Cross-conjugated Z- and E-3-ferrocenylmethyl-idene-4-methyl-2-phenylpenta-1,4-dienes — Synthesis and some chemical properties

Abstract

Dehydration of (Z)- and (E)-4-ferrocenyl-3-isopropenyl-2-phenylbut-3-en-2-ols and Z-3-ferrocenyl methyl idene-4-methyl-2-phenylpentane-2,4-diol affords (Z)- and (E)-3-ferrocenylethylidene-4-methyl-2-phenylpenta-1,4-dienes with a system of three cross-conjugated double bonds. One of the methylidene groups of the trienes obtained is smoothly protonated under the action of tetrafluoroboric acid etherate to yield (Z)- and (E)-3-ferrocenyl-2-isopropenyl-1-methyl-1-phenylallyl tetrafluoroborates. The cross-conjugated trienes undergo cationic cycloaddition to these allylic cations as well as proton-induced cyclodimerization resulting in 7-ferrocenyl-4-ferrocenylmethylidene-1,3-dimethyl-5-phenyl-8-(1-phenylethylidene)bicyclo[3.3.1]non-2-ene and isomeric 1,5-diferrocenyl-2,6-diisopropenyl-3,7-diphenylocta-1,3,6-trienes.Key words: cross-conjugated trienes, ferrocenylallylic cations, cyclodimerization, cycloaddition, ferrocene.