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

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 crossconjugated 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-

Cross-conjugated 3-ferrocenylmethylidene-2,4-dimethylpenta-1,4-diene in cationic cycloaddition and proton-catalyzed cyclodimerization reactions

“…Its structure was confirmed by the data from 1 H and 13 C NMR spectra according to which the pentaene 20 is formed as a single geometrical isomer, presumably with E,E-configuration analogous to that of E,E-4-ferrocenyl-7-ferrocenylmethylidene-3-isopropylidene-6,8-dimethylnona-5,8-dien-2-one [12].…”

“…Deprotonation of the latter affords the cyclodimer 13, which is structurally similar to the cyclodimer 6 [12]. Table 1 Selected bond lengths r (Å ) and bond angles x (°) for compounds 11 and 15…”

“…Action of tetrafluoroboric acid etherate on the triene 3 afforded crystalline 1-ferrocenyl-2-isopropenyl-3,3-dimethylallilyum tetrafluoroborate (12), which is fairly stable on storage in a solid state in an inert dry atmosphere (Scheme 6).…”

“…IR (KBr), m: 819, 998, 1104, 1160, 1380, 1432, 1495, 1623, 1682, 1728 3.5. 1-Ferrocenyl-2-isopropenyl-3,3-dimethylallilyum tetrafluoroborate (12) This salt was prepared by addition of tetrafluoroboric acid etherate (0.5 ml) to a solution of the triene 3 (0.29 g, 1 mmol) in dry diethyl ether (50 ml). The crystalline black product that precipitated was filtered off, washed with dry diethyl ether and dried in vacuo.…”

“…In our previous publication [12], we reported the preparation of 3-ferrocenylmethylidene-2,4-dimethylpenta-1,4-diene (3) by dehydration of the alcohol 4 in ca. 70% yield and a new type of cationic cycloaddition of the triene 3 to the cation 5 leading to 7-ferrocenyl-4-ferrocenylmethylidene-8-isopropylidene-1,3,5-trimethyl-9-oxabicyclo-[3.3.1]non-2-ene (6) (Scheme 3).…”