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

Abstract

A convergent synthesis of racemic 5-amino[6]hexahelicene is described. Cross-coupling reactions are used to assemble a pentacyclic framework, and a metal-catalyzed ring-closure comprises the final step. The enantiomers were separated by means of chromatography and the absolute configurations were assigned by comparison of the CD spectra with hexahelicene. The t1/2 value for racemization at 210 °C was approximately 1 hour. Scanning tunneling microscopy (STM) measurements were carried out on enantiopure and racemic samples of aminohelicene on Au(111) under ultrahigh vacuum (UHV) conditions.

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

“…301 The self-assembly of enantiopure (M) and (rac)-297 on Au(111) under UHV conditions was further investigated in 2016 (Figure 40a2). 295 The authors observed two rotational domains formed by rows of dimers oriented along the <1-11> Au crystallographic directions for the enantiopure aminohelicene being formed, according to DFT calculations, by flat-lying molecules in which the NH 2 groups govern the interaction with the surface (i.e., "N down"), whereas the C6 rings pack closely to maximize van der Waals interactions between neighboring molecules. Regarding the racemic compound, it showed the emergence of two enantiomorphous domains which are rotated by 6° with respect to the <1-11> crystallographic directions and have a double-row structure.…”

Synthesis, Properties, and Two‐Dimensional Adsorption Characteristics of [6]Hexahelicene‐7‐carboxylic acid

“…The synthesis of heptahelicene 2‐carboxylic acid has been described recently by means of cross‐coupling followed by [2+2+2] cyclization . A straightforward convergent synthesis of 5‐aminohexahelicene has recently been described by some of our group . We wished also to develop a strategy for placement of a carboxyl group in a central position on the helicene periphery using synthetic knowledge already gained from the cross‐coupling approach we had developed .…”

“…A straightforward convergent synthesis of 5‐aminohexahelicene has recently been described by some of our group . We wished also to develop a strategy for placement of a carboxyl group in a central position on the helicene periphery using synthetic knowledge already gained from the cross‐coupling approach we had developed . However, despite much effort (see the Supporting Information) a synthesis of [6]hexahelicene‐7‐carboxylic acid 1 (Figure ) based on the route of ref.…”

“…However, despite much effort (see the Supporting Information) a synthesis of [6]hexahelicene‐7‐carboxylic acid 1 (Figure ) based on the route of ref. failed.…”

“…Dehydrogenation of 11 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) was at first troublesome. When conditions analogous to a similar conversion were used (reflux in benzene) the reaction took several weeks to go to full conversion. When 1,2‐dichlorobenzene (DCB) was used at 130 °C (externally), the reaction was finished within 2 h but unidentified side products were formed.…”