Tricyclo nona-2,6-diene

Interestingly, flow pyrolysis of 3,4-bis(trimethylsiloxy)tricyclo[4.2.1.0 ]nona-diene gives 6,7-bis(trimethylsiloxy)-8,9-dihydroindene, but the label distribution cannot occur by any of the pathways discussed earlier and was postulated to give a different isomer after formation of the intramolecular Diels-Alder reaction (Scheme 10.23). ... 

Barbaralane 548 (tricyclo[3.3.1.04,6]nona-2,7-diene) was first described in 1967 (see Reference 80 and literature cited therein). Barbaralane and its derivatives functionalized in the C(9) position (550a,b) are degenerate Cope systems whose equilibrium can be frozen... 

This transformation was first explored by treatment of l-bromo-4-(cyanomethyl)pentacyclo-[4.3.0.02 5.03-8.04-7]nonan-9-one ethylene acetal (61) with lithium diisopropylamide in tetrahy-drofuran at 0 °C, which resulted in almost quantitative yield of an inseparable mixture of two alkenes to which the structures l-bromo-4-cyanomethyltricyclo[4.2.1.02,5]nona-3,7-dien-9-one ethylene acetal (66) and l-bromo-4-(cyanomethylene)tricyclo[4.2.1.02,5]non-7-en-9-one ethylene acetal (67) were assigned.170,171 As illustrated below, the overall cage-degradation reaction can be mechanistically represented by the stepwise C —C bond fission reactions, whose driving force can be attributed to the apparently substantial reduction in cage constraint. 

To an ice-cold (0°C) solution of LDA (2.5 mmol) in. THF (10 mL) was added (4-(l-bromopentacy-clo[4.3.0.02,5.03,8.04 7]non-9-onyl ethylene acetal)methyl phenyl sulfone (68 0.2 g, 4.9 mmol). After stirring at 0 JC for 10 min H20 was added and the mixture was extracted with Et20. The extracts were washed with dil HC1 and dried (MgS04). The solvent was removed to give l-bromo-4-(bcnzcncsulfonyl-methyl)tricyclo[4.2.1.02 5]nona-3,7-dien-9-one ethylene acetal (69) as an oil which solidified partly yield 0.2 g ( 100%) mp 151-153 JC (CC14). 

A clean eiectrocyclic ring opening occurred at mild temperatures with the strained tricy-clo[4.3.0.07-9]nona-2,4-diene (3a) and tricyclo[4.4.0.02 5]deca-7,9-diene (3b) to give cycloocta-1,3,5-triene derivatives 4.182... 

Similar geometric optimization has been reported for bicyclo[3.2.2]nona-6,8-diene (BND). The double bond situated in the opposite direction to the methylene group was found to be more exo-pyramidalized than the other double bond and the electron density (qi, HOMO) of the former double bond in HOMO of the molecule higher than that of the latter double bond. The exo and endo faces of exo-pyramidalized double bonds proved not to be equal and the electron density was found to be higher on the endo faces. The endo molecular complexes with bromine have been found by the HF/321G method to be more stable than their exo congeners this was attributed to electronic and steric factors. As a result, endo-facial stereoselectivity of bromination ( ) predominates.21 A related theoretical study of facial selectivity and regioselectivity of the electrophilic addition of chlorine to exo-tricyclo[4.2.1.02,5]nona-3,7-diene (exo-TND) has also been reported.22... 

The irradiation of 8-thia-l-aza-bicyclo[4.2.1]nona-2,4-diene 8,8-dioxide 125 with 350nm ultraviolet (IJV) light in pure acetone resulted in the formation of 2-thia-6-aza-tricyclo[5.2.0.01,4]non-8-ene 2,2-dioxide 60 in 52% yield <20040L1313>. However, photopolymerization occurred as a side reaction, but this can be prevented by the use of acetone with acetonitrile (2 1) as a solvent, although the yield diminished significantly to 28%. The authors proposed a mechanism for this reaction (Scheme 20) <20040L1313>. 

The exo-tricyclo[4.2.1.0 - ]nona-3,7-dien-9-yl cation [381] has been reported as an intermediate in the acetolysis of a/ir/-tricyclo[5.2.0.0 - ]nona-3,8-dien-6-yl tosylate [382] in which the acetate [383] is formed as product (Coates and Yano, 1973). The predicted ring expansion (245) of the strained ring system... 

Barbaralyl or tricyclo[33.. (fi ]nona-3,6-dien-9-yl cations and bicyclo[3.2.2 ona-3,6,i-trien-2-yl cations... 

Benzo-tetracyclo[4.3.0.02,9.03,s]non-7-en exo- El 9b, 280 (Carben + En) Benzo-tricyclo 3.2.2.02 4 nona-6,8-dien E19b, 280 (Carben + En) 8,9-Benzo-tricyclo 5.2.0.02,s[nona-3,8-diene E17f, 673 (Benzo-bicyclo-trien/hv)... 

