5-Sulfosalicylic acid catalyzed direct Mannich reaction in pure water

• A green system for metal- and surfactant-free Mannich reactions was established.
• 5-Sulfosalicylic acid is superior recyclable water-soluble organocatalyst.
• The catalytic Mannich reactions afforded β-amino ketones with excellent yields.
• The catalyst can be recycled in water whereas the product isolated by filtration.
• A new single crystal confirmed the anti-conguration of products.

A water-soluble Brønsted acid, 5-sulfosalicylic acid, efficiently catalyzed the direct three-component Mannich reactions of cyclohexanone and 3-pentanone in pure water. 21 Examples of Mannich reactions were presented, which afforded the corresponding β-amino ketones with up to 97% yield and decent diastereoselectivities. The acid catalyst can be recycled as an aqueous solution for at least six times and the yield of the Mannich product remained over 90%.

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