Benzylic-type couplings provide an important asymmetric entry to functionalized, non-racemic helicenes

Abstract

Benzylic-type couplings are key reactions to make non-racemic helicenes.

Stereospecific Synthesis and Photophysical Properties of Propeller‐Shaped C90H48PAH

“…The enantiopure 9,10-dibromo[7]helicene was synthesized [17] from the optically pure 1,1'-bi-(2-phenanthrol) in four steps with retention of configuration and optical purity.T he latter compound can be accessed in an enantiopure form by asymmetric catalysis or with the helpo fc hiral auxiliaries. [18] To our delight, the nickel-mediated Yamamoto-type[ 2 + +2+ +2] cyclotri-merization of (M)-9,10-dibromo[7]helicene (M-2)a t1 10 8C formed exclusively diastereomer (M,M,M,P,P,P)-3 in enantiomerically pure form (Scheme 1a)i n5 7% yield.…”

Stereoselective Syntheses, Structures, and Properties of Extremely Distorted Chiral Nanographenes Embedding Hextuple Helicenes

“…Syntheses and conformational properties . It was envisioned that the chiral three‐blade propeller‐shaped hextuple helicene D 3 ‐ 2 of formula C 90 H 48 could be prepared by a Yamamoto‐type cyclotrimerization of 9,10‐dibromo[7]helicene 1 (Figure a). This new chiral PAH embeds three homochiral [7]helicene units on its outer shell and three homochiral [5]helicene units of opposite configuration on its inner edges.…”

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

“…[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. [51][52][53] Thus, the separation of helicene racemates by chiral chromatography remains today the most commonly used access to separated pairs of helicene enantiomers.…”

“…Several of these applications necessitate access to optically pure helicenes . Although a few asymmetric synthesis approaches have relied on the use of chiral reagents or catalysts, most of the others were based on substrate control through the installation of chiral moieties onto molecular scaffolds prior to their annulation into helicenic systems . However, fully optically pure materials, which are of paramount importance for any application, are rarely obtained, and diastereoenriched mixtures generated with the help of chiral auxiliaries still need to be separated by conventional chromatography .…”