A study into asymmetric Nicholas cyclisation reactions

Three systematic approaches have been employed to investigate asymmetric Nicholas reactions. We found that the use of a chiral N-enoyl derivative provided acceptable levels of selectivity for an intermolecular Nicholas reaction, however, we were unable to identify an auxiliary that could be utilized...

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Bibliographic Details
Published in:Tetrahedron 2007-12, Vol.63 (51), p.12769-12778
Main Authors: Tyrrell, Elizabeth, Millet, Julien, Tesfa, Kibur Hunie, Williams, Neil, Mann, Alastair, Tillett, Caroline, Muller, Christophe
Format: Article
Language:English
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Summary:Three systematic approaches have been employed to investigate asymmetric Nicholas reactions. We found that the use of a chiral N-enoyl derivative provided acceptable levels of selectivity for an intermolecular Nicholas reaction, however, we were unable to identify an auxiliary that could be utilized in an asymmetric conjugate addition and a tandem inter/intramolecular series of Nicholas reactions. The use of chiral pool non-racemic propargyl alcohols, derived from citronellal, provided enhanced levels of selectivity. As a result of these studies we developed a series of Nicholas cyclisations derived from chiral non-racemic salicylaldehyde derivatives. These underwent an extremely rapid and highly efficient cyclisation, under Nicholas conditions, to afford a range of benzopyrans. The adjacent stereogenic centres appear to be formed with high levels of stereocontrol. [Display omitted]
ISSN:0040-4020
1464-5416
DOI:10.1016/j.tet.2007.09.077