Dimethyl ester Subject

Hematoporphyrin dimethyl ester (15, 1.52 g, 2.43 mmol) (diastereomeric mixture) and Af.At-dimethyl-acetamide dimethyl acetal (8 mL) were suspended in o-xylcnc (100 mL), degassed and then heated with exclusion of light in a flask equipped with a reflux condenser and a Soxhlet apparatus containing 3 A molecular sieves. The temperature was raised during 15 min from rt to 115 C and kept at this temperature for 30 min. Then the temperature was raised to 155 C and the mixture kept at this temperature for 3 h. The mixture was evaporated in a bulb tube and the residue subjected to column chromatography [silica gel (ICN), CH2Cl2/MeOAc/MeOH 10 5 0.5] with exclusion of light yield of pure 16A 305 mg (17 %) yield of pure 16B, 375 mg (20%) and 187 mg (10%) of a mixture of 16 A and B. 

Hydrocarbon CXXXIV was prepared from abieta-6,8-diene (CXXXV) by the following route. Reaction with maleic anhydride gave the adduct CXXXVI, whose dimethyl ester was ozonized to give CXXXVII in 35% yield. Oxidation of the latter with H2O2-BF3 gave the keto diester CXXXVIII in 60% yield. The diacid of CXXXVIII was subjected to oxidative bis decarboxylation with lead tetraacetate in pyridine to afford the keto olefin CXXXIX. Hydrogenation of CXXXIX over palladium/... 

Storbeck and Ballauff were the first to report on polyesters based on FDCA and dianhydro-hexitols [16]. Here, the acid chloride of FDCA was reacted with all three dianhydrohexitol isomers, in 1,1,2,2-tetrachloroethane in the presence of pyridine, giving white, fibrous polyesters. This work has been discussed in detail in the preceding section on isohexide polyesters (section 9.2.2). Later, Gandini and co-workers performed some kinetic studies on the transesterification of the FDCA dimethyl ester [66-68]. However, little attention was paid to polymer properties. More recently a series of papers on FDCA polyesters has been published by various groups, indicating the renewed interest in this subject. 

The present evidence indicates that molecular weight iS an important factor in controlling the interferon-inducing property or the toxicity factor of the DVE-MA copolymer. The development of a method which would permit fractionation of the copolymer into fractions of narrow molecular weight distribution for further evaluation as an interferon inducer was the purpose of the investigation undertaken by Butler and Wu [49]. Two copolymer samples having i/j i, = 1.56 dl/g and 0.15 dl/g were subjected to fractionation as the polyelectrolyte on one 3 ft column each, in series, of Type AX, BX, CX, DX and EX Deactivated Porasil, without much success. However, by conversion of the copolymers to their dimethyl ester, it was possible to fractionate these derivatives on standard Styragel columns, and to compare the... 

This is the preferred method for the synthesis of both, aliphatic and aromatic polyesters derived from CHDM. The reaction is usually accomplished in two steps. The first step is carried out under a pressure which depends on the diacid or the dimethyl ester derivative used for the synthesis. Usually an excess of diols to diacid (1.2-2.2 1) is employed so a mixture of short oligomers is produced. In the second polycondensation step, which is carried out at higher temperatures and under vacuum, the oligomers react to generate the polymer and the excess of diol is removed. If the resulting polyester is crystalline it may be subjected to solid state postpolycondensation (SSP) in order to increase the molecular weight. 

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

Variety of a-keto esters, such as methyl and ethyl pyruvate, methyl mandalate, dihydro-4,4 - dimethyl-2,3 fiiranedione were used to calculate the shielded form of [CDdosed - a-keto ester] complexes leading to the formation of ( R) or (S) product, respectively. The details of these results will be a subject of a subsequent paper [17]. As emerges from these calculations the favourable directionality is maintained in complexes (R), even for dihydro-4,4 - dimethyl-2,3 fiiranedione. 

These reactions accomplish the same overall synthetic transformation as the acylation of ester enolates, but use desulfurization rather than decarboxylation to remove the anion-stabilizing group. Dimethyl sulfone can be subjected to similar reaction sequences.232... 

L-dihydroxy-succinic acid (L(dexiro)-tartaric acid, CXIII). This result establishes the position of the double bond between C4 and C5 and demonstrates that C4 carries only one hydrogen atom while C5 has attached to it the enolic hydroxyl group. Treatment of the enol CXI with ethereal diazomethane gives 5-methyl-A4-D-glucosaccharo-3,6-lactone methyl ester (CXIY) which upon further methylation with silver oxide and methyl iodide yields 2,5-dimethyl-A4-D-glucosaccharo-3,6-lactone methyl ester (CXV). When the latter is subjected to ozonolysis there is formed oxalic acid and 3-methyl-L-threuronic acid (CXVI). Oxidation of this aldehydic acid (CXYI) with bromine gives rise to a monomethyl derivative (CXVII) of L-ilireo-dihydroxy-succinic acid. 

In 2001, Sarko and coworkers disclosed the synthesis of an 800-membered solution-phase library of substituted prolines based on multicomponent chemistry (Scheme 6.187) [349]. The process involved microwave irradiation of an a-amino ester with 1.1 equivalents of an aldehyde in 1,2-dichloroethane or N,N-dimethyl-formamide at 180 °C for 2 min. After cooling, 0.8 equivalents of a maleimide dipo-larophile was added to the solution of the imine, and the mixture was subjected to microwave irradiation at 180 °C for a further 5 min. This produced the desired products in good yields and purities, as determined by HPLC, after scavenging excess aldehyde with polymer-supported sulfonylhydrazide resin. Analysis of each compound by LC-MS verified its purity and identity, thus indicating that a high quality library had been produced. 

The groups of Giacomelli and Taddei have developed a rapid solution-phase protocol for the synthesis of 1,4,5-trisubstituted pyrazole libraries (Scheme 6.194) [356]. The transformations involved the cyclization of a monosubstituted hydrazine with an enamino-/8-ketoester derived from a /8-ketoester and N,N-dimethylformamide dimethyl acetal (DMFDMA). The sites for molecular diversity in this approach are the substituents on the hydrazine (R3) and on the starting j3-keto ester (R1, R2). Subjecting a solution of the /8-keto ester in DMFDMA as solvent to 5 min of microwave irradiation (domestic oven) led to full and clean conversion to the corresponding enamine. After evaporation of the excess DMFDMA, ethanol was added to the crude reaction mixture followed by 1 equivalent of the hydrazine hydrochloride and 1.5 equivalents of triethylamine base. Further microwave irradiation for 8 min provided - after purification by filtration through a short silica gel column - the desired pyrazoles in >90% purity. 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

Another example of a case where acid-base chemistry competes with cyclization is found in efforts to construct an analog of the Corey lactone [45], The enantiomerically pure unsaturated ester 91 was assembled and subjected to the conditions indicated in Eq. (26). In this instance, dimethyl methylmalonate was used as the proton donor to avoid 1,4-addition of the conjugate base to 91. Cyclization afforded a combined 77% isolated yield of the y-hydroxy ester 92 and the lactone 93 the former could be converted to the lactone in the... 

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