4,5-Homotropones

Dialkylated 4-cycloheptenones such as (58) are utilized as key intermediates in the preparation of various kinds of troponoid compounds, including 2,7-dialkylated tropones (97), y-tiopolones (98) and 4,5-homotropones (99), 9 -60= which exist as hydrohomotropylium ions (100) in concentrated sulfuric acid. ... 

Tropone itself gives with diazomethane a 3 1 mixture of 1- and 2-methylcycloheptapyrazol-4-ones (143a,b), along with cyclooctatrienone and 2,3-homotropone (72TL1925). Here the regiochemistry of cycloaddition is the reverse of that of diazomethane with simple a,/3-unsaturated carbonyl compounds (80MI1, p.282). The different behavior of tropone and, e.g.. 

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. 

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. 

Cycloaddition is the major mode of photoreaction between ethylenes and naphthalenes, and the product (58) from (3-naphthol and acrylonitrile has been photo-oxidized in benzene solution in the presence of mercuric oxide and iodine to give (59) in 40% yield." Formation of (59) involves a novel rearrangement and provides a convenient two-step entry into homotropones. 

Examples of the generation and use of oxyl radicals, obtained by photolysis of hypoiodites, have again been described. The conversion of 7-cyano-2,3-benzobicyclo[4.2.0]octa-2,4-dien-6-ol (204) into the homotropone (205) on irradiation in benzene in the presence of HgO-l2 can be rationalized in this way a possible explanation is shown in Scheme 8. 

Suginome et al. have described a novel route to homotropones which involves the unprecedented oxidative rearrangement (18) — (19). The photoaddition of tetramethylethylene to the azaphenanthrene (20), giving (21), is likewise wholly unexpected and without precedent (Oberti et al.). 

When 3,3-dimethylcyclopropene is exposed to carbon monoxide under pressure in the presence of tetrakis(triphenylphosphane)palladium as catalyst, 3,3,6,6,10,10-hexamethyl-exo,enrfo-tet-racyclo[7.1.0.0 " .0 ]decan-8-one (hexamethyl-tris-cr-homotropone, 10) is formed as the main product (72.2%) along with carbonyl-free di- and oligomerization products. At ambient pressure with an in situ generated palladium(O) catalyst, only a 20% yield of the tetracyclic ketone 10 is obtained. 

Dichlorobis(triphenylphosphane)palladium as catalyst leads to mixtures of the tetracyclic homo-cyclotrimer 11 and the tris-cr-homotropone 12 with both 3,3-dimethyl- and 3,3-diphenyl-cyclopropene in relatively low yields. ... 

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. 

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. ... 

The ions (216) can be prepared by protonation of the corresponding 2,3-homotropones in fluorosulphonicacid. Irradiation (A > 360 nm, — 70°C)ofthe ions leads to their isomerization. The selectivity shown in the photoisomerizations is attributed to the circumambulatory migration of the C-8 group via intermediates such as (217—219). Photoisomerization about the C-1—O and about the C-2—C-3 bond of the allyl cations (220—222) has been reported cf. the earlier preliminary report. Childs has reviewed the photochemical reactions of protonated unsaturated compounds. 

Bromine has been reported to react with 2,3-homotropone by two competitive mechanisms, affording mainly the dibromides (394) and (395). With thionyl chloride. 

Dibromo-3,3,6,6-tetramethylcycloheptanone reacts with potassium t-butoxide in THF to give the stable cyclopropenone (238). 2,3-Homotropone has been prepared from cyclo-octa-l,3,5-triene by bromination to give 1,6-dibromocyclo-octa-2,4-diene, oxidation to 6-bromocyclo-octa-2,4-diene-1-one, and cyclization. ... 

While pyrazolines derived from tropone and diazo-alkanes are stable only to -10°C, their analogues produced from iron-co-ordinated tropone are stable to 80 °C, at which temperature decomposition ensues and, after demetallation, an exo-endo mixture of homotropones (126) is obtained in high (>90%) yield. The CIS- and trans-divinylpyrazolines (127) are also thermally labile, and at temperatures... 

Cyclodimerization of 3,3-dimethylcyclopropene is generally catalysed by Lewis acids, while with a palladium(o) catalyst, and in the presence of carbon monoxide, syn,anti,syn-hexamethyl-tris-a-homotropone is produced in 90% yield. ... 

Cyclo-octa-l,2,4,6-tetraene has been generated by photolysis and thermolysis of the sodium salt of 2,3-homotropone p-toluenesulphonyl hydrazone. When generated photolytically, it could be trapped by cyclopentadiene but not by furan, and in the... 

Diazomethane with tropone at 0°C has been shown to give a mixture of products, including 2,3-homotropone and pyrazolotropones. The equilibrium (95) (96) in Scheme 11 was shown to be so preponderantly towards (95)... 

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