Enantiospecific Elongation of Cationic Helicenes by Electrophilic Functionalization at Terminal Ends

Romain Duwald; Simon Pascal; Johann Bosson; Stéphane Grass; Céline Besnard; Thomas Bürgi; Jérôme Lacour

doi:10.1002/chem.201703441

Enantiospecific Elongation of Cationic Helicenes by Electrophilic Functionalization at Terminal Ends

Chemistry. 2017 Oct 4;23(55):13596-13601. doi: 10.1002/chem.201703441. Epub 2017 Sep 5.

Authors

Romain Duwald¹, Simon Pascal¹, Johann Bosson¹, Stéphane Grass¹, Céline Besnard², Thomas Bürgi³, Jérôme Lacour¹

Affiliations

¹ Department of Organic Chemistry, University of Geneva, quai Ernest Ansermet 30, 1211, Geneva 4, Switzerland.
² Laboratoire de Cristallographie, University of Geneva, quai Ernest Ansermet 24, 1211, Geneva 4, Switzerland.
³ Department of Physical Chemistry, University of Geneva, quai Ernest Ansermet 30, 1211, Geneva 4, Switzerland.

PMID: 28766311
DOI: 10.1002/chem.201703441

Abstract

A strategy for late-stage electrophilic functionalizations of cationic helicenes is exposed. Thanks to strongly acidic conditions that permit reversible electrophilic substitutions, regioselective acylations, sulfonylations, or alkylations occur at the extremity(ies) of the helical cores. Extended [5] or [6]helicenes can then be generated from cationic [4]helicenes in successive one-pot elongation processes. Retention of configuration and excellent enantiospecificity (up to 99 %) are observed for the helicene growth in the enantiopure series.

Keywords: SEAr; SNAr; carbenium ions; helicenes; regioselectivity; thermodynamic control.