1.3- dicarbonyl compounds continued

Dicarbonyl compounds continue to attract attention as precursors to unsaturated ketones. Readily prepared trimethylsilyl enol ethers react well with alkyl-lithiums, but poorly with Grignard or dialkylcopper-lithium reagents, to give enones [equation (23)]. a-Oxoketene thioacetals undergo chemoselective... 

TABLE 20. ENOLATES OF g-CYANO CARBONYL AND [3-DICARBONYL COMPOUNDS (Continued)... 

Both A and B are 1,5-dicarbonyl compounds, but only B can be discormected in the usual way. The result is two molecules of an a,p-unsaturated ketone and we can continue the analysis ... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

The self-condensation of 1,3-dicarbonyl compounds provides a useful route to 4-hydroxy-pyran-2-ones and is catalyzed by acids or bases. Alcohol is continuously removed during the reaction. Amongst a number of examples, mention can be made of the detailed procedure for the synthesis of 3-acetyl-4-hydroxy-6-methylpyran-2-one (dehydroacetic acid) (550SC(3)23l) and the formation of the cyclopentyl derivative (321) (64RTC39). Deacylation at C-3 can generally be achieved on heating with acid. 

Following the production of 1,2-enol forms of aldose and ketose amines, a series of degradations and condensations results in the formation of melanoidins. The a-fi-dicarbonyl compounds enter into aldol type condensations, which lead to the formation of polymers, initially of small size, highly hydrated, and in colloidal form. These initial products of condensation are fluorescent, and continuation of the reaction results in the formation of the brown melanoidins. These polymers are of nondistinct composition and contain... 

The use of a-dicarbonyl compounds with ammonia and an aldehyde continues as a common synthetic method. " Thus a series of 2-aryl-5-trifluoromethyl-4-phenylimidazoles (2) have been prepared from the previously unknown 3,3,3-trifluoro-l-phenylpropane-l,2-dione monohydrate (1) as shown in Eq. (1). As an extension of earlier studies of imidazole formation by the action of ammonia on reducing oligosaccharides, Richards ... 

The reactions of amidines or guanidines with a-functionalized carbonyl compounds continue to be utilized for the synthesis of imidazoles. Thus, the mixed anhydride of acetic and chloroacetic acids reacts with symmetrical diarylguanidines to give l-aryl-2-arylaminoimidazolin-4-ones, and there is competitive formation of imidazoles and pyrimidines in the reaction of benzamidine with 3-bromobenzo-4-pyrones (18). Imidazoles are minor products, but are favored in nonpolar solvents. The use of a-dicarbonyl compounds with guanidine gives 2-amino-4-hydroxy-4-methyl-4//-imid-azoles, which give excellent yields of 2-aminoimidazoles on catalytic hydrogenation. " ... 

Heating a 1,2-dicarbonyl compound with an o-phenylenediamine continues to be used and varied for the preparation of quinoxalines. 1,2,3-Propanetrione... 

Continuing studies on the application of organic phosphorus and sulfur compounds for the synthesis of 1,4-dicarbonyl compounds and functionalized cyclopentenones, Mikolajczyk and Zatorski [17] developed a short and efficient synthesis of methylenomycin B starting from and y-ketophosphonates 2 and 3. These two reagents were revealed by retro synthetic analysis shown in Scheme 1. 

The manganese(III) species A should be reproduced in the reaction system, and the catalytic cycle must be continued until the added alkenes and 1,3-dicarbonyl compounds are completely consumed [46,77,79,80,83,106, 125-128,134,135,142,143]. The mechanism for the formation of peroxides is summarized in Scheme 31. 

P-Dicarbonyl compounds can be converted to the corresponding fluorinated compounds in formic acid using 10% F2 in N2 in a microflow system by continuous... 

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