Oxahelicene NHC ligands in the asymmetric synthesis of nonracemic helicenes

Abstract

A straightforward approach to enantiopure 2H-pyran-modified amino[5]helicenes and amino[6]helicenes was developed. They were converted to 1,3-disubstituted imidazolium salts and used as NHC ligand precursors in the Ni-catalysed enantioselective [2+2+2] cycloisomerisation of aromatic triynes to obtain the model helicene derivatives in up to 86% ee.

Synthesis and chiroptical properties of organometallic complexes of helicenic N‐heterocyclic carbenes

“…For these reasons, we have been recently investigating the development of molecular architectures associating helicenes, NHCs, and organometallic chemistry, in order to develop a new family of chiral complexes, namely, organometallic NHC‐helicene complexes (see Figure , A ‐ C ) . This strategy enabled us to create novel chiral molecular materials with unprecedented photophysical properties and potential applications in enantioselective organometallic catalysis . In this article, we present novel [4, 6]helicenic imidazolium salts ( 4a , b ) and their corresponding helicenic NHC ligands mono‐coordinated to iridium(I) ( 1a , b ) and rhodium(I) ( 1′a ) complexes.…”

Helicenes as Chirality‐Inducing Groups in Transition‐Metal Catalysis: The First Helically Chiral Olefin Metathesis Catalyst

“…[1,2] In most cases described so far,N HC-ligands have been chirally modified by introducing centers of chirality, either in the Nsubstituent or in the NHC-backbone (Figure 1). [24] This strategy has in the meantime been successfully applied to the synthesis of enantiopure aminohelicenes, [25,26] which we in turn expect to open the door to NHC ligands with helically chiral N-substituents and transitionmetal catalysts derivedt hereof. It has, for instance, been demonstrated that the reactivity of Ru-metathesis catalysts with unsaturated NHC ligands can be improved by increasing the s-donor capacity of the ligand through introduction of donor substituents in the backbone.…”

“…[19,21] Helical chirality has so far been unexplored in asymmetric transition-metalc atalysis as as tereoinformation-inducing element. [24] This strategy has in the meantime been successfully applied to the synthesis of enantiopure aminohelicenes, [25,26] which we in turn expect to open the door to NHC ligands with helically chiral N-substituents and transitionmetal catalysts derivedt hereof. [24] This strategy has in the meantime been successfully applied to the synthesis of enantiopure aminohelicenes, [25,26] which we in turn expect to open the door to NHC ligands with helically chiral N-substituents and transitionmetal catalysts derivedt hereof.…”

Synthesis of [7]Helicene Enantiomers and Exploratory Study of Their Conversion into Helically Chiral Iodoarenes and Iodanes

“…Helicenes are polycyclic molecules composed of ortho-fused aromatic rings that confer an inherently chiral helical shape to their structures. [1][2][3][4] Owing to their uniques tructural, electronic and chiroptical properties, these compounds are the focus of considerable attention in variousf ields of research, [3][4][5] notably for their potential utility in asymmetricc atalysis, [6][7][8][9][10] molecular recognition, [11][12][13][14][15] supramolecular chemistry, [16][17][18] molecular machines design, [19][20][21][22][23] liquid crystal technology, [24][25][26][27] organic (opto)electronics, [28][29][30][31][32] as well as new materials. [33][34][35][36] Several of these applications necessitate access to optically pure helicenes.…”

“…[33][34][35][36] Several of these applications necessitate access to optically pure helicenes. [2][3][4] Although af ew asymmetric synthesis approaches have relied on the use of chiral reagents or catalysts, [10,[37][38][39][40][41][42][43][44][45] most of the others were based on substrate controlt hrough the installationo fc hiral moietieso ntom olecular scaffolds prior to their annulation into helicenic systems. [46][47][48][49][50][51][52][53][54][55][56][57][58][59] However,f ully optically pure materials, which are of paramount importance for anya pplication, are rarely obtained, [45][46][47][48][49][50] and diastereoenriched mixtures generated with the help of chiral auxiliaries still need to be separated by conventional chromatography.…”