Diels-Alder catalyst

Keywords stereoselective DIels-Alder reaction catalysts, DIels-Alder chiral metallocene catalyst review... 

Lewis acids as catalysts (Diels-Alder reactions),... 

Most of the synthetic approaches towards benzoannelated [2.2]paracyclo-phanes use the Diels-Alder reaction to build up the annelated rings [18,22,29]. [2.2]Paracyclophane-l-ene (32) and [2.2]paracyclophane-1,9-diene (42) can be considered as the simplest dienophiles for this purpose. Since the first syntheses of these compounds in 1958 by Cram et al. [32], various attempts have been made to get them to react with dienes in terms of Diels-Alder reactions. However, [2 + 4] cycloadditions were never observed [33], and could not be facilitated either by the application of high pressure, or the presence of Lewis acid catalysts Diels-Alder adducts were not even obtained with dienes such as tetrachloro-thiophene dioxide, known for its high reactivity in [2 + 4] cycloadditions with an inverse electron demand. All the more surprising was the observation that monoene 32 reacts smoothly with dimethyl l,2,4,5-tetrazine-3,6-dicarboxylate at room temperature leading to a dihydropyridazine-annelated paracyclophane 39 in high yield [34a]. As reported for other tetrazine Diels-Alder reactions... 

Coupling of 1,3-dienes with acrylates or acrylamides. Ru(COD)(COT) is the most efficient catalyst for this coupling to provide derivatives of 3,5-dienoic acids. In the absence of the Ru catalyst, Diels-Alder adducts are obtained,... 

The great advance in this area is the discovery that chiral organoboron dichlorides bearing a naphthalene moiety catalyze the enantioselective Diels-Alder reactions of a,p-unsaturated esters and cyclopentadiene to produce up to 99.5% ee (Scheme 23.47). A molecular complex between methyl crotononate and the catalyst was isolated. Using the same catalyst, Diels-Alder reactions between simple acyclic a,p-unsaturated ketones and a,P-unsaturated acid chlorides produce 83% and 92% ee, respectively. ... 

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