Propynoic esters reaction with

Because the enophiles are normally the electrophilic reagent, their reactivity increases with addition of EWG substituents. Ene reactions between unsubstituted alkenes have high-energy barriers, but compounds such as acrylate or propynoate esters... 

Silver(l) tetrafluoroborate and indium(m) chloride can also promote the reaction of propynoic esters with phenols to afford coumarins. However, substitution of the alkyne is not tolerated for the silver(l) promoted reaction <2003JA4518, 2004SC1909>. 

In the presence of Ni(dppe)Br2 the oxabicyclic alkenes 693 react with propynoic esters to yield 2H-benzo[ ]coumarins 696 (Scheme 172) <2001AGE1286>. The reaction mechanism involves cyclometallation of the propynoic ester and oxabicyclic alkene 693 to form the nickelacyclopentene intermediate 694. (3-Oxy elimination then forms the intermediate 695, which undergoes protonation and isomerization of the double bond followed by intramolecular lactonization to afford the desired 2/7-benzo[ ]coumarins 696 (Scheme 172) <2001AGE1286>. 

Benzyl bromides 15 derived from either salicylaldehydes or 2-methylphenols by reaction with alkyl propynoates afford 277-1 -benzopyrans on treatment with tetrahydrothiophene and K2CO3. A sulfonium ylide is proposed which initiates a Michael addition - elimination -substitution sequence. When CS2CO3 is used as the base, 477-1-benzopyrans result almost exclusively, presumably through isomerisation of the 277-1-benzopyran. The protocol thus offers access to both chromene isomers through simple variation of the reaction conditions <06OL3853>. The Cu-catalysed intramolecular O-arylation of a-(2-bromobenzyl)-P-keto esters in refluxing THF offers a useful route to 2-substituted 477-l-benzopyran-3-carboxylates <06JOC6427>. 

Cuprates of the type Li CuR + i, where > 1, react with the carbonyl group of propynoate esters rather than give the conjugate addition product 61). Extension of the reaction of propynoate esters to vinylcopper compounds and allylcopper compounds affords a stereospecific synthesis of 1,3- and 1,4- dienes, respectively 64, 205). 

Addition reactions. As an alternative to the Baylis-Hillman approach (Z)-2-hydroxy-aUcyl-2-alkenoic esters are assembled from propynoic esters via a Cu(I)-catalyzed Grignard reaction and trapping with RCHO. ... 

The Pd-catalysed reaction of phenols with propynoic acids offers an atom-economic and green route to coumarins. Although the reaction with propynoic acid itself is not regioselective, 3-phenylpropynoic acid gives a single product from w-substituted phenols <04S1466>. The synthesis of coumarins both from alkynes, CO and iodophenols and by the reaction of phenols with propiolic esters is facilitated by Co/Rh nanoparticles <04SL2541>. 

Potassium fluoride. 13, 2S6-2S7 15. i As base. In the absence of solvent silylacetonitrile with aldehydes to give 1 wave as energy source the reaction is cot 18-crown-6 successfully effects the Mic esters and propynoic esters also. 

Reactions between ClCH2PCl2 ", EtPCl2 or PhPCl2 and propynoic acid afford the 3-phosphinoylpropenoyl chlorides 469, whilst the chlorides Ph(RO)PCl similarly yield the phosphinic esters 470. With acetic anhydride, 469 produce the unsaturated cyclic anhydrides 471, hydrolysable, as is 469, to the acids 472. When heated, 470 also yields 471. 

In the past, carbanions of propynoate esters have been difficult to obtain cleanly owing to nucleophilic attack of the base used (e.g. Bu"Li) on the ester function. It has now been found that such anions are readily available using the ubiquitous base lithium di-isopropylamide. Furthermore, subsequent reactions of such anions with a trialkyborane followed by decomposition of the borane complex with iodine afford high yields (70—80%) of substituted alk-2-ynoates. ... 

Photolysis of n5 2,4-dimethylpentadien-l-yl manganese tricarbonyl [Mn(Tl5-2,4-Mc2C5H5)(CO)3] has been reported 59 to afford the THF adduct [Mn(T 5-2,4-Me2C5H5)(CO)2(THF)], which on reaction with butynedioic acid dimethyl ester and diphenylacetylene afforded respectively T 5-l,2-dimethoxycarbonyl-4,6-dimethylcyclohepta-2,4-dien-l-yl manganese tricarbonyl (39) and Ti5-4,6-dimethyl-l,2-diphenylcyclohepta-2,4-dien-l-yl manganese tricarbonyl (40) in formal [5 + 2] cycloaddition reactions. Propynoic acid methyl ester formed the 2 1 adduct T 5 2-i,3.dimethyl-6-methoxycarbonyl-6-( -2 -methoxycarbonylvinyl)-cyclohepta-2,4-dien-l-yl manganese dicarbonyl (41) which was characterised by X-ray diffraction. 

A synthesis of the 3-methylthiopyran-2-one (337) is based on the formation of a 2 1 adduct (336) between methyl propynoate and DMSO which occurs at high ester concentrations (Scheme 102) (66CB1558). Upon heating, cyclization occurs with the overall loss of methoxymethane. Only a small amount of dimethyl furan-2,4-dioate is formed in this reaction, but a furan is the sole product from dimethyl butynedioate and DMSO. 

Ethyl acrylate will react with vinylic cuprates, but at a much slower rate than a, -unsaturated ketones and ethyl propynoates 205). Complex-ation with trimethyl phosphite is advantageous because the reactivities of the cuprate and resulting carbanion are increased. Glutarate esters are important by-products from the reaction of the intermediate carbanion with another molecule of the acrylate the primary addition product was obtained in yields from 3.4% to 38% and the glutarate ester in 7.1-31% yield. 

Cycloaddition. Aldimines and those prepared in situ combine with ethyl propynoate readily. On applying the reaction to arylamines several quinoline-3-carboxylic esters have been prepared.The formation of l,4-dihydropyridine-3,5-dicarboxylic esters involves electrocyclic opening of the 1 1-cycloadducts and a Diels-Alder reaction. 

Reaction of the parent compound with ethyl propynoate gives a 1 1 mixture of 5- and 6-indolecarboxylate esters (Equation (147)) <90JCS(P1)2156>. 

Abubakar AB, Booth BL, Tipping AE (1990) Novel Diels-Alder cycloaddition involving two a, p-unsaturated esters in the formation of isocoumaiins from the reaction of ethyl propyno-ate with 3,4-bis(trifluoromethyl)fhran. J HuorChem 47 353-359... 

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