropic ring current effect in their 1H NMR spectra. The formal 4n type pi-electron formulation for tetrathiaoctaphyrin accounts for the residual paratropic shifts. A figure-eight conveyor-belt-like movement of the whole macrocyclic ring without a racemization step is proposed to account for the dynamic properties of S4OP. The molecule shuttles between two degenerate configurations. A S4OP-S4OPH2 couple may be considered as a molecular element which, while preserving the overall figure-eight geometry, "chooses" pyrrole or thiophene rings as spacers as a function of the macrocyclic oxidation state.

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Cyclooctapyrrole mit 8er-Konformation: Enantiomerentrennung und Bestimmung der absoluten Konfiguration eines zweikernigen Metallkomplexes

Cited by 49 publications

References 24 publications

Übergroße Porphyrinoide: von Molekülen mit 8er-Konformation zu nanomolekularen Hohlräumen

Übergroße Porphyrinoide: von Molekülen mit 8er-Konformation zu nanomolekularen Hohlräumen

A Self-Threaded “Molecular 8”

Figure-Eight Tetrathiaoctaphyrin and Dihydrotetrathiaoctaphyrin

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