A Mannich-Type Reaction in Water Employing a Dendritic Copper(II) ­Triflate Catalyst: A Positive Dendritic Effect on Chemical Yield

Abstract

A three-component Mannich-type reaction catalyzed by the Lewis acid-core metallodendrimers prepared from the dendritic 2,2′-bipyridine ligands and Cu(OTf)₂ proceeded smoothly in water. A positive dendritic effect on the chemical yields of the Mannich products was observed.

Key words

dendrimers - Lewis acids - multicomponent reaction - Mannich-type reaction - dendritic effect

References and Notes

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12

General procedure: The dendritic Lewis acid catalyst was prepared by treatment of Cu(OTf)₂ (0.03 mmol) with 1(G2[Me]) (0.03 mmol) at r.t. in dry CH₂Cl₂ (0.5 mL) for 2 h under an argon atmosphere. After removal of the solvent, the 1(G2[Me])-Cu(OTf)₂ complex was dried for 1 h in vacuo. To the 1(G2[Me])-Cu(OTf)₂ complex in H₂O (1.5 mL) was added ο-anisidine (0.33 mmol), a silyl enolate 2 (0.45 mmol) and an aldehyde (0.3 mmol). The resulting emulsion mixture was stirred for 3-16 h at r.t. (monitored by TLC). The residual oil, obtained by the usual extractive workup with CH₂Cl₂, was purified by column chromatog-raphy on silica gel to give the corresponding Mannich adducts.

13

The Mannich-type reaction also proceeded in CH₂Cl₂ by employing 1(G2[Me])-Cu(OTf)₂, but the chemical yield was low (3-phenylpropanal, ο-anisidine, silyl enolate 2b: 36% yield) because of hydrolysis of silyl enolate 2.