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Towards Configurationally Stable [4]Helicenes: Enantioselective Synthesis of 12‐Substituted 7,8‐Dihydro[4]helicene Quinones
Author(s) -
Carreño M. Carmen,
Enríquez Álvaro,
GarcíaCerrada Susana,
SanzCuesta M. Jesús,
Urbano Antonio,
Maseras Feliu,
llCanals Alfons
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700762
Subject(s) - helicene , enantiopure drug , stereocenter , chemistry , enantioselective synthesis , steric effects , substituent , stereochemistry , absolute configuration , annulene , molecule , organic chemistry , catalysis
The synthesis of enantiopure C‐12 methoxy‐ or alkyl‐substituted 5,7,8,12b‐tetrahydro[4]helicene quinones 16 and 17 and the 7,8‐dihydroaromatic analogues 4 and 5 has been achieved from (S S )‐2‐( p ‐tolylsulfinyl)‐1,4‐benzoquinone. In the first series, with a structure containing both central and helical chiralities, the R absolute configuration of the stereogenic carbon atom was defined after the asymmetric cycloaddition step, whereas the P or M helicity was shown to be dependent on the nature of the C‐12 substituent. The size of this group was also defining the configurational stability of the final ( P )‐7,8‐dihydro[4]helicene quinones 4 and 5 . The interconversion barriers between the P and M helimers in the latter, computed with a DFT B3LYP method, matched well with the experimentally observed stability. Our study provided evidence that, in addition to steric effects, a small but significant role of electronic effects is governing the configurational stability of such helical quinones.