Inverse-electron-demand Diels-Alder reactions of α,β-unsaturated hydrazones with 3-methoxycarbonyl α-pyrones.

Inverse-electron-demand Diels-Alder reactions of 3-electron-withdrawing group substituted α-pyrones with α,β-unsaturated hydrazones as electron-rich counterparts are catalyzed by Eu(hfc)3 to afford bicyclic lactone cycloadducts. This is an example of umpolung cycloaddition based on functional transformation of carbonyls to hydrazones. A subsequent dehydrazonation reaction enables indirect synthesis of carbonyl group-containing bicyclic lactones, which cannot be easily obtained by the cycloaddition of α-pyrones and enals.