At low photochemic conversions the reversible transformation to the (2D hexatriene may dominate. However, the composition of the photostationary state depends upon the substitution pattern of the cyclo-hexadiene which controls the preferred conformation. It is believed that a planar 1,3-cyclohexadiene produces preferentially a bicyclo[2.2.0]hex-2-ene, e.g. molecules of the type (374), while dienes with skewed structures form hexatrienes. Another factor that changes dramatically the composition of the photolysis mixture is the wavelength of irradiation. At 254 nm the photostationary state mixture of cis-bicyclo[4.3.0]nona-2,4-diene (58) and ( ,Z,Z)-l,3,5-cyclononatriene (59) is 40% and 60%, respectively. At 300 nm, irreversible formatitm of tricyclo[4.i0.0 ]non-3-ene (374) becomes the preferred pathway. The ratio of extinction coefficients of (58) and (59) at the wavelength used would explain the shift in the photoequilibrium mixture. ... 

The hydrocarbon tricyclo[3.3.1.0 ]nona-3,6-diene(barbaralene), 296, underwent rapid exchange between structures of equal energy such that at room temperature, the activation parameters were calculated . ... 

Bicyclo[2.2.2]octa-2,5-diene and tricyclo[3.2 2.0 " ]nona-6,9-diene derivatives react with palla-dium(II) acetate in the presence of sodium acetate in anhydrous benzene to give the formal homo-Diels-Alder cycloadducts 16 and 17 of dehydrobenzene. ... 

Trapping of less stable valence tautomers with benzylideneacetone(tricarbonyl)iron [BDA-Fe(CO)3] was applied to bicyclo[6.1.0]nonatriene (40a) and its i>> -9-methyl derivative (40b). Reaction with BDA-Fe(CO)3 gave three products, one of which was a complex of tricyclo[4.3.0.0 ]nona-2,4-diene 41. As the major product tricarbonyl(tricyclo[4.3.0.0 ]... 

Teatment of cyclooctatetraenetricarbonyliron complexes 10 with anhydrous aluminum trichloride in benzene gives tricarbonyl(2,4- j-8-or-9-oxabicyclo[3.2.2]nona-2,6-dien-8-yl)iron (11), which was previously obtained from tricyclo[3.3.1.0 ]nona-3,6-dien-9-one (12 barbaralone) with nonacarbonyldiiron. Conversion of this product 11 with carbon monoxide (100 atm, 120°C) yields barbaralone (12) in 95% yield. Thus, a high yielding (95%), short synthesis of barbaralone (12, R = H) from cyclooctatetraene via an alkyl-allyl complex intermediate 11 is available. 

Other base-catalyzed ring enlargements include the reductive rearrangement of diethyl-bicyclo[4.1.0]hept-3-ene-l,5-dicarboxylate to diethylcyclohept-5-ene-l,5-dicarboxylate promoted by lithium in liquid ammonia (Section 2.4.1.5.2.6.). 9-Vinyl- and 9-arylbarbaralan-9-ols [9-substituted tricyclo[3.3.1.0 ]nona-3,6-dien-9-ols] 18 undergo retro-Diels-Alder reactions to give cycloheptadiene derivatives 19 on treatment with potassium hydride and 18-crown-6 in tetrahydrofuran. ... 

Surprisingly, /ranj-tris-a-homobenzene (eni/o/exo-tetracyclo[6.1.0.0 . 0 ]nonane), and its hexamethyl derivative, at elevated temperatures (380-400°C in a flow system and 120°C, respectively) rearrange to frani-bicyclo[4.3.0]nona-3,7-diene and hexamethyl-rra 5-tricyclo[4.3.0.0 ]non-3-ene. It was shown by isotopic labeling, however, that this rearrangement also proceeds by way of a [ 2 + A -t- cycloreversion, which in these cases leads to highly reactive cis,trans,trans-cyclonona-l,4J-tnenes, which undergo a subsequent intramolecular [2-1-2] cycloaddition. ... 

Various bi- and oligocyclic ring systems, such as norcaradiene (1 bicyclo[4.1.0]hepta-2,4-diene), bicyclo[6.1.0]nona-2,4,6-triene (2), bullvalene (3 tricyclo[3.3.2.0 ]deca-3,6,9-triene), semibul-Ivalene (4 tricyclo[3.3.0" ]octa-2,7-diene), barbaralone (5 tricyclo[3.3.1.0 ]nona-3,6-dien-10-one) and many other systems containing divinylcyclopropane subunits, exhibit interesting transition metal mediated reaction pathways leading to new carbon skeletons. ... 

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