Cyclic diones

The dione 174 only underwent oxidative coupling under Hay s conditions62 and afforded the cyclic dione 175. 

Cyclic diones or silylmethyl-protected diones react with olefines in a [2+2] fashion. Addition of these compounds to Cjq [341] leads initially to the cyclobutane fused fullerenes, which are not stable and are readily oxidized and rearranged to the furanylfullerenes 300 and 301 (Scheme 4.56). The intermediate 299 probably reacts by either intermolecular oxidation with 2 to yield 300 or by an intramolecular oxidation with the triplet fullerene moiety to yield 301. 

Scheffer, Trotter, and co-workers have provided elegant demonstrations of the distance and angular dependence between a carbonyl oxygen atom and a gamma hydrogen atom on the ease of initial abstraction [276], Their singlecrystal X-ray structural information allows the various courses of Norrish II reactions of neat solids to be understood in the context of topochemical control [11,13]. For instance, they have noted that the cyclic diones 77 (n = 7,8,10, and 12) follow different Norrish II pathways depending upon the conformations of the individual molecules in their crystals (Eq. 9) [277]. 

As discerned from Table 9, the photoproduct ratios from irradiation of neat 77 vary drastically among homologues and with temperature for the n = 7 member, Unlike the n-alkanones discussed previously, the cyclic diones must be intrinsically bent as shown in the ORTEP drawings in Figure 43. Since the C=0- H, distance in each case is <3.0 A, excitation of the molecules should result in formation of hydroxy-1,4-biradicals. The fate of those radicals depends upon the flexibility of the reaction cavity and its free volume. The results indicate that sufficient free volume is present in the reaction cavities to allow topochemical conversion to photoproducts, but not... 

Fig. 7-30. Examples of proposed leucochromophoric and chromophoric structures. Aryl-coumarones (1) and stilbene quinones (2) are thought to be formed from stilbenes after oxidation. Butadiene quinones (3) could arise from oxidation of hydroxyarylbutadienes being formed from phenolic pinoresinol structures during kraft or neutral sulfite pulping. Cyclization may yield intermediates which are further oxidized to cyclic diones (4). A resonance-stabilized structure (5) results from the corresponding condensation product formed during pulping. o-Quinoid structures (7) are oxidation products of catechols (6) formed during alkaline or neutral pulping processes.

Hydration of 85 catalysed by acid and Hg(II) gave the cyclic ether 83 directly10 and oxidation with selenium dioxide gave the cyclic dione 82 which was stable as its crystalline dihydrate 86. There is again no ambiguity of enolisation. 

Cleavage of cyclic diones by reactions 1 or 2 might be a fast, reversible process (after necessary spin inversion if triplet states are involved) and,... 

Enolizable 1,3-dicarbonyl compounds are not reduced by the Meerwein-Ponndorf-Verley reaction4,13. However, 1,2-cyclopentanedione56 and 1,2-cyclohexancdione 7 are converted to the corresponding 1,2-diols. The reaction of both cyclic diones predominantly leads to the corresponding cis-diols. The cis trans ratio depends on the ratio of substrate/aluminum isopro-poxide as shown in the following two tables. 

Analogously, from a cyclic dione (e.g. 626) by means of Me3SiCl in the presence of pyridine plus a powerful silylating agent like Na-bis(TMS)amide (405a), the reaction product is a vicinal bis-trimethylsiloxydiene (e.g. 628) (equation 321)356. In a related... 

Quinones - Compounds having a fuUy conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of -CH= groups into -C(=0)- groups with any necessary rearrangement of double bonds. [5]... 

In biacetyl, the situation is somewhat different from the aforementioned cyclic dione. The presence of a treely rotating bond between the second and third carbons allows the biacetyl to assume the more stable S-trans conformation, thereby reducing the electrostatic interactions of the carbonyl groups. 

In 2008 Chandler and List found that (2S,4/ )-4-fluoroproline (trans-27e) was the most effective catalyst for the asymmetric transannular aldolisations of cyclic diones and exploited it in the total synthesis of (+)-Hirsutene (Scheme 11.23). ... 

Scheme 11.23 Asymmetric transannular aldolisations of cyclic diones using catalyst trans-27e.

Tu et al. have reported the synthesis of 4-aza-podoplyllotoxin via a three-component reaction of an aldehyde, aniline and cyclic diones in H2O under MWl. Use of tetronic acid as the cyclic diketone provided the 4-aza-podophyllotoxin derivatives (76) (Scheme 6.30). The reaction proceeded via the attack of Schiff s base, formed through the condensation between aldehyde and aniline, on tetronic acid resulting into an intermediate which underwent intramolecular cyclization and dehydration to yield the product. The scope of the strategy was enhanced by replacing tetronic acid with 1,3-indanedione to generate indenoquinoline derivatives (77) [69]. 

Quinones - Compounds having a fully conjugated cyclic dione... 

The Shvo catalyst 1 was successfully used in the transfer hydrogenation of 1,3-diones to the corresponding 1,3-diols with isopropanol as the hydrogen donor (2) [36, 37], This reaction is synthetically useful for the reduction of cyclic diones since reduction of these diketones by LiAlIli preferentially gives the aUyUc alcohol [36]. Also piperidine-3,5-diones were efficiently reduced to the corresptMiding diols by isopropanol using 1 as catalyst [37], and these diols were subsequently used in dynamic kinetic asymmetric transformatimis (DYKATs) to provide stereodefined 3,5-disubstituted piperidines [36, 37],... 

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