The synthesis of enantiopure C-12 methoxy- or alkyl-substituted 5,7,8,12b-tetrahydrohelicene quinones 16 and 17 and the 7,8-dihydroaromatic analogues 4 and 5 has been achieved from (SS)-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-dihydrohelicene quinones 4and 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. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
|Journal||Chemistry - A European Journal|
|Publication status||Published - 22 Jan 2008|
- Asymmetric synthesis
- Helical structures