1,4-Cyclohexanedione catalytic

The application of auxiliary control in the asymmetric Michael addition of chiral enolates derived from ketones is rare the only example known is the use of (27 ,37 )-2,3-butancdiol as an auxiliary. The ketal of (27 ,37 )-2,3-butanediol with 3-methyl-l,2-cyclohexanedione reacts with 3-buten-2-one using as base a catalytic amount of sodium ethoxide in ethanol195. 

Randin, in a recently-published paper 44>, investigated solely on the basis of results from the literature the relationship between electrocatalytic activity for 2 reduction on the one hand, and oxidation potential, magnetic moment, and catalytic properties in gas-phase reactions on the other. It was found for the transition-metal phthalocyanines that magnetic moment and activity for the dehydrogenation of cyclohexanedione increase together with the activity of the phthalocyanines for 2 reduction, while the oxidation potential becomes less. The last fact can be seen from Fig. 29, in which the first oxidation potentials in 1-chlomaphthalene, measured by Manassen and Bar-Ilan 45>, are plotted against electrochemical activity. This result shows that the more easily an electron can... 

A review by Schuchardt et al. thoroughly analyses the various catalytic systems reported in the literature up to 2000, both homogeneous and heterogeneous ones, and those that use oxidants other than oxygen [e.g., HP or t-butyl hydroperoxide (f-BuOOH)[ [2c[. The mechanism involves the formation of cyclohexanol via the cyclohexyl radical and cyclohexyl hydroperoxide. According to the Haber-Weiss mechanism, cyclohexyl hydroperoxide decomposes into alkoxy and alkyloxy radicals (Section 7.2.1). Cyclohexanol is finally oxidized to cyclohexanone. A similar mechanism may occur at the a-C, affording 1,2-cyclohexanedione, which is finally cleaved to AA. Oxidation of the intermediately formed cyclohexanone to AA then occurs through a mechanism similar to that illustrated in Scheme 7.5. 

Another synthetically useful reagent of this type is 5,5-dimethyl-l,3-cyclohexanedione phenyliodonium ylide (781) (Scheme 3.308), a relatively stable iodonium ylide synthesized by condensation of PhI(OAc)2 with dimedone under basic condition [1060,1061]. Under catalytic, thermal, or photochemical conditions, ylide 781 serves as an excellent carbenoid precursor the transfer of such a carbenoid moiety to a suitable... 

The requisite 2,5-dihydroxyterephthalic acid (DHTA) was initially prepared by bromine oxidation of commercially available diethyl succinylosuccinate (DDS also known as diethyl 1,4-cyclohexanedione-2,5-dicarboxylate) in cold sulfuric acid, followed by alkaline hydrolysis. It was later found that a more convenient and facile preparation of DHTA involved the aromatization of DSS using elemental sulfur as the hydrogen acceptor in the presence of a catalytic amount of Pd/C in boiling diethylbenzene (DEB), (see figure 8). 

They successfully developed an easy and efficient method for the preparation of various quinoline derivatives from different ketones and diketones with 2-ami-noaiylketones in the presence of catalytic amount of iodine and silica gel at 60 °C under solvent-free conditions Si02 together with molecnlar iodine is a good catalyst and the reaction proceeded well with moderate to high yields. Under this new condition, 1,3-cyclohexanedione reacted faster than other diketones to produce the corresponding quinolines in high yields. 

In 2002, Itoh and Kanemasa found that the combined use of both amine and chiral Lewis acid (R,R)-DBFOX-Ph complex of Ni(II) can be an active catalyst for enantioselective Michael addition of nitromethane or malononitrile to unsaturated carbonyl compounds [37a,b]. Recently, they have reported a new enol ketone synthesis through the reactions between cyclic 1,3-dicarbonyl donors and a,p-unsaturated carbonyl acceptors under the double catalytic activation conditions (10mol% each) of Ni(11)-perchlorate hexahydrate and (2,2,6,6-tetramethylpiperidine (TMP) (114))(Scheme 16.33) [38a,b]. Thus, 1,3-cyclohexanedione (112) is allowed to react with 4-bromo-l-crotonoyl-3,5-dimethylpyrazole (113), in THF at room temperature in the presence of both catalytic amounts to give 4,7,7-trimethyl-3,4,5,6,7,8-hexahy-drobenzopyran-2(H),5-diones (115) in good yields along with high enantioselectivity up to 99% ee. 

Ramin et al. performed the combination of isatin, barbituric acid, and cyclohexane-l,3-dione derivatives in the presence of alum (KAl(S04)2 l2H20) as a catalyst in [BMIM][PF6] to afford spiro[chromeno[2,3-d]pyrimidine-5,3 -indoline]-tetraones 183 after 15 min at 100 °C (Scheme 107). A total of eight types of substituted isatins, two types of 1,3-cyclohexanediones, and three types of barbituric acids were used in this tactic for the library validation. The authors investigated tiie catalytic effect of other Lewis and Bronsted acids such as SSA (silica sulfuric acid), SnCb, p-TSA (para-toluenesulfonic acid), and CAN (ceric ammonium nitrate) under this methodology and foxmd that alum at 10mol% demonstrated significant capability and promotion of reaction rate in [BMIM][PF6] as reaction medium [287]. 

The monomethylation of carbanions derived from 1,3-cyclohexanedione and acetylacetone has been described (eqs 1 and 2) Selective monomethylation of (3-diketones is dependent upon the base employed variable amounts of O-methylation, dimethylation, and carbon-carbon bond cleavage may occur. The tetraethylammonium enolate of p-diketones reportedly provides higher yields of C-methylation without competing side reactions (eq 3). Dimethylation is sometimes a desired reaction pathway. In this case, a large excess of both methyl iodide and base favors the dimethylated product (eq 4). Recently, the combination of a potassium base and a catalytic amount of 18-Crown-6 (eq 5) has been described to provide a higher yield of dimethylation, ... 

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