Ester base-promoted

Photoresist appHcations in the microelectronics industry have also been disclosed (340). Thermally stable ben2yl sulfonate esters based on 2-methyl-3-nitroben2otrifluoride [6656-49-1] can serve as nonionic photoacid generators to promote a cascade of reactions during irradiation of the resist. 

Base promoted 1,4-additions ol nucleophiles (usually C) to a.6-unsalurated esters, ketones, nitnies, suHones, nitro-compounds often stereoselective addition. 

Base-promoted fragmentation of products resulting from SRN I reactions between gem-halonitroalkanes and cyclic [1-keto-esters as nucleophiles give rise to di- or trifunctionalized olefins (Eq. 7.141).187 If the product is treated with NaCl in DMSO at 120 °C, the ester and nitro groups are eliminated. 

Carborundum, silver on, 27 10-12 3-Carboxy - 2,2,5,5,- tetramethylpyrrolidin-1-oxy m-nitrophenyl ester, enantiomeric specificity in reactions of cyclohexaamy-lose and cycloheptaamylose on, 23 233 Carboxylate ions, 32 117-118 Carboxybc acids a, 3-unsaturated, 25 109 hydrogenation of, 25 107-115 ketonization of, 24 35-37 Lewis base-promoted ruthenium catalysis, 32 389, 400... 

Darzens reaction of (-)-8-phenylmethyl a-chloroacetate (and a-bromoacetate) with various ketones (Scheme 2) yields ctT-glycidic esters (28) with high geometric and diastereofacial selectivity which can be explained in terms of both open-chain or non-chelated antiperiplanar transition state models for the initial aldol-type reaction the ketone approaches the Si-f ce of the Z-enolate such that the phenyl ring of the chiral auxiliary and the enolate portion are face-to-face. Aza-Darzens condensation reaction of iV-benzylideneaniline has also been studied. Kinetically controlled base-promoted lithiation of 3,3-diphenylpropiomesitylene results in Z enolate ratios in the range 94 6 (lithium diisopropylamide) to 50 50 (BuLi), depending on the choice of solvent and temperature. ... 

The standard means for preparing oxicams 285, initially developed by Lombardino, is through the base-promoted rearrangement reaction of isothiazole dioxides 286, which in turn are prepared from saccharin derivatives such as 287 (Scheme 40) <1981AHC(28)73>. The oxicam core can be further derivatized by N-alkylation of oxicam 285 and amidation of the C-3 ester functionality of 288 to form the common drug scaffold 289. 

As described previously, carboxylic acids may be used as solvents for halide or Lewis base-promoted CO reduction. However, these solvents have the disadvantage of forming the usually less desirable carboxylate esters rather than free alcohol products. Rate or selectivity advantages are not apparent in these solvents. 

Methyl- 1,3-cyclopentanedione is a key intermediate for the total synthesis of steroids.2 A number of methods have been described for its preparation, among them the condensation of succinic acid with propionyl chloride,3 and that of succinic anhydride with 2-buten-2-ol acetate,4 both in the presence of aluminum chloride. It has also been obtained from 3-methylcyclopentane-1,2,4-trione by catalytic hydrogenation5 and Wolff-Kishner reduction 6 The base-promoted cyclization of 4-oxohexanoic acid ethyl ester and diethyl propionylsuccinate with tertiary alkoxides was first reported by Bucourt.7 The present cyclization process provides an experimentally simple route to 2-methyl-1,3-cyclopentanedione. Using the same procedure, 4-oxoheptanoic acid ethyl ester has been cyclized to give 2-ethyl-l,3-cyclopentanedione in 46% yield... 

In an effort to obtain a salvinorin derivative possessing an oe-diol system which can be transformed into the dibenzoate ester required for the exciton chirality CD method, salvinorin A (1) or B (2) was treated with sodium borohydride in various protic solvents. The products having the la,2a-diol group were obtained in high yield. However, this reduction was accompanied by extensive isomerization at C-8. While mechanistic details for this unexpected observation remain to be established at this time, the isomerization at C-8 appears to be the result of the base-promoted clevage of the C-8/9 bond under the reaction conditions followed by the reclosure to provide the 8-epimer prior to the reduction of the 1-ketone. Furthermore, attempts to obtain the 1,2-dibenzoate derivative of the major reduction product 3 under various benzoylating conditions invariably produced only the 2-monobenzoate. 

Scheme 82 Asymmetric synthesis of P-lactams by base-promoted cyclization of P-amino esters...

S,S)-(+)-pseudoephedrine propionamide as chiral auxiliary. The obtained p-amino esters were subjected to a reported base-promoted cyclization [182, 183] affording the p-lactams in good yields and as unique detectable stereoisomer (Scheme 82). 

The guanidine 1 can be alkylated more readily than 2, but nevertheless is a very effective proton acceptor. It is preferred to DBU as the base for esterification of carboxylic acids by an alkyl halide. Thus severely hindered tertiary carboxylic acids can be alkylated by isopropyl iodide in about 90% yield in the presence of 1 (1.5 equiv.). Selective C-monoalkylation of a typical /J-keto ester was effected in 80% yield in the presence of I (1.0 equiv.). Preliminary experiments suggest that 1 is not particularly useful for base-promoted elimination reactions, but that the more hindered 2 is superior to collidine or DBN for this purpose. 

