Benzo tropone

The betaines 170 (R = Me, 2,4-dinitrophenyl) are reactive 1,3-dipolar-species. With electron-deficient olefins they give tricyclic adducts (172). Acetylenes and diethyl azodicarboxylate give similar adducts (173 and 174) (Scheme 7). Menschutkin methylation of 172 gives the methiodides (175) which undergo Hofmann elimination to 2-dimethylamino-6,7-benzo-tropones (177) (Scheme 7). The benzocycloheptadienones (176) are not... 

Both the 2,3-benzo- and 4,5-benzo-tropones show marked alternation of bond lengths in their seven-membered rings [242]. It was early noticed that 4,5-benzotropone did not form an oxime or a phenylhydrazone [123]. 2,3-Benzotropone forms a 2,4-dinitrophenyl-... 

The structure of the product was not recognised then, but was established when the work was repeated in 1953 [121]. 4,5-Benzo-tropone was first prepared in 1909 [122,123] and its alkyl derivatives even earlier in 1906 [123,124]. 

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... 

Preparation the linear tropone-annelated benzo [c] furans 371 (X = O) by direct condensation of dialdehyde 370 (X = O) with acetone, 1-phenyl-acetone, and 1,3-diphenylacetone, in alkaline medium was—in contrast to the corresponding benzo [c]thiophene (X = S)—unsuccessful. Interestingly, this condensation has been brought about with the Diels-Alder adduct 372 subsequent heat yields 371 (X = O), a rare case where V-phenylmaleimide is used as a protective group. Compounds 371 react with V-phenylmaleimide even at room temperature to give adducts 373. 

The physical properties of the borepins mentioned above have been compared with those of other seven-membered cyclic compounds. It was concluded that a ring current is present in (56), causing a deshielding of its protons in the NMR spectrum. Benzo and dithieno fused borepins have UV spectra very similar to the correspondingly fused tropones, thus suggesting similar electronic structures. 

In oxepinotropone 147b, the heteroring protons (H-2-H-5) appear at a lower field than those in 1-benzoxepine. In the tropone ring, the a-protons (H-7, H-9) resonate at low field while the /3-protons (H-6, H-10) are observed at higher field than those of benzo[d]tropone [94H(38)957],... 

In the series of heterocyclic fused analogs, Cook et al. (68T4501, 68TL3771) compared the properties of cyclohepta[c]furan-6-one (307a) with those of benzo[d]tropone and tropone by means of HMO calculations, spectra, and chemical reactivity (carbonyl derivatization). Whereas the two fused systems are comparable, their aromatic character is still less than that of tropone. 

Furthermore, Trinajstic and co-workers [68MI1 71ZN(B)1007] reported the results of calculations (HMO, SCF) that support bond-alternating structures for the seven possible furotropones. Each shows less delocalization energy and less aromatic stabilization (As) than benzo[h]- and benzo[<7]tropone. 

The tropolone carbonyl group does not give ketonic derivatives unless the aromaticity of the ring is much decreased, as in some benzo-fused tropolones (68MI2, p. 370). Pyridotropolones like 373 (65MI3), apparently having a 1,2-diketone structure (eventually 389), afford dioximes, dihydra-zones, osazones, and quinoxalines (Section IV,A,6,a). Their methyl ethers show the normal tropone reactivity. 

Next, other unsaturated carbocyclic systems are discussed, such as dibenzo-cyclo-heptadienes ( atropisomeric biphenyls), dihydropleiadenes, cycloheptatrienes and their benzo-derivatives. Most of these compounds exist in a half-boat or boat conformation. Tropones are considered in the light of recently published work. 

The usual conversion of benzosuberanone (1) into benzo[2,3]tropone (3) involves two bromination and dehydrobromination sequences with moderate yield. Collinton... 

Irradiation of tri5(2-benzo[b]thienyl)methyl alcohol (153) in acetonitrile is reported to yield the tropone derivative (154) and the cyclopentanone (155). The tropone is considered to arise by cyclization of the three thienyl rings as... 

See Table IX, Footnote (a). b IO = isooctane, CH = cyclohexane. cd Parent tropone and tropolone, respectively. Benzo[d]tropone (numbered like type 304). Quaternary salt (2,3-dimethyl-8-oxocycloheptoxazolium perchlorate, 507 63UP2) Amax(log e) 243 (4.28) and 333 (3.93), region A 492 (2.62), region B. 

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