Tropones, substituted

The parent TMM precursor (1) reacts with tropones (117) to give reasonable yields of the bridged [4.3.1]decanones (118) [43]. Various substituted TMMs also cycloadd to tropone with regioselectivity similar to that of the corresponding [3+2] cases [20, 43]. Addition of MesSnOAc as a co-catalyst also leads to yield improvement [16]. In the case of a phenyl-substituted tropone and a methyl-TMM, performing the reaction under high pressure favors the formation of kinetic products (119) and (120) over the thermodynamic product (121) [11]. 

Whereas tropones usually act as dienes in cycloaddition reactions (Section 5.4), tricarbonyl (tropone) iron 59 displays a reactivity that is almost identical to that of a normal enone. High pressure cycloadditions of 59 with 1-oxygen substituted dienes 60 gave the desired cycloadducts 61 in good to excellent yields (Equation 5.9). The subsequent decomplexation of the cycloadducts has been accomplished by treatment with CAN [20]. 

Tropone (125) and the 2-substituted tropones showed a different reactivity in the cycloaddition with 2-cyclopentenone (28). Whereas tropone itself (125) and the 2-methoxytropone (126) reacted at lOkbar, giving a mixture of four and three products, respectively (Scheme 5.18), 2-hydroxy- and 2-chloro-tropone failed to react at all [43b]. Compound 127 does not have the expected dihydro-homobarrelenone framework it is probably derived from the cycloaddition of 125 and 1,4-cyclopentadien-l-ol, the enol form of 28. 

The freeze of equilibrium by the complexation method is also applicable to some other compounds. 2-Mercapto substituted tropone 32 has been reported to exist as an equilibrium mixture of 2-mercaptotropone (32 a) and 2-hydroxytropothione (32 b), and the latter is predominant both in solution 17) and in the solid state 18). The equilibrium is frozen and the former was isolated by inclusion complexation with 1. When a solution of 1 and 32 in petrol ether was kept, a 1 1 complex 33 composed of 1 and 32a was obtained in 90% yield as orange prisms of mp 101 to 103 °C19). The structure of 32a in 33 was elucidated by IR spectroscopy which showed vSH at 2482 cm-1 33 gave also absorptions of a strongly hydrogen-bonded hydroxyl group at 3270 cm 1. 

Cyclopropenones are markedly more basic than other a,0-unsaturated compounds131 tropone, however, exhibits higher basicity than cyclopropenones due to its half-protonation value of —0.4. As shown in Table 4, basicity of cyclopropenones is increased by alkyl substituents relative to phenyl substitution. This is also demonstrated by the observation132 that di-n-propyl cyclopropenone is extracted by 12N HC1 from CCI4 solution, but diphenyl cyclopropenone is not. 

All the bridged [1 ljannulenones condense with malondinitrile in acetic anhydride and yield the corresponding dicyanomethanohendecafulvenes (e.g. 11 - 38) and these on treatment with strong acid furnish the substituted l,6-methano[ll]an-nulenium ions. 11 -Chloro-3,8-methano[ 11 Jannulenone 31, in parallel with the behaviour of the similarly 2-substituted tropone, undergoes reaction with sodium meth-oxide at room temperature to afford chiefly the products of normal 39 and cine substitution 40. 

Machiguchi, Nozoe and coworkers have very recently observed that in contrast to chemical reactivity of tropones, the tosylate of tropone oxime undergoes a facile ring-opening to 6-substituted (Z,Z,Z)-1,3,5-hexatriene nitriles on reaction with various nucleophiles305. For example, reaction of phenyl lithium results in the corresponding hexatriene carbonitrile (equation 183). 

In addition to 534, further [4+2]-cycloadducts of 5 were prepared by using 1,3-dienes, some of which are well known as trapping reagents of short-lived cyclic allenes and cycloalkynes. Further, cycloadditions could be achieved with tropone and several 2-substituted tropones, 8,8-dicyanoheptafulvene, 1,3,5-cycloheptatriene and a few of its 7-substituted derivatives. The products of these reactions are represented in Scheme 6.108. 

Mahon and colleagues297 studied the cycloaddition reactions of substituted cis-1,2-isopropylidenedioxycyclohexadienes. The reaction of tropone (471) with cyclohexadiene 472, for example, afforded the expected exo cycloadduct 473 with good yield (equation 140). 

In general, this approach can be represented by equations 207 and 208 wherein the formation of cis- and fraws-substituted seven-membered rings (e.g. tropones or oxepines) is controlled by selection of appropriate isomeric divinylcyclopropanes or divinylepoxides as precursors. We will discuss here a series of examples which are not covered by a recent review260. 

