Aldol condensation of acyclic ketones with benzaldehyde and subsequent cyclodehydration to form indenes over halide cluster catalysts

When a molecular halide cluster [(Ta6Cl12)Cl2(H2O)4]·4H2O (1)/SiO2 was treated in a helium stream above 200 °C, it catalyzed the aldol condensation of acetone with benzaldehyde to yield E-4-phenyl-3-buten-2-one. The bromide cluster of Ta and chloride clusters of Nb, Mo, and W of the same octahedral metal framework also catalyzed the reaction. 3,3-Dimethyl-2-butanone combined with benzaldehyde similarly yielded the corresponding aldol condensation product over 1/SiO2 at 400 °C. On the other hand, 3-pentanone combined with benzaldehyde provided indenes such as E- and Z-1-ethylidene-2-methylindene and 2-methyl-3-vinylindene of the same carbon skeletal structure, which would be formed by cyclodehydration of the aldol condensation product, E-2-methyl-1-phenyl-1-penten-3-one. One of the advantages of halide cluster catalysts is thermal stability, and high temperatures above 350 °C promoted the cyclodehydration.

Graphical abstractA molecular halide cluster [(Ta6Cl12)Cl2(H2O)4]·4H2O catalyzed the aldol condensation of acetone with benzaldehyde to yield E-4-phenyl-3-buten-2-one above 200 °C. 3-Pentanone combined with benzaldehyde provided indenes such as E- and Z-1-ethylidene-2-methylindene, by cyclodehydration of the aldol condensation product, E-2-methyl-1-phenyl-1-penten-3-one. One of the advantages of halide cluster catalysts is thermal stability, and high temperatures above 350 °C promoted the cyclodehydration. Figure optionsDownload full-size imageDownload as PowerPoint slide