A, 3-unsaturated carboxylic acids and

The chiral titanium reagent (6) also catalyzes the [2 + 2] cycloaddition reaction of 1,3-oxazolidin-2-one derivatives of a,(3-unsaturated carboxylic acids and ketene dithioacetals in the presence of MS 4A to give cyclobutanone dithioacetal derivatives with high optical purity (eq 10). Vinyl sulfides, alkynyl sulfides, and 1,2-propadienyl sulfides can also be employed in this reaction to give the corresponding cyclobutanes, cyclobutenes and methylenecyclobutane derivatives with high optical purity (eqs 11 and 12). ... 

Conjugation of the alkene double bond with an electron-withdrawing group reduces the rate of epoxidation. Thus, a, 3-unsaturated carboxylic acids and esters require a stronger oxidant, such as trifluoroperoxyacetic acid, for oxidation. 

Conjugate addition of the R group from RMgX to a,(3-unsaturated carboxylic acids and amides is observed when mixed with three equivalents of MeLi in THF. The methyl group of MeLi does not compete/ ... 

Because of the mild reaction conditions, and its broad applicability, the Knoevenagel reaction is an important method for the synthesis of a ,/3-unsaturated carboxylic acids. Comparable methods are the Reformatsky reaction, the Perkin reaction, as well as the Claisen ester condensation. The Knoevenagel reaction is of greater versatility however the Reformatsky reaction permits the preparation of a ,/3-unsaturated carboxylic acids that are branched in a-position. 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

The Lewis acid-mediated condensation reaction of a,/3-unsaturated carboxylic acids with 4-hydroxy-2-pyrones has been utilized to prepare Fleischmann s a,a-bispyrone 2 and Praill s a,7-bispyrone 3 and confirm their assignments <2000TL1901>. 

Formation of carboxylic acids and their derivatives. Aryl and alkenyl halides undergo Pd-catalyzed carbonylation under mild conditions, offering useful synthetic methods for carbonyl compounds. The facile CO insertion into aryl- or alkenylpalladium complexes, followed by the nucleophilic attack of alcohol or water affords esters or carboxylic acids. Aromatic and a,/3-unsaturated carboxylic acids or esters are prepared by the carbonylation of aryl and alkenyl halides in water or alcohols[301-305]. 

Evidence for this mechanism is (1) two equivalents of RLi are required (2) the hydrogen in the product comes from the water and not from the adjacent carbon, as shown by deuterium labeling 209 and (3) the intermediates 31-33 have been trapped.210 This reaction, when performed in tetramethylenediamine, can be a synthetically useful method211 of generating vinylic lithium compounds (33), which can be trapped by various electrophiles such as D20 (to give deuterated alkenes), C02 (to give a, 3-unsaturated carboxylic acids—6-34), or DMF (to give a, 3-unsaturated aldehydes—0-105). 

In 1996, Borrell and co-workers published58 a two-step procedure to form pyrido[2,3-d]pyrimidines. Mont and co-workers have recently transformed this reaction to a single-step three-component reaction59. a, 3-Unsaturated carboxylic acid esters were... 

Certain functional groups can be accommodated during HI addition. While alcohols are converted to alkyl iodides under the usual reaction conditions,181 sulfones present no problems.133 134 Remote carboxylic acid functionality has no effect on the addition of HI,182 and a,3-unsaturated carboxylic acids produce good yields of exclusively the 3-iodocarboxylic acids, no matter what the substitution pattern about the C—C double bond (equation 136).114,140,183-186... 

Prochiral organic acids were hydrogenated on clay-supported Rh-chiral phosphine complexes.205,206 Hectorite-supported chiral Rh(I)-phosphine complexes were used for the asymmetric hydrogenation of a, 3-unsaturated carboxylic acids.207 It was found that the interaction between the a-ester group of itaconates and phenyl groups of phosphine can play an important role in the determination of the configuration of products. 

I 2]-Photocycloadditon of a, 3-Unsaturated Carboxylic Acid Derivatives (Substrate Classes A4, A5, and A6)... 

Another site-selective reaction of 35 with a,/3-unsaturated carboxylic acid derivatives in the presence of a Lewis acid has been reported (Scheme 25) [35]. The intermediate 37 possesses two nucleophilic sites the zirconium alkyl and the enol ether moieties. Starting from 37, two competing pathways lead accordingly to cyclopropane (38, path a) and/or cyclobutane (39, path b) derivatives. The... 

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