A facile direct synthesis of (E)-alpha-cyanocinnamaldehydes from acrylonitrile and benzaldehydes is successfully achieved in a mixed solvent of EtOH/AcOH by Pd(OAc)(2)/HPMoV/FeCl(3)/O(2) catalyst system. The reaction was found to proceed via the cross-aldol condensation of diethyl acetal derived from acrylonitrile with aldehydes.

Acetals like 3,3‐diethoxypropionate bearing electron‐withdrawing groups were found to undergo cyclodimerization and cyclotrimerization in the presence of Lewis acids to give coumalates and 1,3,5‐trisubstituted benzenes. The selectivity of these products depended on the Lewis acids employed. For instance, ethyl coumalate was obtained from ethyl 3,3‐diethoxypropionate in high selectivity under the influence of d‐block Lewis acids like FeCl3, whereas triethyl 1,3,5‐benzenetricarboxylate was obtained in preference to ethyl coumalate under the influence of lanthanoid Lewis acids like GdCl3. Various coumalates were synthesized by the FeCl3‐catalyzed cross‐cyclodimerization of acetals with active methylene compounds. From 4,4‐dimethoxy‐2‐butanone, however, 1,3,5‐triacetylbenzene, which is difficult to prepare regioselectively by conventional methods, was formed in quantitative yield under the influence of AlCl3. This reaction would provide a very convenient route to 1,3,5‐triacetylbenzene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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