Ito and his co-workers (51) noticed that an adduct (14) of tropone with iV-ethoxycarbonylazepine appeared to undergo slow internal rotation by H NMR, the barrier at 83°C being 18.3 kcal/mol. As was discussed earlier, the ethoxy-carbonyl group gives a lower barrier than those of acetyl and formyl derivatives. Indeed, by changing the /V-substitutent from ethoxycarbonyl to acetyl, the barrier was raised to 20.0 kcal/mol. The formyl derivative showed a barrier to rotation of 23.0 kcal/mol at 20°C. It was possible to isolate a pure Z isomer and a nearly pure E isomer of the formyl derivative (15) by TLC. The free energy of activation... 

Several other substituted benzenes have been reacted with carbon and the substituted phenylcarbene or cycloheptatetraene have been trapped in an intramolecular reaction. Thus, phenol reacts with C atoms to give tropone (63) and traces of the 0-, m-, and p-cresols. In this case, an initial o-, m-, or p-hydroxyphenylcarbene (64) is postulated to ring expand to a hydroxycycloheptatetraene that traps itself by intramolecular proton transfer (Eq. 38). A competing reaction of 64 is... 

The substituted cycloheptane monoterpenes, also called tropones. Eu-carvone 60, nezukone (4-isopropyl-2,4,6-cycloheptatrienone) 61 and y-thujaplicin 62 (Structure 4.14) most probably arise by an unknown ring expansion of the cyclohexane skeleton. 

As mentioned in Section III,A, benzo[c]furan (4) participates in thermal [jt4 -I- TCgJ-cycloadditions. With tropone and substituted tropones, compounds of type 206 (exo R = H, Cl, OMe) have been obtained, and 6,6-dimethylfulvene yielded 207 (endo). The extended Hiickel method and... 

Interesting highly colored compounds were reported to be prepared by treatment of 2-substituted tropones with thiourea. Thus the orange or yellow 3-aza-l-thiaazulenes 227400,401 are formed from 2-chloro-tropones however, the scarlet diazaazulene 228402 was produced from a 2-methoxytropone under the influence of sodium ethoxide. 

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 TCNE adducts of a variety of other [nq4-Fe(CO)3]- complexed trienes and tetraenes have been investigated. In most cases the adducts have been oxidatively cleaved from the metal with CeIV and the free ligands recovered in good yields. Reactivity patterns generally follow those described above for cy-cloheptatriene and cyclooctatetraene complexes. Specific complexes investigated include [Fe(2,4,6-cy-clooctatrieneone)(CO)3],61 [Fe(tropone)(CO)3],62,63 [Fe(heptafulvalene)(CO)3] and various 8-substituted... 

N-Substituted benzotriazole intermediate (77) is an excellant synthon for the synthesis of 2-ethoxy-2-vinylcyclopropanecarboxylate esters (78) [95JOC6], 1-Propargylbenzotriazole was reacted with bromoacetophenone to provide the novel 2-(benzotriazolomethyl)furan (80) in 60% yield [95JOC638]. Annelated N-aminotriazoles, on oxidation, are a good source of cyclic alkynes as illustrated for the reaction of aminotriazolotropone (80) with 4-phenyloxazole to generate the furyl[3,4-cf]tropone (82) from a Diels-Alder intermediate with facile loss of benzonitrile [94TL8421 ]. 

Recently, the reaction of masked ortho-benzoquinone [92] with C60 was tested [93]. The [4+2] cycloaddition reaction of such electron-deficient dienes with fullerenes resulted in the formation of highly functionalized bicyclo [2.2.2] octenone-fused fullerenes. The reactants were generated in situ by the oxidation of the readily available 2-methoxy phenols with hypervalent iodine agents. For the several different masked ortho-benzoquinones that were tested, it was found that the yield of the cycloadducts depends on the nature of the starting materials and the reaction conditions. Other Diels-Alder reactions of such electron-deficient dienes with electron-poor fullerenes involved tropones [94], 1,3-butadienes substituted with electron-withdrawing groups [95], and 2-pyrone [96]. 

In principle, fused tropones behave similarly to their monocyclic analogs (73CRV293, p. 329). IR spectra could be used, for instance, to identify isomeric anhydrosepedonin dimethyl ethers 418a-c (Scheme 112 69MI3) and pyrazolotropones substituted at N-l (98b) or N-2 (91JHC717). Table XVII contains selected IR data of relevant compounds as assigned by the respective authors. 

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