Homotropone complexes

Access to alkyl substituted derivatives of the homotropylidene complexes is provided via the >j4-tropone iron complex by reaction with diazoalkanes, followed by mild thermolysis of the 3+2 py razoline adduct to give the corresponding homotropone complexes (equation 149)217,218. The 8,8-dimethyl derivative was used as starting material for the preparation of the fluxional ( 5-2,8,8-trimethylbicyclo[5.1.0]octa-2,4-dienylium)Fe(CO)3 cation complex219. More recently (homotropone)Fe(CO)3 was used for the synthesis of unique chiral 1,2-homoheptafulvene iron complexes220 221. 

Cyclopropanation of tricarbonyl(tropone)iron 18 via cycloaddition of diazomethane, diazoethane or diazopropane and thermal dinitrogen extrusion gave bicyclo[5.1.0]octadienone ( homotropone ) complexes which decomposed to form the free ligand 20 in high yield. When the same procedure was applied to the free ligand 16, a substituted cyclooctatrienone system 17 was obtained via ring expansion. 

The absolute configuration of homotropone (150) and its Fe(CO)3 complexes was deduced from comparison between experimental and theoretically calculated (CNDO/S) CD of preferred trans conformation339. 

Synthesis of the parent homotropone 34 was achieved starting from tricarbonyl(cycloocta-tetraene)iron complex 32 via protonation and formation of the bicyclo[5.1.0]octadienylium cation complex 33. Nucleophilic addition of hydroxide and oxidation was followed by oxidative decomplexation with cerium(IV). ... 

Upon decomplexation, using various methods, cyclopropane products are obtained (see Section 5.2.6.1.1). As an example, synthesis of homotropone (9 bicyclo[5.1.0]octa-3,5-dien-2-one) is achieved starting from cyclooctatetraenetricarbonyliron complex via protonation, formation of the bicylo[5.1.0]octadienylium cation complex 8, nucleophilic addition of sodium hydroxide and oxidative decomplexation. ... 

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