DBU-Induced Phenol-Keto Resonance in 3,5-Dihydroxyphthalide: Regioselectivities in Condensations with α,β-Unsaturated Aldehydes - Facile Synthesis of Bioactive Natural and Unnatural Benzopyrans [1]

Abstract

Remarkably tuned regioselectivities are obtained in the condensation of 3,5-dihydroxyphthalide (1) with several α,β-unsaturated aldehydes using DBU and neutral conditions. The linear (65-81%) and angular (51-60%) bioactive natural and unnatural ­benzopyran derivatives are produced exclusively in one step and are described via phenol-keto resonance.

Key words

3,5-dihydroxyphthalide - phenol-keto resonance - regio­selective condensation - α,β-unsaturated aldehydes - benzopyran synthesis

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NCL Communication No. 6659.

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NCL Communication No. 6659.

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Upon silica gel column chromatographic purification of 3, only 1 was eluted from the column. Neutral alumina column purification gave only DBU.