An equimolar mixture of 3,4,5-trimethoxy phenyl iodide 157, lithium propargyl alkoxide 158, and diethyl ethoxymethylene malonate 159 was stirred at room temperature in the presence of a palladium catalyst. Then, to the resulting intermediate 161 potassium t-butoxide was added, and the ensuing base-promoted decarboxylative aromatization afforded tetrahydrofuran MCR adduct 162 in good yield. The ester was first reduced and the furan ring was hydrogenated with Raney nickel to furnish a diastereomeric mixture of products 163 in high yield. Further synthetic manipulations then provided a known precursor to the natural product. 

Carboxylic acid esters have been studied widely and detailed mechanisms have been worked out for these reactions. Equation (4) shows the overall reaction of a carboxylic add ester with hydroxide via the nucleophilic attack of hydroxide at the carbonyl oxygen, with the subsequent loss of the alcohol moiety (HOR). Esters generally have larger ly, than kH+ values, with the result that they hydrolyze by base-promoted reactions at pH 5-6 (Mabey and Mill, 1978). 

Babler, J. H. Base-promoted cyclization of a d-chloro ester application to the total synthesis of ( )-grandisol. Tetrahedron Lett. 1975, 2045-2048. 

Reaction of N-substituted bromomethanesulfonamides with 2 equiv of potassium carbonate and an cr-haloketone, ester, or nitrile leads directly to the /3-sultams 187 substituted at the C-3 position by an EWG. This base-promoted condensation can be used with a-halo ketones, esters, and nitriles where a second Sn2 intramolecular displacement can operate in tandem fashion (Scheme 60). This domino alkylation sequence exhibits a reactivity order where ketone > nitrile > ester (Table 14). The process is particularly efficient when diethyl bromomalonate or 3-chloro-2-butanone are involved <2004CJC113>. 

Hydroxy cyclobutylidenes 635 undergo base promoted rearrangements to afford 2//-pyran-2-ones via formation and ring closure of the intermediate 1,5-keto ester 636 (Scheme 145) <2005TL8237>. 

The reaction typically gives 60% to 70% of the maximum yield. The reaction is a reversible process. An ester reacting with water, giving the carboxylic acid and alcohol, is called hydrolysis it is acid catalyzed. The base-promoted decomposition of esters yields an alcohol and a salt of the carboxylic acid this process is called saponification. 

As an example (Scheme 12), exposure of racemic 72 to sodium methoxide resulted in a smooth fragmentation of the norbomyl backbone to achieve olefinic methyl ester 73, whose elaboration then afforded densely functionalized cyclopentane framework 74. Sodium acetate-mediated displacement of the iodo functionality within 74, followed by elimination of the mesylate group and base-promoted deacetylation finally provided the unsaturated carbasugar 75, which nicely served as a building block for the preparation of a set of neplanocin analogues. 

Deprotonation of the /3-keto ester provides a driving force for the Claisen condensation. The deprotonation is strongly exothermic, making the overall reaction exothermic and driving the reaction to completion. Because the base is consumed in the deprotonation step, a full equivalent of base must be used, and the Claisen condensation is said to be base-promoted rather than base-catalyzed. After the reaction is complete, addition of dilute acid converts the enolate back to the /3-keto ester. 

Saponification is the base-promoted hydrolysis of the ester linkages in fats and oils (review Section 21-7B). One of the products is soap, and the word saponification is derived from the Latin word saponis, meaning soap. Saponification was discovered before 500 b.c., when people found that a curdy material resulted when animal fat was heated with wood ashes. Alkaline substances in the ashes promote hydrolysis of the ester linkages of the fat. Soap is currently made by boiling animal fat or vegetable oil with a solution of sodium hydroxide. The following reaction shows formation of soap from tristearin, a component of beef fat. 

Base-promoted hydrolysis of an ester. Originally used to describe the hydrolysis of fats to make soap. (p. 1206)... 

Addition of an Enolate to Ketones and Aldehydes (a Condensation) 1046 Substitution of an Enolate on an Ester (a Condensation) 1046 Base-Catalyzed Keto-EnolTautomerism 1047 Acid-Catalyzed Keto-EnolTautomerism 1047 Base-Promoted Halogenation 1054 Final Steps of the Haloform Reaction 1056 Acid-Catalyzed Alpha Halogenation 1058 Acid-Catalyzed Aldol Condensation 1063 1,2-Addition and 1,4-Addition (Conjugate Addition) 1085... 

Dienolates. Garcia Ruano and co-workers reported that N-2-methoxynaphthyl sulfinimine (Ss)-163 reacts with the lithium dienolate of 3-butenoic methyl ester (164) to afford a-ethylidene-P-sulfinylamino ester 165 as a single isomer in 82% yield.90 In the presence of ZnBr2, a-vinyl-P-sulfinylamino esters 166 were obtained in 90% as a diastereomeric mixture in a ratio of 30 70. Both (Ss,2S,3R)-166/(Ss,2/ ,3/ )-166 can be converted to the same a-ethylidene-P-amino ester 168 via deprotection of the N-sulfinyl group and subsequent base promoted epimeriza-tion of the a-chiral center.90... 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

Q I Mechanism 22.9 Base-Promoted Hydrolysis of an Ester to a Carboxylic Acid... 

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