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Sayoko Nagashima, Toru Takahashi, Noor Nasrin, Satoshi Kamiguchi, Teiji Chihara, Synthesis of Chromenes by Cyclizative Condensation of Phenols with α,β-Unsaturated Carbonyl Compounds over Halide Cluster Catalysts, Chemistry Letters, Volume 45, Issue 11, November 2016, Pages 1321–1323, https://doi.org/10.1246/cl.160681
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Abstract
When phenols were reacted with α,β-unsaturated carbonyl compounds in a He stream over a silica gel-supported niobium halide cluster with an octahedral metal framework, [(Nb6Cl12)Cl2(H2O)4]·4H2O, at 200–350 °C, the catalytic activity of the cluster for cyclizative condensation developed to yield the corresponding chromenes selectively. The reaction can be seen as a substantial extension of Döbner–von Miller quinoline synthesis using phenol instead of aniline. The halide clusters of tantalum and tungsten also catalyzed the reaction.