Quinones azulene

Azulene quinones [49b] are compounds related to the family of tropones and are considered to possess great biological and physiological potential. Several polycyclic compounds have been prepared by high pressure (3kbar, PhCl, 130°C, 15h) Diels-Alder reaction of 3-bromo-l,5-azulene quinone (137) and 3-bromo-l,7-azulene quinone (138) with several dienophiles. The cycloadditions were regioselective and afforded cycloadducts in reasonable to good yields (Scheme 5.20). 

The product of this synthesis is an especially useful, highly functionalized hydroazulene that is not available commercially. We have used it as a synthetic precursor to homoazulene,5 and to a variety of homoazulene derivatives,6 bridged homotropylium cations,7 and azulene quinones.8 It could undoubtedly serve as a precursor to numerous natural products. The cyclization reaction tolerates electron-donating substituents3 9 but not halogens10 on the aromatic ring. 

Mori et report that the azulene quinone (276) in methylene chloride solution undergoes photochemical dimerization on irradiation using a 400 W mercury arc lamp. Three products were isolated from this process and were identified as (277), (278) and (279) in 6, 10 and 24%, respectively. The outcome of the reaction shows some dependence upon the solvent used for the irradiations. A time-resolved single photon study of the photophysics of hypericin and its methylated analogues has been reported. ... 

Crystal structures of triptycene-l,4-quinone and its photoproduct have been determined. A full account of the photochemical reactivity of azulene quinones... 

The reactions of 534 with substituted quinones produced mixtures of regioisomers. The substituent effect on the regioselectivity of the [8 + 2] cycloaddition reactions was said to be dependent on steric as well as electronic effects. Equation 156 shows the reaction between 534 and 2-methylbenzoquinone (539). The reaction afforded a mixture of two regioisomeric adducts 540 and 541, which were transformed to azulenes 542-545 under the reaction conditions applied318. 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

Aerial oxidation of this affords anthraquinone in 37% yield. Both 1-naphthyl and 2,4-dimethylbenzene sulphonates follow the same path but yield only traces of the corresponding quinone. In the last case, 2,4-dimethylbenzenesulphonate, the quinone is accompanied by 0.8% of 2,4-dimethylphenol. The second path involves loss of sulphur trioxide to yield aryl radicals which afford the products, the arene and/or the biaryl, shown in Scheme 17212,213. Other studies have shown that anthraquinone-1-sulphonic acid (256)214,215 and anthraquinone-2-sulphonate216 are also photochemically labile. A study of the photochemical reactivity of azulene sulphonic acids has also been reported217. Photochromism has been studied with respect to the stilbene derivative 257218. 

The oxidative formation of azulenoquinones from linearly fused azulenoheterocycles, on the other hand, exactly follows the rules of electrophilic substitution on azulenes (cf. Section 4.2.1). Thiophene 45a or furan 47a (Scheme 68) can be oxidized by bromine/aqueous acetic acid, phenyltrimethylammonium perbromide (PTAB) or pyridinium perbro-mide to yield mixtures of quinones 274a and 275a or 274b and 275b, respectively (96BCJ1149, 03H(61)271). 

The use of Cr(0)-promoted 6 r - - 2 r-cycloaddition in the synthesis of pharmacologically active natural products has been reviewed. The 6 -I- 3-cycloaddition of dimethylaminofulvene (194) with benzoquinones provides an efficient route to the 3-oxabicyclo[4.3.0]nonane system (195) (Scheme 76). Density-functional theory calculations provide evidence for a feasible concerted antara-antara cycloaddition for the 6-I-4-reaction of c -hexa-l,3,5-triene with buta-1,3-diene. Azulene-1,5-quinones (196) and azulene-l,7-quinones undergo a variety of 6-1-4- and 2-1-4-cycloaddition reactions with cyclic dienes and cycloheptatrienes to produce cycloadducts, e.g. (197) and (198) (Scheme 77) ... 

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