1,3-dicarbonyl systems

FINALS, which perform disconnections only if none of the above algorithms could be applied. This usually happens if only one functional group not included in group 2 is present for instance, hydration of an isolated double bond. However, the consonant 1,3-dicarbonyl systems are also included in this group... 

As shown, the disconnection of the consonant 1,3-dicarbonyl system present in 1 would lead to the precursor 2, the acylation of which would present problems of regioselectivity. However, disconnection of the alkyl group at the a-position of the carbonyl groups leads to precursor 3, the alkylation of which would not present any problem of regioselectivity. 

In phenylbutazone (86a) and sulfinpyrazone (86b) the acidity of the hydrogen on the methylene carbon of the 1,3-dicarbonyl system facilitates nucleophilic attack at C-l of the glucuronic acid moiety of UDPGA (see Scheme 7). The glucuronides formed (87a, 87b)... 

Alternatively, an anion stabilizing group alpha to the carbonyl group of the cyclo-butanone provides a pathway for cleavage by attack of a nucleophile on the cyclo-butanone carbonyl carbon. C-Acylation creates the familiar 1,3-dicarbonyl system which, by deacylation involving attack at the cyclobutanone carbonyl group, leads to a geminal alkylation as shown in Eq. 115 b 47,79). 

Lactone 5 can be obtained in both enantiomeric forms or as a racemate according to the described procedure. The reaction sequence includes the in situ formation of an alkylidene-1,3-dicarbonyl system 7 which can act as a heterodiene in an intramolecular hetero-Diels-Alder addition. A small amount of the ene product 4 with de > 98% is formed at room temperature as well. The remarkable selectivity in formation of diastereomer 3 is explained by an energetically more favorable exo transition state 8 with a pseudo-chair arrangement having the methyl group quasi-equatorial. Polycyclic cis-fused compounds can also be synthesized by the procedure above,9 and a related sequence to the cannabinoid skeleton has been described using appropriate 1,3-dicarbonyl reactants.10... 

D. J. Ager, S. A. Laneman, Reductions of 1,3-Dicarbonyl Systems with Ruthenium-Biarylbisphosphine Catalysts, Tetrahedron Asymmetry 1997, 8, 3327-3355. 

The enol is stable it is delocalized. We can show the delocalization and explain why vitamin C is called ascorbic acid at the same time. The black enol proton is acidic because the anion is delocalized over the 1,3-dicarbonyl system. 

Ager DJ, Laneman SA. Reduction of 1,3-dicarbonyl systems with ruthenium-biarylphosphine catalysts. Tetrahedron Asymmetry 1997 8 3327-3355. 

Deacylation. A-Acyloxazolidinones can be cleaved by EtSK. Thioester that is part of a 1,3-dicarbonyl system undergoes C-C bond cleavage on exposure to AgN03-2,6-lutidine in aqueous THF. 

In 2004, Jorgensen and coworkers disclosed a-hydroxylation of 1,3-dicarbonyl systems 104 (Scheme 6.31) [59]. They used hydroquinine (106) as the organocatalyst and cumyl hydroperoxide as the oxidant for the enantioselective a-hydroxylation of various P-keto esters 104 with enantioselectivities up to 80% ee. Optimization studies revealed that the 0(9)-OH group of 106 is critical for good stereoselectivity, and the best enantioselectivity was obtained under CH2Br2 solvent at room temperature. 

When the position between two carbonyl groups is blocked, attack by a nucleophile 31 occurs at the more electrophilic of the two (an aldehyde if there is one) cleaving 32 the 1,3-dicarbonyl system. 

Oxazolidines 30 and oxazinanes 31, depending upon the nature of their C-2 substituents, could react with 1,3-dicarbonyl systems which have considerable enolic tautomer components in 1 2 or 1 1 stoichiometry in a manner analogous to their reactions with enamines to form oxygen isosteres of pyridine derivatives (96T14273). 

The acetyl group in the 1,3-dicarbonyl system shown was removed by hydrolysing with 10% aqueous sodium carbonate during 2 hours giving the parent pyranobenzochromenone, 2,2,8-trimethyl-3,4-dihydro-2H,3H-benzo- [1,2-b 5,4-bl-dipyran-6-one in 55% yield (ref.126). 

Isoxazoles have a considerable synthetic potential because of their ring-opening reactions as masked 1,3-dicarbonyl systems [84]. 

Chromones and flavones show analogies in their reactions to 4i/-pyran-4-one, i.e. they behave as masked 1,3-dicarbonyl systems. Protonation and alkylation occur on oxygen. Electrophilic attack takes place at the deactivated pyran-4-one ring in the 3-position, e.g. aminomethylation can be brought about under Mannich conditions. 

Brands and DiMichele reported the intramolecular Michael cychzation of a 1,3-dicarbonyl system (190) to alkynyl ester. The resulting double bond was hydrogenated stereoselectively to give an AC ring system (189) [97] (Scheme 16). Subsequent intramolecular aldol-type cyclization of 188 furnished a suitably substituted ABC tricychc intermediate (187). Using the same strategy, Fiirstner and coworkers synthesized an ACD tricychc intermediate (191) [98]. 

Complementary approaches to mono protected 1,3-dicarbonyl systems in which either the starting or the introduced carbonyl is protected, have been reported. Thus ketone formylation with Vilsmeyer s reagent followed by treatment with ethylene glycol... 

This MCR domino process involves initial CFsCOOH-promoted propargylation of the 1,3-dicarbonyl system and subsequent condensation between the resulting y-ketoalkyne 89 and the primary amine to afford the propargylated P-enaminoester 90, which undergoes an Ru-catalyzed 5-exo-dig aimulation to form the cyclic enamine 91, finally tautomerizing to the pyrrole 88. 

Thus, a logical retroanalytical route (I, FGA a disconnection b—> FGI c) leads via 6 and monooxime 8 to 1,3-dicarbonyl systems and hydroxylamine as potential educts for isoxazole synthesis. 

First, cyclohexanone is alkylated by 32 giving rise to the masked triketone 33. On catalytic hydrogenation of 33, the isoxazole ring is reductively opened to give the enaminone 34, which cyclizes in situ to the enamine 35. On treatment with aqueous NaOH, 34 is converted to the 1,5-dione 36 (by enamine hydrolysis and acid cleavage of the 1,3-dicarbonyl system of the triketone intermediate), which undergoes base-induced intramolecular aldol condensation to the bicycloenone 37 (in analogy to a Robinson annulation) [317] ... 

Chromones differ from coumarins (vc=o 1710 cm ) by the position of the C=0 absorption band in the IR (vc=o 1660 cm ). Chromones, especially flavones, are characterized by two UV absorption bands in the region of 240-285 and 300-400 nm. Chromones and flavones show analogies to 4H-pyran-4-one in their reactivity, that is, they behave as masked 1,3-dicarbonyl systems. 

Copper(ll) acetate performs a double role activation of the triacyl methane group by coordination and production of the reactive triacylmethyl radical by a coupled redox reaction. The proposed mechanism is supported by the fact that 274 is present in the auto-oxidation reaction mixture of hexahydrocolupulone, while compounds 275-279 are absent. Auto-oxidation occurs indeed at the ring carbon atom C-4 (see 13.1.2.). The radicals are in this case produced within the 1,3-dicarbonyl system in the ring, whereby only 274 can be formed in an analogous way as described before (pathway B). 

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