Pharmacologically interesting lycorines were obtained by a short, efficient method based on an intramolecular Diels-Alder reaction between an alpha-pyrone and an alkyne, followed by loss of CO(2) in a retro Diels-Alder reaction. The cyclization precursors (pyrones 9) were obtained in good yields in two or three steps from the corresponding homophthalic acid or anhydride.
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Pérez et al. (1996) studied this question.
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