Aromatic 1,4-diketone

The synthesis of a soluble nonacenetriquinone based on the well-known Diels-Alder reaction of 1,3-diarylisoben-zofurans was developed by L.L. Miller and co-workers. The preparation of the 1,3-diarylisobenzofuran commenced with the Paai-Knorr furan synthesis. The substrate was an aromatic 1,4-diketone, which was treated with excess neat boron trifluoride etherate for almost two days to afford the desired 2,5-diarylfuran in almost quantitative yield. Interestingly, this cyclization could not be achieved efficiently by using the more traditional acid catalysts such as H2SO4 or PPA. 

The Wittig-Horner procedure, starting from bisphosphonate or aromatic bisphosphine oxide monomers, allows for AA/BB-coupling of the PO-activated bismethylene monomers, not only with aromatic dialdehydes but also with aromatic diketones to the corresponding PPV derivatives (76), and for the selfcondensation of AB-type aromatic starting compounds containing both alde-hyde/keto and PO-activated methylene functions [101]. 

Intramolecular coupling Some aromatic diketones have been stereoselectively cy-clized under various electrolysis conditions, which, together with the substrate structure, strongly influence the stereochemistry of the formed cyclic diol. Reductive cyclization of 1,8-diaroylnaphthalenes led to trans-diols, 2,2 -diaroylbiphenyls and a, )-diaroylalkanes yielded cis-diols with different stereoselectivities depending on substrate structure and electrolysis conditions (pH, cosolvent) (Fig. 57) [310-312]. 

Excellent yields of adduct have been obtained from a variety of o-quinones, including o-benzoquinone, 1,2-naphthaquinone, phen-anthraquinone, 5,6-chrysenequinone, and many of their simple derivatives, including the heterocyclic quinone 326 benzo[A]quinoline-5,6-quinone. Lower yields are in general observed for aromatic diketones such as benzil,327 and the reaction does not appear to occur to any appreciable extent with aliphatic a-diketones. 

These distonic superelectrophiles (145-147) have been characterized by low-temperature H NMR (and 13C NMR in the case of 147) from FSO3H-SbFs solution. Dication 146 was also studied by calorimetric studies to determine the heat of diprotonation of 2,5-hexanedione.48 It was found that the heat of diprotonation for the y-diketones (like 2,5-hexanedione) is about 5 kcal/mol less than expected, when compared to twice the heat of protonation of acetone or other monoketones. The destabilization of dication 146 by 5 kcal/mol can be the result of electrostatic effects, and it can be considered evidence for the superelectrophilic character of such dications. When 2,6-admantanedione is reacted in FSO3H—SbFj solution, the dication 148 is formed as a persistent species, observable by and 13C NMR.12 The carboxonium carbons of 148 are observed at Z I3C 247.7, while the mono-cationic species (149) has a carboxonium carbon at 513C 267.1. These 13C NMR data were interpreted as evidence for the increasing importance of the carboxonium-type resonance structure (148a) due to electrostatic repulsive effects. Some examples of aromatic diketones (i.e., diacetylbenzenes) have also been reported to produce bis-carboxonium dications in their protonation reactions in superacids.47... 

During the study of dithiiranes, thionations with Lawesson s reagent (LR) in refluxing 1,4-dioxane converted the aromatic diketone 229 into a 1,3-dithietane 230 (main product) and a 1,2,4-trithiolane 231 (Equation 15) <1997BCJ509>. 

Oxazole IV-oxides cannot be made by oxygenation of oxazoles. The only method of synthesis remains the condensation of monooximes of 1,2-dicarbonyl compounds with aldehydes in the presence of hydrogen chloride (equation 132) (15CB897). The aldehyde may be aromatic or aliphatic (including formaldehyde) and the oxime may be derived from an aromatic diketone or it may be an a-keto aldoxime, leading to a 2,5-disubstituted oxazole IV-oxide. It may also contain an additional carbonyl group as in equation (133). 

