Reaction with esters, -substituted

Diamides and triamides have been obtained from the action of an aqueous saturated solution of ammonia on the corresponding ester (Scheme 18) (88). Amides can also be obtained by the Curtius (16) or Hofmann reactions (80). Thus the Curtius reaction with 2-substituted 4-thiazolecarboxylic acids gives the 4-acetamido compounds (16). 

The Claisen rearrangement of allyl vinyl ethers is a classic method for the stereoselective synthesis of y,J-unsaturated esters. The allylic C-H activation is an alternative way of generating the same products [135]. Reactions with silyl-substituted cyclohexenes 197 demonstrate how the diastereoselectivity in the formation of 198 improves (40% to 88% de) for the C-H insertion reactions as the size of the silyl group increases (TMS to TBDPS) (Tab. 14.14). Indeed, in cases where there is good size differentiation between the two substituents at a methylene site, high diastereo- and enantioselectivity is possible in the C-H activation. 

Tamura et al. (170-172) discovered that, when reactions of ester-substituted nitrones with allylic alcohols are performed in the presence of an equimolar amount of titanium tetraisopropoxide under heating or at room temperature, transesterification takes place to form new nitrones bearing an inner alkene dipolarophile. The resulting nitrone substrates undergo regio- and stereoselective intramolecular cycloaddition reactions to give the ring-fused isoxazolidines (Scheme 11.52). This tandem transesterification/[3 + 2]-cycloaddition method leads to the selective... 

Semicarbazide, like other hydrazines, reduces Fehling solution and, unless substituted in the 1-position, undergoes the typical hydrazine reactions with esters, carbonyl compounds and halides, etc. On heating, it decomposes to hydrazine and biurea. 

Another useful reaction for the difunctionalization of olefins involves a group transfer carbonylation starting from a a-(phenylseleno)carbonyl (or related derivatives) and a terminal alkene under 80 atm of CO. An alkyl radical is first formed by the photocleavage of a C-SePh bond. The addition of this radical to the olefin, followed by the incorporation of CO and radical coupling with PhSe-, gave substituted selenoesters via a three-component coupling reaction [74], The intermolecular formation of C—C bonds via phenylseleno group transfer has been likewise adopted in the reaction between ester-substituted O,Se-acetals and an olefin [75],... 

Two main problems restricted the synthetic usefulness of the sulfinyl male-ates, the low regioselectivity of the elimination of the sulfinyl group in reactions with 1-substituted dienes, and its moderate reactivity (almost identical to that of the sulfinyl acrylates, despite the additional ester group). The use of TiCl4 overcame the second problem, but this catalyst is not compatible with alkoxy substi-... 

In a mechanistic study on the Lewis acid catalyzed addition of ethyl diazoacetate to ketones a similar profile of rearrangement to the 3-keto esters was observed (Scheme 9). In the same reaction with acetophenones, substitution on the benzene ring was found to only slightly affect the otherwise 90 10 preference for migration of aryl versus methyl. ... 

The shortcomings of the method in Chart IV have been overcome by an acid-catalyzed ester-amide cyclization step as outlined in Chart V. For example, reaction of ethyl hydrazinoacetate hydrochloride with potassium cyanate proceeded smoothly in aqueous solution to give ethyl 3-aminohydantoate which was converted into the respective 3-(benzylideneamino)hydantoate, by reaction with a substituted ben-... 

The linker was prepared starting from serine benzyl ester 68 according to Scheme 30. First, the hydroxyl function was protected as a silyl ether. The amino group was then reacted with phosgene to allow for further reaction with a substituted phenol (the educt). Finally, the benzyl ester was subjected to hydrogenolysis yielding unit 69, with the latter bearing a carboxylic acid function for attachment to the solid support to yield 66 ready for use in combinatorial synthesis. 

In addition to aldehydes and ketones, organic compounds which are known to react with Reformatsky reagents include esters,nitriles, acid chlorides, organic halides,epoxides, nitrones, azirenes" and imines. This section describes the selectivity reported for Reformatsky reactions with functionally substituted aldehydes or ketones. 

The replacement of the 4-chloro substituent by reaction with TV-substituted /1-alanine esters and the subsequent Dieckmann cyclization yields alkyl 5-oxo-5,8-dihydropyrido[2,3-J]pyrimidine-6-carboxylates.15 3 -157... 

Dipolar Cycloaddition. The principal use of p-bromobenzenesulfonyl azide is in 1,3-dipolar cycloaddition reactions with functionally substituted alkenes. The reagent has been used at ambient temperature and pressure to convert simple trimethylsilyl and methyl enol ethers of cyclic ketones to ring-contracted p-bromobenzenesulfonimidates, and thence to the corresponding amides, esters, or acids (eqs 1 and 2). 

Another route to this cyclohexyl derivative involves the preparation of 6.183 via an olefmation reaction with a substituted phenylalinal derivative followed by reduction of the phenyl ring. The alcohol moiety in 6.183 was converted to the N-phthal-oyl derivative (6.184) by a Mitsunobu inversion.m Conjugate addition with a higher order silyl cuprate gave 6.185. The silyl moiety was converted to an alcohol (6.186) by treatment with tetrafluoroboric acid and then KF/m-chloroperoxy-benzoic acid. Removal of the phthalimidoyl group with hydrazine led to an amino-ester, which cyclized to lactam 5.757.11 Hydrolysis gave 4-amino-5-cyclohexyl-3-hydroxypentanoic acid (6.188) in 60% yield. 

Transition metal-catalyzed allylic substitution reactions with carbon nucleophiles are among the most important carbon-carbon bond formation methods in modem organic synthesis, because of their broad substrate scope under mild reaction conditions. In addition, they are applicable to enantioselective reactions, as well as exhibiting versatility towards the alkene functionality adjacent to the chiral centre for stereoselective derivatization. Tsuji-Trost allylic substitution, involving a (Ti-allyl) metal intermediate, has provided a particular advance in this regard [34, 35]. Most recently, Sawamura et al. [36, 37] have improved the regioselectivity of this reaction with unsymmetrically substituted allylic esters, and thus opened a new approach to sertraline. 

Model reactions with p-substituted methyl cinnamates 322 furnished the corresponding 3-aryl[2,3- H]propionic acid methyl esters 323 in chemical yields of 50-65% but in specific activities only 17-25% of theoretical. This outcome may be the result of the... 

The reaction of ammonia and amines with esters follows the same general mech anistic course as other nucleophilic acyl substitution reactions (Figure 20 6) A tetrahe dral intermediate is formed m the first stage of the process and dissociates m the second stage... 

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