Direct Aza‐Diels–Alder Reaction in Water Catalyzed by Layered α‐Zirconium Hydrogen Phosphate and Sodium Dodecyl Sulfate

The direct aza‐Diels–Alder reaction between 2‐cyclohexen‐1‐one (1) and benzaldimines 2 in water is reported for the first time. The reaction occurs at 30 °C, is catalyzed by layered α‐zirconium hydrogen phosphate (α‐ZrP) and requires the presence of sodium dodecyl sulfate (SDS). The reaction yield is excellent, the reaction is faster and the exo diastereoselectivity is higher than when organic solvent is used. The one‐pot, three‐component version of the reaction and the recycling of both the catalyst and the aqueous mother liquor in toto (water, α‐ZrP and SDS) have also been investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)