1,3-Dicarbonyl type compounds

Reaction of an enolate, generated from a P-keto ester or other 1,3-dicarbonyl-type compound with an aldehyde or ketone is known as the Knoevenagel condensation... 

The product from the addition of an enolate of a 1,3-dicarbonyl-type compound with an aldehyde (or ketone) dehydrates readily to give the a,(3-unsaturated dicarbonyl product. This is known as the Knoevenagel condensation reaction, typically carried out under mild conditions with an amine base, and is a useful method for the formation of alkenes bearing electron-withdrawing substituents (see Section 1.1.3). 

Several 9-substituted tetrahydroxanthen-l-ones result from the asymmetric Bronsted acid-catalyzed addition of the in situ generated o-qui-none methides from hydroxyarylbenzyl alcohol derivatives, and their subsequent reaction with cyclohexane-1,3-diones (Scheme 71) (14AGE13258). Other examples arise from a one-pot three-component reaction of salicylaldehydes, cyclic 1,3-dicarbonyl compounds and thiols, in the presence of ammonium chloride in aqueous medium at room temperature (14S73). A one-pot pseudo-three-component reaction of arylg-lyoxals and 2-thiobarbituric acid gives 9-aroyl tetrahydroxanthene-type compounds (14AJC283). 

Conventional synthetic schemes to produce 1,6-disubstituted products, e.g. reaction of a - with d -synthons, are largely unsuccessful. An exception is the following reaction, which provides a useful alternative when Michael type additions fail, e. g., at angular or other tertiary carbon atoms. In such cases the addition of allylsilanes catalyzed by titanium tetrachloride, the Sakurai reaction, is most appropriate (A. Hosomi, 1977). Isomerization of the double bond with bis(benzonitrile-N)dichloropalladium gives the y-double bond in excellent yield. Subsequent ozonolysis provides a pathway to 1,4-dicarbonyl compounds. Thus 1,6-, 1,5- and 1,4-difunctional compounds are accessible by this reaction. 

This type of synthesis has been used extensively in the preparation of hydroxamic acids resembling aspergillic acid. a-Aminohj droxamic acids react with a-dicarbonyl compounds to yield pyrazine hydroxamic acids (18). Glyoxal and diacetyl react readily, but poor... 

The reaction of 3-amino-4-cyanofurazan with (3-dicarbonyl compounds in the presence of catalytic amounts of nickel acetylacetonate (Ni(acac)2) gave labile enamines that on treatment with acetic acid afforded fused pyridines of type 100 in 80-95% total yields (Scheme 51) (94MC57). Eurther syntheses of furazano-pyridines can be found in the review by Sheremetev (99RCR137, 99UK154). 

Ultraviolet and infrared spectroscopy indicate that quinoxaline-2,3-dione type structures are preferred to tlie tautomeric 3-hydroxy-quinoxalin-2 One or 2,3-dihydroxyquinoxaline forms. The light absorption properties (UV) of quinoxaline-2,3-dione have been compared with those of its NN -, ON-, and OO -dimethyl derivatives (79, 80, and 81), and also its N- and 0-monomethyl derivatives (43 and 82). The parent dicarbonyl compound and its mono- and di-A -methyl derivatives show very strong carbonyl absorption near to 1690 cm split into two peaks. 

The major developments of catalytic enantioselective cycloaddition reactions of carbonyl compounds with conjugated dienes have been presented. A variety of chiral catalysts is available for the different types of carbonyl compound. For unactivated aldehydes chiral catalysts such as BINOL-aluminum(III), BINOL-tita-nium(IV), acyloxylborane(III), and tridentate Schiff base chromium(III) complexes can catalyze highly diastereo- and enantioselective cycloaddition reactions. The mechanism of these reactions can be a stepwise pathway via a Mukaiyama aldol intermediate or a concerted mechanism. For a-dicarbonyl compounds, which can coordinate to the chiral catalyst in a bidentate fashion, the chiral BOX-copper(II)... 

Thiophenes of type 31 (X-Y = CH) were generated via Lawesson s reagent-mediated cyclization of 1,4-dicarbonyl compounds 30 under microwave irradiation in the absence of solvent [37]. The reaction was carried by mixing the two solid reagents in a glass tube inserted inside a household microwave apparatus and irradiating until the evolution of H2S ceased. An interesting application of this method is the preparation of liquid crystals and other ferro- and antiferroelectric material such as compound 33 (Scheme 10). 

Selenium dioxide can be used to oxidize ketones and aldehydes to a-dicarbonyl compounds. The reaction often gives high yields of products when there is a single type of CH2 group adjacent to the carbonyl group. In unsymmetrical ketones, oxidation usually occurs at the CH2 that is most readily enolized.255... 

A further type of rearrangement occurs in 1,3-dicarbonyl compounds/48 ... 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

---