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Please login or sign up for a free trial to access the full content. Method 7: Heterogeneously Catalyzed and Polymer-Supported Diels–Alder Reactions

DOI: 10.1055/sos-SD-025-00268

Witulski, B.; Alayrac, C.Science of Synthesis, (200725417.

Various types of inorganic solids have been utilized to catalyze the DielsAlder reactions of enals with 1,3-dienes, such as clays,[‌52‌] zeolites,[‌53‌] or silica gel or alumina modified by Lewis acids.[‌54‌,‌55‌] Aluminum triphenoxide polymer 47 is an efficient solid catalyst for the DielsAlder reactions of enals with 1,3-dienes (Scheme 11).[‌56‌] This polymeric Lewis acid has the advantages of requiring low catalyst loadings (12mol%) and of being easily and quantitatively recoverable by filtration without loss of catalytic activity, even after several uses (up to seven times). DielsAlder reactions can also be promoted by polymer-supported catalysts. For example, polymer-bound cyclopentadienyliron(II) complex 48 mediates the cycloaddition reactions of propenal and (E)-but-2-enal with buta-1,3-dienes.[‌57‌] Catalyst 48 is easily removed by filtration and can be reused; however, this leads to some loss of activity. The preparation of 48 is based on the copolymerization of a (η5-vinylcyclopentadienyl)iron(II) complex with divinylbenzene.

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