Benzo tropolones

Arpin, N., J. Favre-Bonvin, and W. Steglich Le Fomentariol Nouvelle Benzo-tropolone Isolee de Pomes fomentarius. Phytochem. 13, 1949 (1974). 

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. 

In contrast to unsymmetrically substituted monocyclic tropolones (which usually give two isomeric derivatives), both benzo- and heterocyclotropo-lones form only one product, owing to the resonance inhibition of the tropolone ring. 

Rings with one heteroatom are [6]-fused unless otherwise stated. h The numbering used is that of bicyclic systems (295, 296). Tropolones. d- / Also antistrychnine, antiallergic, or cardiovascular agents, respectively. 8 See 90H(31)677 94JHC1557. h 67/-Benzo[5,6]cyclohept[ 1,2,3-cd]indoline-1,6-diones. 1 See 91MI1. 

Benzo f tropolon 7-Brom- V/2c, 736 Cyclohutene 2-Brommethyl-3,4-dioxo-1-phenyl- E17f, 1000 (H - Br)... 

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. 

The first synthesis of a benzotropolone (or indeed of any tropolone) was carried out in 1949 by dehydrogenation of 1,2-benzo-cycloheptene-3,4-dione to give 3,4-benzotropolone [243,328],... 

The synthesis of Eschenmoser (Scheme 11.11) took its start with an easily accessible compound, purpurogallin, which has a benzo-anellated seven-membered ring system (incidentally, a tropolone system as well). The main challenge was the position-specific anellation of the second seven-membered ring. The Diels-Alder approach chosen required the presence of two ester groups (Add EG), that had to be subsequently removed. The tropolone arrived at in this manner had unfortunately an incorrect placement of oxygen... 

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