From Cationic to Anionic Helicenes: New Reactivity through Umpolung

Abstract

Using a two-step reduction/metalation procedure, highly stable chiral carbenium ions are transformed into reactive carbanion intermediates. Interesting polar ketone and thioamide products are the results of this umpolung that occurs with complete retention of configuration of the helical backbone.

Synthesis and Stability of N,N′‐Dialkyl‐1,13‐dimethoxyquinacridinium (DMQA+): A [4]Helicene with Multiple Redox States

“…A forth state, the anion form of DMQA + , should also be stable had not a solvent prone to attack from strong carbanions been used. [11] A fifth redox state, a trication, could be generated irreversibly. In the case of the radical dication form of DMQA + , slow reaction kinetics alone must be responsible for the reversible electrochemistry.…”

“…The reaction occurs rapidly and can be followed by the decolouration of the solution. [11] As with the carbanion centre adducts, H-DMQA is sensitive to oxygen when in solution. As a solid, H-DMQA can be stored for years.…”

“…[11] Yet, the neutral radical state of the DMQA system has so far not been reported. Structural analogues to these carbenium ions are the neutral, nitrogen-centred [4]heterohelicenes first reported by Hellwinkel et al, [12] and Venkataraman et al later reported and studied the [5]-and [6]heterohelicenes in detail.…”

Synthesis, Properties, and Two‐Dimensional Adsorption Characteristics of 5‐Amino[6]hexahelicene

“…Further developments in the synthetic strategy and structural variation with a strong emphasis on metal‐catalyzed reactions was achieved by Stará and Starý and by Storch et al . Other interesting approaches have been developed, for example, by Miller and co‐workers and Lacour and co‐workers . This chemistry with discussion of other recent methods has been covered in four recent reviews …”

Surprisingly Difficult Resolution of N‐Methylated Cationic [4]Helicenes

“…In many instances, the compounds can be prepared in a single one-pot process and be afforded in decent to good yields (45-90%). These derivatives have been strongly studied for biological, [6][7][8] chemical, 3,9,10 photochemical/photophysical, [11][12][13][14][15][16][17][18][19][20][21] stereochemical, [22][23][24][25][26][27] structural, [28][29][30][31] supramolecular, [32][33][34] and synthetic 35,36 properties.…”