• Corpus ID: 102611510

Atropisomerism and the synthesis of lignans

@inproceedings{Yau2001AtropisomerismAT,
  title={Atropisomerism and the synthesis of lignans},
  author={Chin Koon Yau},
  year={2001}
}

• C. Yau
• Published 1 August 2001
• Chemistry, Biology

A new synthetic methodology was developed to synthesize two chosen lignans, galbulin and cagayanin, with the intent of applying this synthetic scheme for the synthesis of stnicturally similar lignans. The Stobbe condensation was ideally suited for generating the starting materials for consûucting the aryItetralin skeleton, Two successive Stobbe condensations were executed to generate the starting dibenzylidenesuccinates. It was discovered that triflic acid-catalyzed cyclization of these dibenzylidenesuccinates produced the desired aryltetralin lignan structures in good yields. From these aryltetralin skeletons, functional interconversions were performed ultimately to generate the two target natural lignans, galbulin and cagayanin. The dibenzylidenesuccinates, upon treatment with acid, demonstrated some intriguing chemistry. in an attempt to M e r understand this cyclization step, several other dibenzylidenesuccinates with different substituent patterns were synthesized. These reactions were studied in detail to investigate the effect of the substituent patterns on the outcome of the teaction. Two plausible explanations and detailed mechanisrns were postulated to account for the formation of the aryltettalins with literature evidence to support these theones. It was also preferable that the new methodology could be utilized for the synthesis of enantiomerically pure naturaI lignans. This might be achieved by separating the dibenqlidenesuccinates into their correspondhg atropisomers. These conformational isomers, or rotamers, anse hom hindered rotation about the carbon-carbon single bond. Conventional separation proved to be diffïcuit, as the barrier to rotation about this single bond was too smaii. However, methods for coercing the dibenzylidenesuccinate to adopt one atropisomer over the other were studied and the preliminary results are presented. The intent was to force the molecule to adopt one conformation by introducing a chiral auxiliary. From this point the new synthetic methodology could be applied to the preparation of enantiomerically enriched dibenzylidenesuccinates and eventually enantiomerically e ~ c h e d natural @ms. Chapter