3- alkynoates

Butyrolactones are prepared by intramolecular reaction of haloallylic 2-alkynoates. The a-chloromethylenebutyrolactone 301 is prepared by the intramolecular reaction of300[150,151]. 4 -Hydroxy-2 -alkenyl 2-alkynoates can be used instead of haloallylic 2-alkynoates, and in this reaction, Pd(II) is regenerated by elimination of the hydroxy group[152]. As a related reaction, the q-(chloromethylene)-7-butyrolactone 304 is obtained from the cinnamyl 2-alkynoate 302 in the presence of LiCl and CuCbflSS]. Isohinokinin (305) has been synthesized by this reaction[l 54]. The reaction is explained by chloro-palladation of the triple bond, followed by intramolecular alkene insertion to generate the alkylpalladium chloride 303. Then PdCb is regenerated by attack of CuCb on the alkylpalladium bond as a key step in the catalytic reaction. 

METHYL 2-ALKYNOATES FROM 3-ALKYL-2-PYRAZ0LIN-5-0NES METHYL 2-HEXYNOATE... 

While the Michael-addition of a,P-unsaturated carbonyl and related compounds constitutes one of the most important fundamental synthetic reactions in organic chemistry, the y-addition developed by Trost and Li of nucleophiles to 2-alkynoates catalyzed by a phosphine provides... 

Iodo-2-alkynoates (e.g., compound 380) react with 6-chloropropylamines (e.g., compound 381) to give quinolizine derivatives in a single synthetic operation (Scheme 88). The process comprises a sequence of an Sn2 reaction that yields secondary amine 382, an intramolecular Michael addition to give the piperidine derivative 383, halogen... 

The annulation reaction of thioamides with 2-alkynoates and 2,3-dienoates under the catalysis of phosphine provides 4,5-dihydro-1,3-thiazoles, particularly those with 2-aryl substituents (Scheme 14).35... 

The allylic 2-alkynoates 77 are a group of special enynes with an ester linkage between their double bond and triple bond. When halopalladation of the triple bond is followed by C-C double bond insertion and the cleavage of the carbon-palladium bond, a series of y-lactones (78-81) can be obtained. 

The Stille adduct of 2-bromothiophene and l-ethoxy-2-tributyl-n-stannylethene or 1-ethoxy-l-tri-n-butylstannylethene is a masked thienyl aldehyde or a masked ketone, respectively [77-80]. Vinylstannane 93, derived exclusively as the -isomer from hydrostannation of bis(trimethyl-silyl)propargyl amine (92), was coupled with 2-bromothiophene to form ( )-cinnamyl amine 94 upon acidic hydrolysis [81, 82], In another case, stereoisomerically pure phenyl ( )-2-tributylstannyl-2-alkenoate 95, arising from Pd-mediated hydrostannation of phenyl ( )-2-alkynoate, was joined with 2-iodothiophene to deliver the stereodefmed trisubstituted a,p-unsaturated ester 96 [83, 84],... 

Palladium (II)-catalyzed ring closure of acyclic allylic 2-alkynoates of type 137 provides an efficient entry to stereodefined a-methylene-y-butyro-... 

Yamanaka and co-workers (74) effected the 1,3-dipolar cycloaddition between miinchnones 134 and polyfluoro-2-alkynoic acid esters to afford the corresponding 4-(polyfluoroalkyl)pyrrole-3-carboxylates (135). The reaction proceeds rapidly at low temperature and the various miinchnones (134) were generated from 1,3-oxazolium perchlorates 133 using the method of Boyd and Wright (6,7). Under... 

Reaction of 2-alkynoic acids with an excess of sodamide in hquid ammonia followed by treatment with mineral acid (after evaporation of the ammonia) gives 3-alkynoiC acids in excellent yields [183], Presumably, the 2-alkynoic acid is convened into the disodium compound of the 3-alkynoic acid via a process of proton removal and proton donation ... 

The same 3-alkynoic acids can also be obtained (in lower yields) by heating 2-alkynoic acids with an excess of aqueous potassium hydroxide [184]. 

Addition of a 2-alkynoic acid to alkali amide in liquid ammonia initially gives a solution of the alkali salt of the carboxylic acid. If an excess of alkali amide is present, the weakly basic salt is further deprotonated at a position next to the triple bond 183], This double deprotonation which may be compared with the formation of di-anions from 1,3-diketones and alkali amides [71], is essentially complete. The high kinetic stability of the alkynoic acid-dianion may be explained on the basis of resonance stabilization ... 

Results of fluorination of P-keto esters with sullur tetrafluoride depend on the presence of hydrogen on the a-carbon Unsubstituted aceto- and propiony-lacetates give 3,3-difluoroalkanoates, 3 fluoro 2-aIkenoates, and 2 alkynoates... 

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