Meldrum’s acid. See

Acetyl Meldrum s acid See 5-(1-hydroxyethylidene)-1,3-dioxane-4,6-dione... 

One route to o-nitrobenzyl ketones is by acylation of carbon nucleophiles by o-nitrophenylacetyl chloride. This reaction has been applied to such nucleophiles as diethyl malonatc[l], methyl acetoacetate[2], Meldrum s acid[3] and enamines[4]. The procedure given below for ethyl indole-2-acetate is a good example of this methodology. Acylation of u-nitrobenzyl anions, as illustrated by the reaction with diethyl oxalate in the classic Reissert procedure for preparing indolc-2-carboxylate esters[5], is another route to o-nitrobenzyl ketones. The o-nitrophenyl enamines generated in the first step of the Leimgruber-Batcho synthesis (see Section 2.1) are also potential substrates for C-acylation[6,7], Deformylation and reduction leads to 2-sub-stituted indoles. 

Cyclic lactim ethers (465, n = 0 and 1, R2 = see below, R5 = OMe) were condensed with Meldrum s acid (421) in the presence of a catalytic... 

Chances may be better, however, when a cyclic starting material includes the acyl group R4—CO. Here, the pathway based on Meldrum s acid was proven very useful [87JCS(P1)1177, 87TH1]. De Shong et al. started with R4-substituted isoxazoles (83JOC1149). The isoxazolium salts, obtained from ethyl bromoacetate, convert into /3-ketoamides, where best results were observed in two-phase systems. These /3-ketoamides cyclized to 3-acyI-tetramic acids by adding base. (See Fig. 13.)... 

An attempt to react 2b with ethyl chloroformate in the presence of pyridine, the Einhorn reaction, gave 73 in low yield and other unknown products. The expected 3-ethoxycarbonyltetramic acid was not isolated (91UP1). An analogous reaction is described for Meldrum s acid (92LA813) (See Fig. 34.)... 

Ozonolysis of diketene affords formaldehyde [50-00-0] and the very un-stable malonic anhydride [15159-48-5] (114), which readily decomposes to C02 and ketene, but can be converted at low temperature to malonic acid monoesters or Meldrum s acid (115) (see Malonic acid AND DERIVATIVES). 

Many modifications of this basic chemistry have been explored to tailor these resists to deep-UV radiation. For example, changes have been made in the sensitizer so that it bleaches in this wavelength region. Early work in this area was performed on diazo-Meldrum s acid (54) (see structure). This compound functioned as a deep-UV-bleachable dissolution inhibitor however, it was somewhat volatile and, consequently, could be depleted via evaporation during soft bake. More-recent studies have therefore focused on less-volatile sensitizers incorporating heteroatom substitution (55) and on increases in molecular weight (56). 

For the reaction of 5-acyl Meldrum s acid with allylic alcohols, see Y. Oikawa, K. Sugano and O. Yonemitsu, J. Org. Chem., 1978, 43, 2087. 

Malonomonoamides can be condensed with aldehydes to give acrylamides or cinnanamides, but condensation with malonodiamides is of only minor impjortance. In contrast to Meldrum s acid (58), Knoevenagel reactions of barbituric acid (56) and A A -dimethylbarbituric acid have been less explored. However, several aliphatic, aromatic and heteroaromatic aldehydes are known to react easily and with high yields in most cases. Reactions of 1,2-dimethyl-3,5-pyrazolidinedione (93) with several aliphatic and aromatic aldehydes using standard conditions yield Knoevenagel products in good yield. A similar reactivity is observed with 2-phenyl-3,5-dioxoisoxazolidine (94) and oxazepanediones (45 see Section 1.11.2.5). Recently, the oxidations of alcohols to carbonyl compxiunds and thiols to disulfides with 5-arylidene-l,3-dimethylbarbituric acids (95) have been described Mechanistically (95) mimics enzymic oxidation by flavin adenine dinucletide (FAD). ... 

It is known that acyl Meldrum s acids are not always stable. For example, see Reference 8b. 

Pyranoid Compounds.-Reaction of 2,3,4,6-tetra-O-acetyl-D-glucose with the active methylene compound Meldrum s acid gives the C-glycoside 98 in 59% yield on acid-catalysed hydrolysis this affords the acetic acid derivative 99. The same condensation reaction applied to L-arabinose and o-mannose gives furanosyl compounds directly (see next section). 3-Linked glycosyl acetic acids 100,101 are produced on treatment of... 

Thioacylketenes are only stable at very low temperatures and even at -196 °C only thietons, their rearrangement products, can be detected by infrared spectroscopy (band at 1790 cm ). a-Imidoylketenes are obtained by flash vacuum pyrolysis of Meldrum s acid derivatives, but only an oxoketenimine (band at 2076 cm ) rearrangement product is detected at -77 K . Also, the unstable methyleneketenes (R2C=C=C=0) are obtained from suitable precursors. In the absence of trapping agents their cyclodimers are isolated (see Section 4.1.2). 

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