Lead acid diester

Glycol cleavages with Pb(OAc)4 preferentially proceed via five-membered lead(IV) acid diesters. Such esters are shown in Figure 17.24 as C and D. Each one of these esters decomposes in a one-step reaction to furnish Pb(OAc)2 and two equivalents of the carbonyl compound. The cleavage is caused by the concerted shift of three valence electron pairs. One of these becomes a lone pair at Pb. The oxidation number of lead is thereby reduced from +4 to +2. 

Asymmetrization of a prochiral dicarboxylic acid diester catalyzed by lipases, where the stereo center of the product is located on the acyl side, becomes a single-step process because the polar carboxylic acid and/or amide formed are not well accepted as substrates by the Upase. One example is the enantioselective hydrolysis or ammonolysis of diethyl 3-hydroxyglutarate, as shown in Scheme 7.4, a reaction which leads to the formation of a precursor for the important chiral side chain of atorvastatin, lipitor [40, 41]. The S-enantiomer was formed with high e.e. (98%), but unfortunately this is the undesired enantiomer for the production of the pharmaceutically important product. Only a-chymotrypsin gave a predominance of the... 

Polyamic acid methacrylate esters are the first self-patternable, pure organic polyimide precursors to be described. They are the polymer basis of the first technically applied resist to produce polyimide patterns in a direct process. They are synthesized simply by the addition of hydroxyethylmethacrylate to aromatic acid dianhydride, and subsequent polycondensation of the intermediate tetracarboxylic acid diester with aromatic diamines. These polyimide precursors give rise to a number of special photoresist properties which lead to important applications, such as photolithographically produced protection layer against a-radiation on memory... 

Starch, when stirred with concentrated sulfuric acid, is degraded and at the same time esterified " to form sulfuric esters capable of yielding insoluble lead, calcium, and barium salts. Degradation of the starch is decreased if it is added slowly and with stirring to a warm mixture of dry pyridine, chlorosulfuric acid, and anhydrous chloroform. After two hours, a product may be recovered by precipitation and washing in dry methanol. In this way, Tamba has isolated a sulfuric acid diester of starch. The sulfuric acid esters are unstable in aqueous solutions and hydrolyze readily with the liberation of sulfuric acid. 

Anodic decarboxylative methoxylation has also been used to generate an efficient electrophilic chiral glycine equivalent. This is produced from the cyclic dipeptide of L-proline and aminomalonic acid diester. Anodic decarboxylation of the remaining carboxylic function leads to the chiral iV,<9-acetal, which can undergo nucleophilic substitution followed by hydrolysis to give back L-proline and the nonproteinogenic new enantiopure i)-amino acid [Eq. (49)] [201]. 

Aqueous dispersion of a triple-chain glutamic acid diester monoamide shows beautiful helical fibers under the light microscope, which slowly close to form tubules. Above 50°C the fibers melt and rearrange to vesicles. Twisted ribbons made of similar molecules with azobenzene in the hydrophobic core polymerize upon UV irradiation. This leads to the disappearance of an induced CD spectrum of surface adsorbed methyl orange. Alanine-derived amphiphiles with azobenzene units in the chain also form helical fibers in water. They absorb at 350 run when the number of the methylene groups in the outer chain is even and at 320 nm when odd. The chromophore in the fiber is presumably less stacked in even-numbered alkyl chain assemblies (Fig. 9.5.i). 

Hydroxyethyl esters can be prepared from the free acid by reaction with ethylene carbonate. During an attempt to protect the ketone group of a keto-acid by 1,3-dioxolane formation, it has been found that mixed carboxylate sulphonate esters [e.g. (121) from ethylene glycol and tosic acid] can easily be formed extensions of this reaction show it to have a general applicability. In the presence of fluoride ions, carboxylic acids become sufficiently nucleophilic to attack alkyl halides. Thus, reaction between an acid and 1,3-dibromopropane leads to diesters (122). Molecular sieves have been recommended as suitable absorbants... 

The aza-Petasis-Ferrier rearrangement is not a true concerted sigmatropic reaction, since it is thought to proceed via C-O bond cleavage of a hemiaminal vinyl ether by the action of an acid catalyst to afford a reactive iminium cation and the enol form of an aldehyde these two intermediates combine subsequently in a Mannich-type process, leading to 3-amino aldehydes (Scheme 40.45) [54]. Recently, Terada and Toda used a BINOL-derived phosphoric acid diester as a catalyst for this interesting reaction [55]. 

The reactions are catalyzed by tertiary amines, quaternary ammonium salts, metal salts, and basic ion-exchange resins. The products are difficult to purify and generally contain low concentrations of acryhc acid and some diester which should be kept to a minimum since its presence leads to product instabihty and to polymer cross-linking. 

Fig. 2. Synthesis of uma2enil (18). The isonitrosoacetanihde is synthesized from 4-f1iioroani1ine. Cyclization using sulfuric acid is followed by oxidization using peracetic acid to the isatoic anhydride. Reaction of sarcosine in DMF and acetic acid leads to the benzodiazepine-2,5-dione. Deprotonation, phosphorylation, and subsequent reaction with diethyl malonate leads to the diester. After selective hydrolysis and decarboxylation the resulting monoester is nitrosated and catalyticaHy hydrogenated to the aminoester. Introduction of the final carbon atom is accompHshed by reaction of triethyl orthoformate to...

Krapcho and Vivelo have described a new formal total synthesis of tropinone (124) and ( )-cocaine (98) (94). Cycloaddition of IV-methylpyrrole (182) and acetylenedicarboxylic acid leads to 183, which is hydrogenated to 184. The diacid mixture 184 is refluxed in MeOH/HCl to yield the diester mixture 185. Addition of this to an excess of metallic sodium in liquid ammonia at — 78°C leads to the N-methylpyrrolidine derivative 186 (cf. 95), whose diethyl analog 147 has earlier been converted to tropinone (124) and (+)-cocaine (98) (78-80) (Scheme 13). 

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