Propynoates

Endo-trig cyclization of anion 29, formed from 3-methylpyridazine by LDA in THF with methyl 3-propynoate provided 6H-pyrido[l,2-fc]pyrida-zin-6-one 30 (06TL5063). 

Cyclocondenzation of 2-pyridylacetonitrile and ethoxycarbonyl isothiocyanate in MeCN gave 4-cyano-l-oxo-2,3-dihydro-lH-pyrido[l,2-c]pyrimi-dine-3-thione in 18% yield (08MI2). 6-Endo-trig cyclization of anion, formed from 4-methylpyrimidine by LDA in THF at —78 °C, with methyl 3-propynoate provided 8-methyl-6H-pyrido[2,l-c]pyrimidin-6-one in 47% yield (06TL5063). 

Alkynes with EWGs are poor substrates for the coupling with halides. Therefore, instead of the inactive propynoate, triethyl orthopropynoate (350) is used for the coupling with aryl halides to prepare the arylpropynoate 351. The coupling product 353 of 3,3-dicthoxy-l-propyne (352) with an aryl halide is the precursor of an alkynal[260]. The coupling of ethoxy) tributylstan-nyl)acetylene (354) with aryl halides is a good synthetic method for the aryl-acetate 355[261]. 

At low temperatures, oxidation with chromic acid gives propynal [624-67-9] C2H2O (14), or propynoic acid [471-25-0] C2H2O2 (15), which can also be prepared in high yields by anodic oxidation (16). 

H-pyran synthesis from, 3, 759 Propyne, 3-(2-amino-1 -benzimidazolyl)-isomerization, 5, 450 Propynoic acid, phenyl-ethyl ester... 

The Diels-Alder cycloadclition reaction occurs most rapidly if the alkene component, or dienophile ("diene lover"), has an electron-withdrawing substituent group. Thus, ethylene itself reacts sluggishly, but propenal, ethyl propenoate, maleic anhydride, benzoquinone, propenenitrile, and similar compounds are highly reactive. Note also that alkynes, such as methyl propynoate, can act as Diels-Alder dienophiles. 

Diels-Alder cycloaddition of 3,4-bis(trifluoromethyl)furan with ethyl propynoate involved addition of two a,/3-unsaturated esters followed by acid-catalyzed ring opening, rearrangement, and elimination of ethanol to give a 6,7-bis(trifluoromethyl)isocoumarin-3-carboxylate [92JFC(56)359]. 

Fig. 9. Variation of Xmax in the fluoroscence spectra of solutions of poly(propynoic acid)s in water 1(1) and (2)] and methanol [(3) and (4)1 as a function of the ph of the solution. (1) and (3) Poly(propynoic acid) obtained by polymerization in liquid phase (PPAL) (2) and (4) poly(propynoie acid) obtained by polymerization in solid phase (PPAS)...

We have shown with polyfbarium propynoate)s as an example40,41 that the conjugation efficiency may vary considerably, depending on the presence of inter-or intramolecular salt bonds in the polymers. 

Figures 11 and 12 contain data testifying to the change in conjugation efficiency following the formation of a solid phase by polymers of propynoic acid. It follows...

Fluorescence and phosphorescence spectra of poly(propynoic acid)(FPA), polyphenylene (PP), and DPAcN show that the difference of energies between the lower excited singlet and triplet states, as observed in the case of PP (583 nm) and DPAcN (528 nm), is considerably greater than that of poly(propynoic acid) (270—300 nm) which besides transitions may undergo rr - transitions. PCSs showing only... 

Together with the decarboxylation, dehydration of PPA takes place on heating. Examination of the decarboxylation of copolymers of acrylic and propynoic adds having blocks in their structure has revealed two interesting phenomena261 262. ... 

Decarboxylation of copolymers of propynoic acid and phenylacetylene of varying composition was found to manifest an increase in reactivity of the carboxylic groups with increasing concentration of conjugated double bonds in the chain. 

We have considered the factors determining the participation of PPA in photochemical processes40- 42, 45). Poly(propynoic acid) has served as an example of the perturbation of a conjugated system resulting from photoinitiated oxidation. 

Fig. 16. Change of optical density (JD) of aqueous solutions of poly (potassium propynoate) for different wavelengths in the process of oxidation during irradiation with white light...

We have also used poly(propynoic acid) in our studies of the photochemical interaction of PCSs with dienophiles, such as maleic anhydride, tetracyanoethylene, and styrene. This photochemical reaction of Diels-Alder type is accompanied by the breakdown of the conjugation system and the formation of slightly colored adducts266. Together with the cycloaddition reaction, photodegradation of PPA and its adducts takes place. A cycloaddition reaction is always preceded by the formation of a donor-acceptor complex of a PCS with a dienophile. 

Bearing in mind the semiconductive properties of PCSs one might expect that these substances, being p-type semiconductors in air, possess photosensitizing activity. We, indeed, have demonstrated40 that PCSs, such as poly(schiff base)s, salts of poly(propynoic acid), or polyquinoline, are active photosensitizers of... 

Nitro-Phenylpropioiic Acid (2-Nitrophenyl propynoic acid). 

Propanamine, 3-chloro-lV,A,-dimethyl- ], hydrochloride, 55, 128 2-Propynoic aud, 4-chlorophenyl-, 55, 76 2-Propynoic aud, phenyl-, methyl ester, 55,... 

In the case of the reaction of 2-vinylindole (83, R = Ri = H) with methyl propynoate, a diester is obtained by a multiple one-pot process involving two molecules of the dienophile and the extrusion of ethene (Equation 2.23). 

Diels-Alder reactions of 1,3-cyclohexadienes and 3-(trimethylsilyl)propynoates. A new synthesis of orf/7o-(trimethylsilyl)benzoate esters [149]... 

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