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Intramolecular benzyne trapping in synthesis of a Vitamin E precursor

By Qing Xu


Intramolecular benzyne trapping by alcohols have been applied to the synthesis of a series of racemic chromans. The theme of this project was to utilise this technique in the synthesis of the precursor, (/)-8-iodo-6-methoxy-2,5,7-trimethyl chroman-2-methanol, to the natural product Vitamin E. The racemic form of the above compound has been synthesised in 12 linear steps from the commercially available 2,6-dimethyl-4-nitroanisole. Attempts to synthesize the enantiomerically enriched side chain (-)-(1S)-3,4-dihydroxy-3-methyl-1-butyne have also taken place and was achieved in seven linear steps. Methylation of 8-iodo-6-methoxy-2.5.7-trimethyl chroman-2-methanol on its 8 position was carried out by Stille coupling reaction the best result was a 25% conversion to the product. In addition, a series non-racemic chromans have also been synthesised. The benzyne precursors were prepared by condensation between the dianion 391 and allylic halides, and the chirality introduced by AD-mix reactions of the resulting alkenes

Topics: QD Chemistry
Year: 2004
OAI identifier: oai:
Provided by: ORCA
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