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. 2022 Feb 9;27(4):1160.
doi: 10.3390/molecules27041160.

Resolution of a Configurationally Stable Hetero[4]helicene

Michela Lupi  1 , Martina Onori  1 , Stefano Menichetti  1 , Sergio Abbate  2 , Giovanna Longhi  2 , Caterina Viglianisi  1
Affiliations

Resolution of a Configurationally Stable Hetero[4]helicene

Michela Lupi et al. Molecules. .

Abstract

We have developed an efficient chemical resolution of racemic hydroxy substituted dithia-aza[4]helicenes (DTA[4]H) 1(OH) using enantiopure acids as resolving agents. The better diastereomeric separation was achieved on esters prepared with (1S)-(-)-camphanic acid. Subsequent simple manipulations produced highly optically pure (≥ 99% enantiomeric excess) (P) and (M)-1(OH) in good yields. The role of the position where the chiral auxiliary is inserted (cape- vs. bay-zone) and the structure of the enantiopure acid used on successful resolution are discussed.

Keywords: chirality; chiroptical; enantiomers; heterohelicene; resolution; screw-shaped compounds.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
M and P enantiomers for a [6]carbohelicene.
Scheme 1
Scheme 1
Synthetic pathways (A or B) to dithia-aza[4]helicenes (DTA[4]H) 1.
Scheme 2
Scheme 2
Red-ox behavior of DTA[4]H 1.
Scheme 3
Scheme 3
Esterification with enantiopure acids 7.
Scheme 4
Scheme 4
Synthesis of hydroxy substituted helicenes 1a(OH) and 1b(OH).
Scheme 5
Scheme 5
Esterification of helicenes 1a(OH) and 1b(OH), panels (A) and (B), respectively, with enantiopure acids 7.
Figure 2
Figure 2
1H NMR spectrum of diastereomers (D1 and D2) 8bh.
Figure 3
Figure 3
1H-NMR spectra of diastereomers 8bhD1 and 8bhD2.
Scheme 6
Scheme 6
Chemical resolution of helicene (rac)-1b(OH).
Figure 4
Figure 4
Optimized 3D-structures for the two possible conformers of (M)-1b(OH). Percent population factors calculated at M06/cc-pvtz, iefpcm level; in parenthesis population factors calculated at M062X/cc-pvtz, iefpcm level.
Figure 5
Figure 5
CD (top) and absorption (bottom) experimental and calculated spectra with two choices for the DFT functional (see text); calculation performed on M-1b(OH). The calculated spectra are Boltzmann weighed averages of the two conformers A and B.
See this image and copyright information in PMC

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