Enantioselective Synthesis of 1,12‐Disubstituted [4]Helicenes

Abstract

A highly enantioselective synthesis of 1,12‐disubstituted [4]carbohelicenes is reported. The key step for the developed synthetic route is a Au‐catalyzed intramolecular alkyne hydroarylation, which is achieved with good to excellent regio‐ and enantioselectivity by employing TADDOL‐derived (TADDOL=α,α,α,α‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol) α‐cationic phosphonites as ancillary ligands. Moreover, an appropriate design of the substrate makes the assembly of [4]helicenes of different substitution patterns possible, thus demonstrating the synthetic utility of the method. The absolute stereochemistry of the newly prepared structures was determined by X‐ray crystallography and characterization of their photophysical properties is also reported.

Enantioselective Pallada‐Electrocatalyzed C−H Activation by Transient Directing Groups: Expedient Access to Helicenes

“…Finally,w ee xplored the late-stage diversification of the thus-obtained highly enantiomerically-enriched biaryls towards chiral helicene.W hile significant advances in the synthesis of chiral helicenes have been noted, [27] asymmetric CÀHa ctivation-based electrocatalysis has thus far not been employed in the assembly of enantiopure helicenes.U pon performing ak inetic resolution on conformationally stable aldehyde 1h under the optimized reaction condition, the olefinated product 3ha was obtained with 95 % ee. Further modification provided the [5]helicene 6 with overall high chemical and optical yield (Scheme 5a).…”

α-Cationic Phosphines: from Curiosities to Powerful Ancillary Ligands

“…Along the same lines, 1,12-disubstituted [4]helicene 54 is obtained in 95% yield and 98% ee from diyne 53 employing Au complex 48h, in which the cationic moiety is a 1,3,4-[tris(mesityl)]-1,2,3-triazolium unit (Scheme 12b). 35 The Despite the successful examples just described, the modification of the cationic group attached to phosphorus not always suffices to obtain high enantioselectivities. Thus, as complementary tool to tackle additional transformations we recently introduced a new family of -cationic phosphonites 55, in which the chiral environment is provided by a BINOL skeleton.…”

Enantioselektive Pallada‐elektrokatalysierte C‐H‐Aktivierung durch transiente dirigierende Gruppen: Ein nützlicher Zugang zu Helicenen

“…Zuletzt haben wir Diversifizierungen an den hoch Enantiomeren-angereicherten Bisarylen zu Helicenen untersucht, da, trotz erheblicher erzielter Fortschritte in der Synthese chiraler Helicene, [27] die elektrokatalytische asymmetrische C-H-Aktiverung noch nicht fürd ie Darstellung enantiomerenreiner Helicene verwendet wurde.Nach einer kinetischen Racematspaltung des konformerenstabilen Aldehyd 1h unter den optimierten Reaktionsbedingungen konnte das olefinierte Produkt 3ha mit einem ee von 95 %e rhalten werden. Durch weitere Modifikationen wurde das [5]Helicen 6 mit hohen optischen und chemischen Ausbeuten dargestellt (Schema 5a)D ie Synthese von [6]Helicen 8 und [6]Helimer ent-8 wurde über den gleichen Wege rreicht.…”