Cyclohepta furans

Quaternary ammonium tribromides in methanol-dichloromethane did not brominate the furan ring of 3-methyl-8//-cyclohepta[/>]furan-8-one. Instead, the 7-bromo derivative was formed (92BCJ295). 

On the other hand, the anodic oxidation of 1,3,5-cycloheptatrienes is one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 27/-cyclohepta[ ]furan-2-ones and azulenes. ... 

Treatment of the furotropone (105) with the keten (106) leads to the furo-heptafulvalene (107). 2//-Cyclohepta[ )]furan-2-one (108) undergoes twofold [Stt + 27t] cycloaddition to 6,6-dimethylfulvene to yield, after loss of carbon dioxide, the diazulenofulvene (109), accompanied by the rearranged azulenonaphthofulvene (110). ... 

The intramolecular 8 -I- 2-cycloaddition of heptafulvene-fulvene (199) produced the intermediate adduct (200) which converted into the product (201) by 1,5-sigmatropic shifts in 46% yield (Scheme 78). 2-Oxo-27/-cyclohepta[ ]furan derivatives (202) undergo 8 -I- 2-cycloaddition with dienes to yield cycloadducts (203) in high yields (Scheme 79) ° Ab initio calculations on the cycloaddition of tropone with maleic anhydride favour the 4 - - 2-endo pathway while calculations of tropothione with maleic anhydride favour the 8 -I- 2-endo pathway. ... 

H-Cyclohepta[ ]furan-2-one 478 and related compounds undergo electrophiUc substitutions at the 8-position of the fulvenes [288]. Heteroazulene-substituted tropylium ions 479 are prepared by the reaction of 478 with tropylium ion (Scheme 6.126a) [288]. Nitta and coworkers [289] synthesized ketones 480,... 

Ethynylated 2/f-cyclohepta[()]furan-2-ones 486 are prepared by Pd-catalyzed alkynylation of 3-iodo-5-isopropyl-2//-cyclohepta[ ]furan-2-one 487 with the corresponding ethynylarenes [292]. The compound reacts with tetracyanoethy-lene (TCNE) 488 and TCNQ 25 to afford highly polarized dicyanoethylene derivatives 489 and 490 respectively (Scheme 6.128) [293]. 

Benzo[15]crown-5, potassium complex X-ray, 7, 735 (B-78MI52102) 10H-Benzo[5,6]cyclohepta[l,2-b]furan, 4,5-dihydro-... 

H-Benzo[a]carbazole, 4,4a,5,l 1,1 la,l Ib-hexahydro-synthesis, 4, 283 Benzo[b]carbazole, N-acetyl-photochemical rearrangements, 4, 204 Benzo[/]chroman-4-one, 9-hydroxy-2,2-dimethyl-synthesis, 3, 851 Benzochromanones synthesis, 3, 850, 851, 855 Benzochromones synthesis, 3, 821 Benzocinnoline-N-imide ring expansion, 7, 255 Benzocinnolines synthesis, 2, 69, 75 UV, 2, 127 Benzocoumarins synthesis, 3, 810 Benzo[15]crown-5 potassium complex crystal stmcture, 7, 735 sodium complex crystal stmcture, 7, 735 Benzo[ 18]cr own-6 membrane transport and, 7, 756 Benzo[b]cyclohepta[d]furans synthesis, 4, 106 Benzocycloheptathi azoles synthesis, 5, 120... 

A very elegant formation of heptafulvenes from triafulvenes was found by Gompper294 utilizing the push-pull stabilized cyclobutadiene 511 in the case of 1,2-diphenyl-4,4-diacetyl triafulvene (180) the 4-acyl group caused additional ring closure yielding cyclohepta(b)furan 514 ... 

Aminopyrans, annulated directly with a seven-membered carbo-cycle, are very rare. One, 139, is formed from substituted cyclohepta[c] furan-4-one 140 with UNs 30 (08CFIE136) (Scheme 50). 

Nomenclature according to Tochtermann et Strictly speaking, compounds of type 368 (X = CO) and 369 should be named from furan as the base system (8Ff-dibenzo[3,4 6,7]-cyclohepta[l,2-c]furan-8-one). 

Intramolecular attack of the carbenes (25) provides benzo[fr]cyclohepta[d]-furans and -thiophenes (26 X = 0, S). Photolysis of 2-biphenyl isocyanide (27 — 28) (72JOC3571) and thermolysis of 2-biphenylsulfonyl diazomethane (29 — 30 — 31) (72CC893) also result in ring expansion. 

The PE spectra of 6H-cyclohepta[c]furan-6-one (and molecular orbital calculations on this system) have been reported (84BGJ856). 

Acenaphthylene, indene, and styrene undergo periselective 4 + 2-cycloaddition with 3-ethoxycarbonyl-2//-cyclohepta[Z>]furan-2-one in high yield.152... 

In 5,7-polymethylene derivatives of cyclohepta[c]furan-6-ones, the C=0 band is shifted from 1682 down to 1628 cm1 on lengthening the ansa chain from 7 up to 10 members (85MI3). 

In a unique pathway, cyclohepta[fo]furan-6-ones such as 404a (Scheme 95) first lose CO from the tropone or from the furan rings (94RRC41). 

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. 

Intramolecular attack of the carbenes 32 provides benzo[7]cyclohepta[<7] furans and thiophenes 33 (Scheme 15). Photolysis of 2-biphenyl isocyanide 34 (Scheme 16) <1972JOC3571> and thermolysis of 2-biphenylsulfonyl diazomethane 35 (Scheme 17) <1972CC893> also result in the formation of ring expanded products. 

A further example is the reversible valence isomerization equilibrium between the dipolar 8,8-diformylheptafulvene (41a) and the less dipolar 8a//-cyclohepta[Z)]furan-3-carbaldehyde (41b) [212]. 

The 8 + 2-cycloaddition of 2//-cyclohepta[Z>]furan-2-one (155) with acyclic 1,3-dienes provides a facile route to hicyclo[5.3.0] ring systems (156) (Scheme 61). 2H-Benzo[h]thiete in the o-quinoid form undergoes 8- -2-cycloaddition with 1,3-dithiolane-2-thione, l,3-dithiole-2-thiones, and adamantanethione to produce 4/7-1,3-henzodithianes. ... 

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