Esters acid cyclic

A variety of cyclic ortho esters,including cyclic orthoformates, have been developed to protect czs-1,2-diols. Cyclic ortho esters are more readily cleaved by acidic hydrolysis (e.g., by a phosphate buffer, pH 4.5-7.5, or by 0.005-0.05 M HCl) than are acetonides. Careful hydrolysis or reduction can be used to prepare selectively monoprotected diol derivatives. 

Monobasic carboxylic acids with an a-methyl group Esters of aliphatic dibasic carboxylic acids Cyclic sulfides... 

The scope of this reaction is similar to that of 10-21. Though anhydrides are somewhat less reactive than acyl halides, they are often used to prepare carboxylic esters. Acids, Lewis acids, and bases are often used as catalysts—most often, pyridine. Catalysis by pyridine is of the nucleophilic type (see 10-9). 4-(A,A-Dimethylamino)pyridine is a better catalyst than pyridine and can be used in cases where pyridine fails. " Nonbasic catalysts are cobalt(II) chloride " and TaCls—Si02. " Formic anhydride is not a stable compound but esters of formic acid can be prepared by treating alcohols " or phenols " with acetic-formic anhydride. Cyclic anhydrides give monoesterified dicarboxylic acids, for example,... 

A substituted acetamidomalonic ester, tetraethyl 1 -acetamido-4-hydroxy-butane-l,l,3,3-tetracarboxylate, was used in the preparation of cis- and frans-pyrrolidine-2,4-dicarboxylic acids, cyclic analogs of glutamic acid (91TL3049). 

Meldrum s acid Malonic acid, cyclic isopropylidene ester (8) 1,3-Dioxane-4,6-dione, 2,2-dimethyl- (9) (2033-24-1)... 

From the presence of uronic acid, sulfate half-ester, pyruvyl cyclic acetal, or succinate half-ester groups. 

Cycloaliphatic Epoxy Resins. This family of aliphatic, low viscosity epoxy resins consists of iwo principal varieties, cyclouleliils epoxidi/.cd with peracetic acid anil diglvcidyl esters of cyclic diearboxvlic acids. 

JOC 47 2820 (1982) (/1-diketones to hydroxy ketones) 50 127 (fi-keto carboxylate), 3411 (fi-diketones to hydroxy ketones) (1985) 51 1253 (2,2-dithioalkan-l-ones), 2795 (a-flooro ketones) (1986) 52192 (fi-keto esters), 256,1141,1359 (fi-keto esters), 2036 (/1-diketones to hydroxy ketones), 2086 (a-acetoxy ketone), 2244 (fi-keto ester), 3223 (cyclic /1-diketones to hydroxy ketones), 4363 (y- arid 5-keto acids) (1987) 53 860, 1969, 2589 (x-keto ester), 4405 (a-acyloxy ketone), 4962 (1988) 54 2238 (/S-diketone to fi-hydroxy ketone), 2274, 3221 (a-diketone to a-hydroxy ketone) (1989) 55 3917 (1990)... 

Dimethyl-1,3-Dioxane-4,6-dione (Meldrum s Acid) Malonic acid, cyclic isopropylidene ester (8) 1,3-Dioxane-4,6-dione, 2,2-dimethyl- (9) (2033-24-1) Ethylenediammonium diacetate 1,2-Ethanediamine diacetate (9) (38734-69-9) (R)-Citronellal 6-Octenal, 3,7-dimethyl-, (R)-(+)- (8,9) (2385-77-5)... 

The Baeyer-Villiger Oxidation is the oxidative cleavage of a carbon-carbon bond adjacent to a carbonyl, which converts ketones to esters and cyclic ketones to lactones. The Baeyer-Villiger can be carried out with peracids, such as MCBPA, or with hydrogen peroxide and a Lewis acid. 

