Orthoamides of six alkynecarboxylic acids, possessing reactive substituents in 3-position, are transformed by elemental iodine to the corresponding vinylogous guanidinium iodides. The constitution of two of the iodides was established by crystalstructure analysis.

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Orthoamides. LI. Push‐Pull‐Butadienes and Heterocycles from Alkyne Carboxylic Acid Orthoamides and CH2‐acidic Compounds The acetylides 4b, 4f react with N,N,N′,N′,N″,N″‐hexamethylguanidiniumchloride (5) to give the orthoamides 6b, 6f, resp. From CH2‐acidic compounds and the orthoamides 6a, c, e can be obtained the push‐pull‐substituted butadienes 8a–8aj. The 2,3,5‐trimethyl‐thiadiazolium salt 9 does not condense with 6e, as other CH2‐acidic compounds do, instead the vinylogous guanidinium salt 10a is produced. On heating, the ketenaminals 8d, aa cyclize to give the pyridone‐carbonitriles 11a, b, resp. From 4‐amino‐coumarins 12 and the orthocarboxylic acid amideacetals 13a, b and the ketenaminal 16 resp., the amidines 14a–c and the heterocyclic compounds 15a–c resp., are formed. The enamines 17a–c, 19a, b react with the orthoamides 6a–f to give the pyridine derivatives 18a–1, 20a–h and 21a, b, resp. Analogously, from 6‐aminouracil 22 and 6a, b, e, f are formed the pure 7‐dimethylaminopyrido[2,3‐d] pyrimidines 23a, b or mixtures of compounds 23c, d and the isomeric 4‐dimethylamino‐pyrido[2,3‐d]pyrimidines 24a, b resp., which can be separated via their salts 25a,b/26a,b. The heterocyclic compounds 30a–d, 32a,b can be prepared from the pyrazole derivatives 28, 31 resp. and the orthoamides 6a–f.

Orthoamides 7b-e of alkyne carboxylic acids are transformed by benzoyl chloride to give the corresponding amidinium chlorides 13b-f, which were isolated as the tetraphenylborates 14. The reaction of the orthoamide derivative of phenylpropiolic acid 7a with acetic acid anhydride results in the formation of the acylated ketene aminal 20. The orthoamide of propiolic acid 22 and chloroform react, affording the vinylogous guanidinium salt 24. By the hydrolysis of the orthoamide derivative of phenylpropiolic acid 7a the β-keto-carboxylic acid amide 31A, which is in equilibrium with its enol form 31B, was obtained. Primary and secondary amines react with the phenylpropiolamidinium chloride 13a under conjugated addition, delivering vinylogous guanidinium salts 33.

The orthoamide derivatives 1s and 2e were prepared from the guanidinium salt 7a and the appropriate carbanions. Cleavage of the orthoamide 2e with benzoyl chloride affords the amidinium salt 10a, which can be transformed into the amidinium salt 10b by an anion exchange reaction. The enamines 11a-i, 12a-c, 13a, b, 14a-c, 15a, b, 16, 17a, b, 18a, b, 19a, b, 20 were prepared by condensation of CH2-acidic compounds with the carboxylic acid orthoamides 2a-j. The orthoamide 2d reacts with 1-nitropropane to give the amidinium salt 27a which is transformed into the salt 27b. From benzyl cyanide and orthoamides 2g, i the enamines 30 and 32 were obtained. Similar condensation reactions were performed with the orthoamides of alkyne carboxylic acids 1b, 1c, 1d, 1e, 1p, 1s, giving the push-pull-butadiene derivatives 35a-f, 36a-f, 37a-j, 38a, b, 39a, b, 40a, b. Crystal structure analyses of the butadiene derivatives 37a, 39a, b, 40a, b and 42 were performed, showing that in 37a, 39b, 40a, b by far the shortest bond distance is between C-2 and C-3 of the butadiene system. In 39a the bonds between C1-C2, C2-C3 and C3-C4 are nearly of equal length, whereas in the 1,3-diene unit of 42 the shortest bonds are between C1-C2 and C3-C4.