Synthesis and some chemical transformations of (Z)- and (E)-2-acetyl-1-ferrocenyl-3-methylbuta-1,3-dienes -: A new type of cationic cycloaddition

Dehydration of (E)- and (Z)-2-acetyl-1-ferrocenyl-3-methyl-but-1-en-3-ols gave the corresponding (E)- and (Z)-2-acetyl-1-ferrocenyl-3-methylbuta-1,3-dienes, which have a cross-conjugated system of three double bonds. These heterotrienes readily afford the products of linear and cyclodimerization by following a cationic cyclodimerization mechanism; they also form Diels-Alder adducts with azodicarboxylic and maleic acid N-phenylimides. The spatial structures of (E)-2-acetyl-1-ferrocenyl-3-methylbuta-1,3-diene, (E,E)-1,5-diferrocenyl-2-isopropenyl-6-isopropylidene-3-methyl-1,3-octadiene-7-one, and 7-ferrocenyl-4-(ferrocenylmethylidene)-8-isopropylidene-1,3,5-trimethyl-9-oxabicyclo[3.3.1]non-2-ene were elucidated by X-ray diffraction analyses of single crystals. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).