Excellent acceleration of the Diels-Alder reaction by microwave irradiation for the synthesis of new fluorine-substituted ligands of NMDA receptor.

A series of 6,11-ethanobenzo[b]quinolizinium derivatives was synthesized through the Diels-Alder reaction between azoniaanthracne and the corresponding 1,1-disubstituted olefin. After a systematic investigation for achieving rapid synthesis, it was found that the reaction is accelerated in polar media such as H2O and trifluoroethanol. In particular, excellent acceleration was effected by microwave irradiation. The new fluorine-substituted ligands thus obtained exhibited potential affinity toward NMDA receptors.