Acids Meldrum

Thermal fragmentation of l,3-dioxin-4-ones or acylated Meldrum acids with generation of a-oxoketenes, hetero Diels-Alder reactions of the latter, and their transformations into lactones and lactams, among them macrocyclic 99YGK76. 

MCRs of Hantzsch and Biginelli-types with participation of aldehydes, aminoa-zoles, and cyclic CH-acids, first of all 1,3-diketones and Meldrum acid, as well as the treatments discussed in the previous sub-chapter, are in the focus of interest due to high biological activity of their products. However, on the other hand, in many cases these processes can give several final heterocycles with different position or regiodirection. Moreover, sometimes for the same reactions carried out under similar conditions contradictory facts were published with high level of credibility. 

Numerous solvent-free Knoevenagel condensations with malononitrile, methylcyanoacetate, dimedone (255), and Meldrum acid proceeded with high to quantitative results with intermediate melt or full melt at higher temperatures but with direct crystallization [107]. 

FVP of the Meldrum acid derivatives 347 gave the 2-substituted l,3-oxazin-6-ones 348 (Scheme 64). This method proved to be an effective procedure for the preparation of both 2-aryl- and 2-alkyl-substituted derivatives. The yields were not significantly influenced by the increasing bulkiness of the alkyl groups R <1996T3163>. 

Several attempts have been made to redesign the traditional two-component near-UV positive resist systems to make them compatible with the deep-UV. Recall that the major problems associated with deep-UV exposure of conventional resists are related to non-bleaching of the o-quinonediazide sensitizer on exposure because of photoproduct absorbance, and strong absorption of the novolac resin. Willson and coworkers34 attempted to solve this problem using dissolution inhibitors based on 5-diazo Meldrums acid, which undergoes photochemical decomposition as follows ... 

Meldrum acid 2 (288 mg, 2.00 mmol) and aldehyde 1 (2.00 mmol) were coground and heated to 50 °C when 3a, b crystallized after intermediate melting. The quantitatively obtained pure product 3a, b was dried at 80 °C in a vacuum. Mp 193 °C and 162 °C. 

Complexes of unsymmetrically substituted conjugated dienes are chiral. Racemic planar chiral complexes are separated into their enantiomers 84 and 85 by chiral HPLC on commercially available /f-cyclodextrin columns and used for enantioseletive synthesis [25]. Kinetic resolution was observed during the reaction of the meso-type complex 86 with the optically pure allylboronate 87 [26], The (2R) isomer reacted much faster with 87 to give the diastereomer 88 with 98% ee. The complex 88 was converted to 89 by the reaction of meldrum acid. Stereoselective Michael addition of vinylmagnesium bromide to 89 from the opposite side of the coordinated Fe afforded 90, which was converted to 91 by acetylation of the 8-OH group and displacement with EtjAl. Finally, asymmetric synthesis of the partial structure 92 of ikarugamycin was achieved [27],... 

The Meldrum acid-adducts reacted with bromine in dichloromethane to produce the Te, Te-dibromides2. 

Condensation of complex 9 with Meldrums acid (10) gives complex 11 in good yield, which is then reacted with an excess of vinyl-MgBr to afford complex 12. The complete diastereoselec-tivity of the latter reaction can be explained by assuming that the substrate prefers conformation 14 shown in Fig. 2 and that the nucleophile attacks the ligand exclusively from the less hindered TT-face opposite to the Fe(CO)3. 

Other Meldrum acid condensation reactions are provided (1). 

The experimental evalution of acute toxicity of germyl(silyl)-substituted furfurylidene Meldrum acid (Table 5) has demonstrated that the introduction of the trimethylgermyl group lowers the toxicity of the compound by ca 4 times. On the other hand, the introduction of the trimethysilyl group does not change significantly the toxicity of the unsubstituted derivative. The carbon analogue is the most toxic derivative in this series of compounds . 

Flash vacuum pyrrolysis of Meldrum acid, pyrrol-3(2 //)-ones, thiophen-3(2 H)-ones, azepin-3(2 F/)-ones, and pyrrolizin-3-ones 04ACA19. 

The synthetically important isopropylidene malonates (Meldrum acids) can be prepared in a one-pot procednre employing this method. 

Meldrum acid, synthesis, physical properties, reactivity of 78CSR345. 

A different approach can be found in the reaction of diketene 44 with Meldrum acid (45). Treatment of the resulting derivative 46 with TsOH in benzene forms 3-carboxy-4-hydroxy-6-methyl-2-pyrone (47) (84SC265). 

Different reaction patterns are manifested when Meldrum acid that is substituted with a cinnamyl ester is exposed to (Ph3P)4Pd and a mixture of (PhCN)2PdCl2-Yb(OTf)3. 

Synthetic applications of the pyrolysis of Meldrum acid derivatives 01S2059. 

If the scale applies to another highly activated system, benzylidene-Meldrum acid, 12, then the slope calculated for the pair of nucleophiles PhO- and OH- is higher than unity, because log (k hoJkOH ) = 1-39 whereas AN+ = 0.85, but the scale is lower than unity when calculated for the OH--N20 and PhO--H20 pairs (24). 

Intramolecular Friedel-Crafts acylation of enolizable benzyl Meldrum acids 22 wifh scandium triflate (7%-12% mol) in refluxing nitromethane or acetonitrile is a powerful tool for the preparation of a variety of indan-l-ones 23 (Table Meldrum acid derivatives, mono- and dis-... 

The reaction can also be extended to quatemized benzyl Meldrum acids 24, affording products 25 with a different substitution on the cyclo-pentanone ring (Table 3.10). The method is also applied to the synthesis of... 

Suitable condensing agents for this reaction are acetic anhydride,259,260 hydrogen chloride and thionyl chloride,261 dicyclohexylcarbodiimide,262 and phosphorus pentaoxide.263 For example, barbituric acids, 2-hydroxy-1,4-naphthoquinone, and methylene di(phenyl sulfone),259 malonodinitrile,261 Meldrum acid and 2,3-indenedione,262 dinitromethane and dihydroresorcinol260 yield ylides by this method. 

Acid 20 has been transformed to the acid chloride 21 which has been condensed with Meldrums acid to give, after solvolysis with methanol, the p-keto ester 22. Subsequent treatment with / -tosylazide gave the diazo compound 23 which has been stereoselectively cyclized to 2-carbomethoxy-tricyclo[3.3.0.0]octan-3-one 24 with copper acetylacetonate as catalyst. 

The Meldrum acid condensate with 3-formyl-2,4,7-trimethylbenzofuran namely... 

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