CARBONIC ACID, CYCLIC 1 -(HYDROXYMETHYL)-2-METHYLETKYLENE ESTER, ESTER With 6-(2-AMIN0-2-PHENYLACETAMID0)-3,3-DIMETHYL-7-OXO-[Pg.228]

To 5.69 g of this acetal in 410 ml of t-butanol and 11 ml of water was added a mixture of 5.80 g of potassium carbonate, 22,8 g of sodium periodate, and 270 mg of potassium permanganate in 1230 ml of water. The reaction mixture was stirred at 20-25°C for 20 hours and concentrated in vacuo to remove t-butanol. Ethylene glycole (0.5 ml) was added and reaction mixture extracted with 1 1 ether-benzene to remove neutral material. The aqueous layer acidified with solid sodium dihydrogen phosphate and extracted 4 times with 1 1 ethyl acetate-benzene. The organic layer was dried over sodium sulfate and evaporated to dryness in vacuo affording (+/-)-3-acetyl-2a-(2-carboxyethyl)-5-oxo-ip-cyclopentaneheptanoic acid methyl ester, 5-cyclic ethylene acetal as a mixture of the 3a and 3p isomers. 

The reaction 4.25 g of (+/-)-3p-acetoxy-2a-(2-methoxycarbonylethyl)-5-oxo-ip-cyclopentaneheptanoic acid methyl ester, 5-cyclic ethylene acetal in 25 ml of methanol with 6 ml of 1.00 N sodium methoxide under nitrogen at room temperature for 2 hours produced pure (+/-)-2a-(2-methoxycarbonylethyl)-3p-hydroxy-5-oxo-ip-cyclopentaneheptanoic acid methyl ester, 5-cyclic ethylene acetal after chromatographical purification with silica gel (eluent 25% acetone in chloroform). 

The above product was dissolved in 7.5 ml of methanol and 60 mg of ethylenediamine in 5 ml of methanol was added dropwise at 0°C and the mixture stirred for 45 min at 20°C. And the solvent evaporated in vacuo. The residue was chromatographed on 35 g silica gel eluting with 30% acetone and chloroform taking 40 fractions of 4 ml each. Fraction 5-14 was evaporated to dryness in vacuo affording 250 mg (+/-)-3p-hydroxy-2a-(3-oxo-l-octenyl)-5-oxo-ip-cyclopentaneheptanoic acid methyl ester, 5-cyclic ethylene acetal, Xmax (methanol, 232 nm, E 12500). 

MELDRUM S ACID 2,2-DIMETHYL-1,3-DIOXANE-4,6-DIONE MALONIC ACID, CYCLIC ISOPROPYLIDENE ESTER 1,3-DIOXANE-4,6-DIONE, 2,2-DIMETHYL- (2033-24-1), 67, 170 69, 33 p-Mentha-6,8-dien-2-one (6485-40-1), 66, 13... 

Polymerization of cyclic esters of phosphoric acid (cyclic phosphates) is interesting from the synthetic point of view, because the resulting polymers have the sequence of atoms of the chain identical with this, which appears in important biopolymers such as nucleic or teichoic acids. Both 5- and 6-membered cyclic phosphates undergo polymerization. 

Monosubshtuted hydantoins are a-amino acids cyclically protected at both the carboxyl- and the a-amino group. They can be easily prepared from an aldehyde and isocyanate or by the Bucherer-Bergs synthesis and similar methods. Indeed, the hydantoin synthesis is also a prachcal method for the preparahon of the racemic amino acid. Enzymes belonging to the dihydro-pyrimidinase family hydrolyze hydantoins to the carbamoyl amino acid. The latter can be hydrolyzed in turn to the amino acid by a second enzyme, a carbamoylase. Both enzymes can discriminate between enantiomers and, if their action is cooperative, either the L- or the D-amino acid can be obtained (Scheme 13.10) [36]. What makes the system of special interest is that the proton in the 5-position of the hydantoin ring (it will become the a-hydrogen in the a-amino acid) is considerably more acidic than conventional protons in amino acid esters or amides and much more acidic than the amino acid itself. Thus, the hydantoin can be often racemized in situ at slightly basic pH where the enzymes are stiU stable and active. If these condihons are met. 

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