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

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.

1,3-bis(diarylmethylidene)-2-methylidenecyclohexanes in cycloaddition and cyclodimerization reactions. The role of stereoelectronic factors

Cycloaddition and cyclodimerization reactions of 1,3-dibenzylidene- and 1,3-bis(p-methoxybenzylidene)-2-methylidenecyclohexanes, i.e., the diaryltrienes with fixed S-cis-configurations of exocyclic double bonds are studied. These compounds undergo in situ cyclodimerization of the [4 + 2]-type upon dehydration of the precursor tertiary alcohols and form endo-adducts in the Diels-Alder reaction with N-phenylmaleimide. In the presence of CF3COOH, acid-catalyzed cyclodimerization takes place leading to methylidene-substituted spirocyclodimers, which undergo intramolecular cyclization upon prolonged contact with CF3COOH to form a fused carbocyclic system containing a central, 'three-petal' fragment of six-membered rings.

3,3-Diethyl- and 3,3-dibenzyl-1,2-diferrocenylcyclopropenes

Reactions of 2,3-diferrocenylcyclopropenone 1 with ethyl- and benzylmagnesium chlorides afford 3,3-diethyl-and 3,3-dibenzyl- 1,2-diferrocenylcyclopropenes 2 and 3, respectively, and products of nucleophilic opening of the three-membered ring resulting from the addition of RMgCl to the carbonyl group, viz., saturated ketones(4,5-diferrocenylheptan-3-ones 4a,b and 3,4-diferrocenyl-1,5-diphenylpentan-2-ones 5a,b as ca. 3: 1 mixtures of two diastereomers) and other products. The spatial structures of compounds 2 and 4a were established by X-ray diffraction analysis of single crystals. Protonation of the cyclopropenes 2 and 3 with tetrafluoroboric acid at -40 degrees C yields the corresponding 3,3-dialkyl-1 ,2-diferrocenylcyclopropylium tetrafluoroborates. Transformation of the latter into diferrocenylallylic cations upon increasing the temperature to 20 degrees C and their eprotonation under the action of N,N-dimethylaniline were studied. Electrochemical investigation of 1 and 2 shows that in both complexes the cyclopropene spacer allows electronic communication between the two outer ferrocenyl groups, this being notably greater for 2 than for 1.