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