Propiolic acid propargyl esters

From propiolic acid propargyl esters an elegant route to a-pyrones has been developed by Schreiber and coworkers.36 The conversion is shown in Scheme 12.19. 

Rh complexes are examples of the most effective catalysts for the polymerization of monosubstituted acetylenes, whose mechanism is proposed as insertion type. Since Rh catalysts and their active species for polymerization have tolerance toward polar functional groups, they can widely be applied to the polymerization of both non-polar and polar monomers such as phenylacetylenes, propiolic acid esters, A-propargyl amides, and other acetylenic compounds involving amino, hydroxy, azo, radical groups (see Table 3). It should be noted that, in the case of phenylacetylene as monomer, Rh catalysts generally achieve quantitative yield of the polymer and almost perfect stereoregularity of the polymer main chain (m-transoidal). Some of Rh catalysts can achieve living polymerization of certain acetylenic monomers. The only one defect of Rh catalysts is that they are usually inapplicable to the polymerization of disubstituted acetylenes. Only one exception has been reported which is described below. 

PdCl2 Propargyl alcohol, propiolic acid, propiolic acid ester ( 90%) 132,133... 

PPh3)2PdCl2 Propiolic acid ester ( 80%), propargyl alcohol 133... 

Potassium hydroxide, 20, 239, 303-304 Potassium persulfate, 274 Potassium superoxide, 304-307 Potassium tri-sec-butylborohydride, 307 Prins reaction, 159 Progesterone, 107 Proline, 10, 307 1,3-Propanediol, 37 Propargylic alcohols, 8, 53 Propargylic chlorides, 155 (E)-Propenyllithium, 141 Propiolaldehyde diethyl acetal, 79-80 Propiolamidium salts, 124 Fropiolate esters, 8 Propiolic add, 295 Propylene carbonate, 74 Propylene oxide, 74 Protolichesterinic add, 412 Pterocarpins, 114 Pulegone, 287, 288, 308-309 tosylhydrazones, 375-376 Pulvinic acid pigments, 291 Pumiliotoxin, 28... 

The reaction of methyl propargylate (propiolate) with benzylimidazole and its 2-alkyl and aryl derivatives in acetonitrile leads to the formation of the methyl esters of 3-fran -(l-benzimidazolyl)acrylic acid 106a and 107a, b, whereas the reaction with benzimidazole in methanol leads exclusively to the corresponding cis isomer 106b in the absence of the solvent, the treatment of benzimidazole with methyl propiolate gives a mixture of compounds 106a, b, and pyrrolo[l,2-a]ben-zimidazole 108 (Fig. 3.5). At the same time, the 2-isopropyl, 2-phenyl, and 2-benzyl derivatives of benzimidazole in reaction with methyl propiolate without a solvent form the pyrrolo[l,2-a]quinoxalines 114 and 115 (Scheme 3.35) (Acheson and Verlander 1973). 

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