Synlett 2011(12): 1723-1726  
DOI: 10.1055/s-0030-1260808
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Organocatalytic Decarboxylative Doebner-Knoevenagel Reactions between Arylaldehydes and Monoethyl Malonate Mediated by a Bifunctional Polymeric Catalyst

Jinni Lu, Patrick H. Toy*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. of China
Fax: +85228571586; e-Mail: phtoy@hku.hk;
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Publikationsverlauf

Received 13 March 2011
Publikationsdatum:
29. Juni 2011 (online)

Abstract

A bifunctional polystyrene bearing both DMAP and piperidine groups has been prepared and used as an organocatalyst for decarboxylative Doebner-Knoevenagel reactions of arylaldehydes and monoethyl malonate. Isolated yields of the resulting cinnamates were very high, and in all cases only the E-isomer was detected. When a polystyrene catalyst functionalized with only DMAP or piperidine groups was used in these reactions, catalysis was much less efficient. Furthermore, catalysis using a combination of the monofunctional polymers was also less efficient than with the bifunctional polystyrene. Thus, it appears that there is a synergistic effect obtained by co-locating the two different catalytic amine groups on the same polymer backbone.

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18

See Supporting Information for details.

19

Increasing the catalyst loading did not significantly affect the isolated yield or stereoselectivity of the reaction.

20

General Procedure for Doebner-Knoevenagel Reactions
Commercially available arylaldehydes 6a-s (0.5 mmol), 7 (0.75 mmol), and catalyst 3 (0.025 mmol) were dissolved in DMF (0.5 mL). The mixture was stirred at 50 ˚C for 15-18 h, and then the reaction mixture was purified directly by column chromatography (EtOAc-hexane) to afford the desired product 8a-s. In all cases only the E-stereoisomer was observed by ¹H NMR spectroscopy.