Synthesis and Some Chemical Transformations of (<i>Z</i>)‐ and (<i>E</i>)‐2‐Acetyl‐1‐ferrocenyl‐3‐methylbuta‐1,3‐dienes − A New Type of Cationic Cycloaddition

Abstract

Abstract Dehydration of ( E )‐ and ( Z )‐2‐acetyl‐1‐ferrocenyl‐3‐methylbut‐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. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)