Stilbenes Knoevenagel reaction

Condensations of aryiacetic acids, arylacetates and arylacetonitriles with aromatic aldehydes and ketones proceed under standard Knoevenagel conditions, providing access to stilbenes or substituted stil-benes. - Thus 3-nitrobenzaldehyde and 4-nitrophenylacetic acid react in the presence of different amines to give (130), (131) and (132). The ratio of the products varies greatly with the amine used. (131) and (132) could easily be transformed into (130) in high yield. Reaction of arylacetates with o-hydroxybenzaldehydes yields the corresponding coumarins. The condensation of 2-hydroxy-4-meth-oxybenzaldehyde (133) with pyridylacetates like (134) yields 7-methoxy-3-pyridylcoumarins like (135) (Scheme 20). 

Two triphenylamino-substituted stilbene-type chromophores, with different electron acceptors, were synthesized via Vilsmeier-Haack reaction and Knoevenagel condensation [85]. These compounds can be easily incorporated into polymer backbone... 

Various stilbene derivatives 315 have been synthesized via a tandem double Knoevenagel condensation/decarboxyl-ation/Heck reaction by Sinha et al. (Schane 13.69) [122]. This rather complex reaction seqnence is promoted by a catalyst system consisting of tetrakis(triphenylphosphine) palladium(O), piperidine, potassinm carbonate, and Uthinm chloride. It is conducted under miCTowave irradialion at 150 °C and provides the desired prodncts 315 in moderate to good yields. 

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