Catalytic Microwave-Promoted Direct Aldol Condensation Using Resin-Bound Secondary Amine

Abstract

A series of polystyrene-supported imino group-bearing catalysts were prepared. A highly efficient combination of recyclable catalysts and microwave irradiation was developed as a green protocol for the direct aldol reaction. Notably, microwaves greatly shorten the reaction times to only 20 min and improve the yield significantly. Catalyst loading was reduced as well. Different aromatic aldehydes as aldol donors were subjected to our catalyst system and afforded the corresponding products in satisfactory yields. Additionally, the polymer-supported catalysts could be recovered by simple filtration and were reusable for at least four times without significant loss of reactivity.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

GRAPHICAL ABSTRACT

Keywords:

• Aldol reaction
• imino group
• microwave
• polymer-supported reagents
• recyclability

Notes

^a Conversion based on 5, and determined by HPLC.

^b Yields were determined by HPLC.

^c In comparison to the performance without the assistance of MW irradiation.

^a Entries 1∼15–20 mol% of resin 2a.

^b entries 1∼15–10 mol% of resin 2a, MW 110 °C.

^c Conversion based on the aldehyde and determined by HPLC or GC-MS.

^d determined by HPLC or GC-MS.