Benzile.—The aromatic diketone benzile, CeHsCO-CO-CeHs, gives peculiar results (Kauffmannx). By reduction in an alkaline alcoholic solution a whole series of bodies is formedy i.e., benzoic acid, benzilic acid, tetraphenylerythrite ... 

The photocycloaddition of aromatic diketones [98] to furan and tetramethylallene was studied by D.J. Andrews and W.J. Feast (177). The results are given in Table 15. 

Equally smooth is the reduction of aliphatic, alicyclic, and aromatic diketones to diols by the equivalent amount of complex boron hydrides. For instance, excellent yields of, mainly, m so-diols are obtained from acyclic 1,3-diols.389 The preparation of /ra .s-5-hydroxy-4a-methyl-zl1 8a-octalin-2-one from the corresponding dione by NaBN4390 is an example of selective reduction of one keto group of a dione ... 

The reaction is applicable to almost all aromatic diketones, but in the aliphatic series it is restricte4 to isolated cases.164 When carrying out the benzilic acid rearrangement it is necessary to ensure that the diketone is free from cyanide, because Dilthey and Scheidt165 have shown that in the presence of cyanide ions benzil is cleaved hydrolytically to benzaldehyde and benzoic acid. 

Benzil, CeHs.CO.CO.CeHs, is an aromatic diketone. It is most conveniently prepared by oxidizing benzoin (585) with nitric acid —... 

The photoreductive dimerization of aromatic diketones to high-molecular-weight poly(benzpinnacols) is an example of the involvement of a reactive ground state produced by a photochemical reaction ... 

The Japp oxazole synthesis is the reaction of 1,2-aromatic diketones 1 and aromatic aldedhyes in the presence of ammonia to form oxazoles... 

The 1,2-diketone 1 can be converted into the salt of an a-hydroxy carboxylic acid upon reaction with alkali hydroxide, which upon acidic workup affords a-hydroxy carboxylic acid 2. Semi-aromatic diketones, aliphatic, heterocyclic and aromatic diketonesundergo this rearrangement. The substituents should not bear hydrogens a to the carbonyl group, to avoid competing reactions such as aldol condensation. 

InClj (10 mol%) 80 °C, excellent yield, aliphatic as well as aromatic diketones used 69... 

Ortho quinones (and also aromatic a-diketones, o-phenylenediamine to yield quinoxalines as follows. 

Diketones and tetraketones derived from aromatic compounds by conversion of two or four SCH groups into keto groups, with any necessary rearrangement of double bonds to a quinonoid structure, are named by adding the suffix -quinone and any necessary affixes. 

Synthesis and Properties. A number of monomers have been used to prepare PQs and PPQs, including aromatic bis((9-diamines) and tetramines, aromatic bis(a-dicarbonyl) monomers (bisglyoxals), bis(phenyl-a-diketones) and a-ketones, bis(phenyl-a-diketones) containing amide, imide, and ester groups between the a-diketones. Significant problems encountered are that the tetraamines are carcinogenic, difficult to purify, and have poor stabihty, and the bisglyoxals require an arduous synthesis. 

Aromatic aldehydes (100), eg, cinnamaldehyde, and ketones (101) react ia a similar manner (eq. 4). Ketones containing reactive methyl or methylene groups give with succiaates, ia the presence of sodium hydride, both the Stobbe condensation and the formation of diketones by a Claisen mechanism (102) (eq. 5). 

Polyfluorinated a-diketones react with 1,2-diainino compounds, such as ortlio-phenylenediamine, to give 2,3-substituted quinoxalmes [103] Furthermore, the carboxyl function of trifluoropyruvates offers an additional electrophilic center. Cyclic products are obtained with binucleophiles [13, 104] With aliphatic or aromatic 1,2-diamines, six-memhered heterocycles are formed Anilines and phenols undergo C-alkylation with trifluoropyruvates in the ortho position followed by ring closure to form y-lactams and y-lactones [11, 13, 52, 53, 54] (equation 23). 

---