3-diketone, carbonylation with

The rt,/3-unsaturated linear carbonyl compound 39 is obtained by the decomposition of the cyclic hydroperoxide 38 with PdCl2,[35]. The a, 0-epoxy ketone 40 is isomerized to the /3-diketone 41 with Pd(0) catalyst[36]. The 1,4-epiperoxide 42 is converted into the /3-hydroxy ketone 43 and other products[37]. 

In an asymmetric p-diketone there should be a preference by the enol proton for one of the carbonyls over the other and attempts have been made to determine which it is by C-nmr spectroscopy (Shapet ko et al., 1975 Lazaar and Bauer, 1983). With the additional help of O-nmr spectroscopy it has been possible to demonstrate convincingly that the enol group prefers the carbonyl with a p-group in the following order CF3 > Ph > Bu > Me (Geraldes et al., 1990). 

In the Weiss reaction (Scheme 4), an a-di carbonyl compound (38) condenses with two molecules of dimethyl 3-oxoglutarate (39 E = CC Me) to give a c / s -b icy clo [ 3.3.0 ] o ct-ane-3,7-dione tetraester (40) the one-pot reaction produces considerable complexity, with the sequential formation of four C—C bonds. Simple acid treatment removes the carbomethoxy groups, if desired. While the reaction involves aldol and Michael sequences, the intermediacy of a cyclopentenone [4-hydroxycyclopent-2-enone (41)] has up to now been unproven. A series of such 1 1 adducts has now been reported for a variety of diketones, together with evidence that they are indeed intermediates en route to the bicyclo system.62 Electronic and steric effects on the reaction are also discussed in detail. 

It is also possible to reductively cleave a C-C bond (which is not part of a cyclopropane ring) when this bond is parallel to the system of two adjacent carbonyl groups. The pentacyclic diketone 269 is a perfect example for this stereochemical arrangement and Wenkert and Yoder (75) found that 269 is readily reduced to the tetracyclic diketone 270 with zinc in acetic acid. Paquette and co-workers have reported the transformations 271 272... 

The reaction, of metal carbonyls with 1,3-diketones generally results in a complete displacement of carbon monoxide accompanied by oxidation of the metal to yield 1,3-diketonato complexes. For example, iron pentacarbonyl, chromium hexa-carbonyl, and molybdenum hexacarbonyl afford FefCgHjOOs,1 Cr(CsHr02)8,2 and Mo(CgH702)s,2,s respectively, when allowed to react with 2,4-pentanedione. 

Laurent was the first to react a carbonyl compound, benzil, with an alkali metal. These attempts were more eventful than successful instead of the first radical anion he observed spontaneous ignition [34], Some fifty years later, Beckmann and Paul were more successful, when they reacted aromatic ketones (benzo-phenone) and diketones (benzil) with sodium [35]. They noted the sensitivity of the solutions and of the colored solid products to air and moisture and worked in a hydrogen atmosphere. Although they demonstrated admirable laboratory skills, (cf. Fig. 3), they did not understand the nature of the colored intermediates. 

Thus, quadricylane on treatment with iron carbonyls gave a metallacyclic acyl system 2. ° The product 2, on treatment with oxidants [copper(II) chloride or iron(III) chloride], gave a tetracyclic diketone 3 with a cyclopropane subunit. ... 

These conversions can be applied to organic synthesis in various manners. Thus, quadricyclane can be ring opened and carbonylated with iron carbonyls.Decomplexation of the resulting acyl complex leads to a tetracyclic diketone. 

We can now look at specific examples, and see how the principles above can lead to the aromatic heterocycles. In the first of the two broad categories, where only C-heteroatom bonds need to be formed, and for the synthesis of five-membered heterocycles, precmsors with two carbonyl groups related 1,4 are required, thus 1,4-diketones react with ammonia or primary amines to give 2,5-disubstituted pyrroles two successive heteroatom-to-carbonyl carbon additions and loss of two molecules of water produce the aromatic ring, though the exact order of these several steps is never certain. 

Reagents of type (57) react with simple aldehydes to give expected products, and with aj8-unsaturated ketones to give annelated compounds (Scheme 23).Half-protected a-diketones react with Wittig reagents at the unprotected ketone, and the second carbonyl group can then be deprotected. ... 

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