Carboxylic esters, unsaturated

The reductive coupling of aldehydes or ketones with 01, -unsaturated carboxylic esters by > 2 mol samarium(II) iodide (J.A. Soderquist, 1991) provides a convenient route to y-lactones (K. Otsubo, 1986). Intramolecular coupling of this type may produce trans-2-hy-droxycycloalkaneacetic esters with high stereoselectivity, if the educt is an ( )-isomer (E.J. Enholm, 1989 A, B). 

The prototype of a Knoevenagel reaction shown in the scheme above is the condensation of an aldehyde or ketone 1 with a malonic ester 2, to yield an a ,/3-unsaturated carboxylic ester 4. 

The cyclopropane cyclizations by elimination of triflinic acid (CF3S02H) are readily effected by basic treatment of triflones (trifluoromethyl alkyl sulfones) with activated /-protons (equations 46 and 47)39. The cyclopropane diesters 45 are formed on treatment of 44 with potassium hydride in DMSO or sodium methoxide in methanol (equation 48). In contrast, the monoester 46 failed to give the desired cyclopropane40. Addition of carbanions derived from /f, y-unsaturated phenyl sulfones to a, /i-unsaturated carboxylic esters and subsequent elimination of benzenesulfinate ion give cyclopropanes possessing the unsaturated side chain and the ester function in trans positions (equation 49)41. 

Preparation of l-ethoxy-2-phenyl-4,5-dimethoxycarbonyl-A2- 5-phospholene 1-oxide — Reaction of a vinylicphos-phonite diester with an unsaturated carboxylate ester... 

In 2006, Zeitler demonstrated the use of alkynyl aldehydes in redox esterification [114]. As in previous examples, the author proposes the formation of an activated carboxylate that acts as an acylating agent Eq. 19. A variety of a,P-unsaturated carboxylic esters 199 are formed in moderate yields with E-selectivity up to >95 5. 

The Michael acceptor can be an a, -unsaturated carboxylic ester. This possibility is illustrated with the conjugate addition of phenylmagnesium bromide to ethyl arecaidinate, which leads to 4-phenylnipecotic acid (equation 33). 

The reaction between a phenol and an unsaturated carboxylic ester has been widely used for the synthesis of chromone-2-carboxylic acids (00JCS1119,1179). There is little restriction on the substituents which may be present in the phenol and the necessary basic conditions have been achieved in various ways. 

Keywords alkyl 2-halocarboxylate, unsaturated carboxylic ester, radical addition, lactone... 

Two examples of Pd(II)-catalyzed carbomethoxylations of vinyl(phenyl)iodonium salts have been reported (equations 251 and 252)125,126. The mild reaction conditions and stereospecificity of carbonylation recommend further applications of vinyliodonium compounds for the synthesis of a,/ -unsaturated carboxylate esters. By way of comparison, similar carbobutoxylations of vinyl halides (Br, I) typically require higher temperatures (60-100 °C) and longer reaction times, and they sometimes proceed with low stereospecificity151. 

Tetrahydro-7H-oxazolo[3,2-a]pyrimidin-7-ones (275) can be prepared from 2-amino-2-oxazolines and a,/8-unsaturated carboxylic esters. The orientation of the substituents in the reaction product corresponds to Michael addition of the oxazoline nitrogen as the first step (74LA593). 

The UV-spectrum (64, Table III) and high negative rotation ([aD] — 310° in methanol) of tabersonine hydrochloride (64, 65) indicated at once that the alkaloid contained the same chromophore as akuam-micine (CCXXV) and echitamidine (CCXLII, Chapter 8), and this chromophore was subsequently shown (Volume VII, p. 127) to be Ph—NH—C=C—CO2R. The NH (2.95 /a) and a,/3-unsaturated carboxylic ester bands (6.02 /a and 6.2 /a) were also seen in the IR-spectrum. The NH group was not acetylated under usual conditions and the ester group was unusually resistant to hydrolysis (64). 

The stereocontrol during asymmetric dihydroxylation reactions of /3,7-unsaturated carboxylic esters with trisub-stituted double bonds for the syntheses of 7-butyrolactones has been investigated in detail by Kapferer and Bruckner (Equation 87) <2006EJ02119>. 

The ate-complexes (34) also react with benzylic halides aroyl chlorides allyl halides and proj r l halides to afford the (x>rr ponding products, respectively (Eq. 75). (E)-a,P-Unsaturated carboxylic esters can also be obtains by the reaction of such borate complexes with ethyl propiolate The same type of reaction between copper(I) methyltrialkylborates and l-(l-pyrrolidinyl)-6-chloro--1-cyclohexene gives the corresponding alkylation products which are readily hydrolyzed to 2-alkylcyclohexanone... 

Addition of aldehydes to activated double bonds Aldehydes (I) react with a,0-unsaturated carboxylic esters (2a), ketones (2b), or nitriles under the catalytic influence of sodium cyanide to give y-kelocarboxylic esters (3a), y-diketones (3b). or y-ketonitriles... 

MO calculations have been carried out on the isomerization of cyclopropane to propene, and the MNDO method has been used to study the reaction pathway and to optimize the structure of reactant, transition structure, and product of the ring opening reaction of bicyclo[1.1.0]butane. Various methods have been employed to estimate the rate constants for ring opening of the 2-cyclopropyl-2-propyl radical. 1-Acceptor-1-sulfenyl-substituted 2-vinylcyclopropanes of the type (430) have been found to afford 6-sulfenyl-a,jS y, -unsaturated carboxylic esters and nitriles (431) upon treatment with acid, by a process which involves C(l)—C(2) bond fission and a novel 1,5-sulfenyl rearrangement (see Scheme 110). It has been shown that the benzophenone-sensitized photolysis of vinyl norcaradiene derivatives, such as 5-(2-methylprop-l-enyl)-3-oxatricyclo[4.4.0.0 ]deca-7,9-dien-4-ones (432), results in the regioselective cleavage of only one of the cyclopropyl c-bonds to afford isochroman-3-one derivatives (433). It has been reported that the major product obtained from the reaction of structurally diverse a-diazo ketones with an electron-rich alkene in the... 

Conjugate hydrocyanation of oc -unsaturated carboxylic esters, acid chlorides, and acyl cyanides, is effected by reaction with diethylaluminium cyanide [e.g. (128) — (129)]. The acid chloride and cyanide are the most reactive. A double conjugate addition of nitromethane with a 2-methylene-4-en-3-one (130) gave a... 

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