Asymmetric Intramolecular Diels-Alder Cycloadditions of 2-Pyrone-3-Carboxylates and Synthesis of Vitamin D3 a Ring Phosphine Oxide

Cheon-Gyu Cho, Gary H. Posner

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Abstract

Intramolecular Diels-Alder cycloadditions of 2-pyrone-3-carboxylates with trans-vinyl silaketal groups tethered via a chiral, non-racemic 1,3-butanediol auxiliary proceeded in unexpected stepwise cycloadditions through ionic intermediates to provide cis-disubstituted bicylolactones. The ratio of two isomers, exo and endo, was 5 to 1, and each isomer was found to be diastereomerically pure (>99% de). Their relative and absolute stereochemistries were determined by 1H NMR spectroscopy and confirmed by X-ray crystallography of minor, endo-adduct 9. The major exo-adduct was successfully transformed to (-)-2-butyl substituted A-ring phophine oxide 16, a key element for the synthesis of 2-butyl vitamin D3.

Original languageEnglish
Pages (from-to)957-961
Number of pages5
JournalBulletin of the Korean Chemical Society
Volume19
Issue number9
Publication statusPublished - 1998 Sep 20

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