Volume 73, Issue 7 - Special Issue: Iminium Salts and Imines

1-Arylazo-substituted 2-naphthylamines, which are easily obtainable by the coupling of arene diazonium salts with 2-aminonaphthalene-sulfonic acid, can be transformed by reaction with reactive carboxylic acid derivatives or nitrosation reagents into novel 2-aryl-substituted naphtho[2,1- e ][1,2,4]triazinium and naphtho[2,1- e ][1,2,3,4]tetrazinium salts, respectively.

β -Ionone and camphor were ethynylated to give the alkynols 14 , 16 , 17 which can be transformed to the alkynolethers 5b , 5i , 5j , 5k , 5l , 5m by treatment with dimethylsulfate and chlorotrimethylsilane, respectively. From the alkynolethers 5h , 5i , 5j / 5k , 5l / 5m the orthoamide derivatives 4h , 4i , 4j / 4k , 4l / 4m can be prepared by treatment with N,N,N ′ ,N ′ ,N ″ ,N ″-hexamethylguanidinium chloride ( 8 ) in the presence of sodium hydride. The orthoamides 4h , 4i react with the sulfonamide 30 under condensation yielding the N -sulfonylated acrylamidines 31 , 32 . From the orthoamide 4h and p -nitroaniline the propiolamidine 29 could be obtained. The orthoamides 4j / 4k and 4l / 4m , react with benzamidine to give the pyrimidines 33 , 34 , respectively. In the reaction of malonodinitrile ( 9a ) with the orthoamides 4i and 4j / 4k , mixtures of 1,1-diamino-1,3-butadienes 36 , 38 and 1,3-diamino-1,3-butadienes 37 and 39 are produced, respectively. From CH 2 -acidic compounds as ethylcyanacetate ( 9b ), diethyl-malonate ( 9c ) and nitromethane ( 9d ) and the orthoamide 4i the 1,1-diamino-1,3-butadienes 36b – d were produced. The pyridone derivative 40 can be prepared from cyanoacetamide ( 9e ) and the orthoamide 4i . The condensation of the orthoamides 4j / 4k with cyanoacetamide ( 9e ) affords a mixture of the pyrimidone 41 and the nicotinonitrile 42 .

The preparation of the vinylogue guanidinium salt 10c is described. The reaction of the vinylogue orthocarbonic acid amide derivative 12 with CH 2 -acidic compounds 14a–s affords the ketene aminals 15a–s . At room temperature the succinimide 19a is deprotonated by 12 to give the vinylogue salt 10e . The bis-ketene aminal 20 is formed in the reaction of 19a with 12 at elevated temperatures. Succinic acid esters 21 do not react cleanly with the orthoamide 12 , but mixtures of ketene aminals 23 and bis-ketene aminals 22 are formed. From succinodinitrile ( 24 ) and 12 the bis-ketene aminal 25 could be obtained, which is also accessible by the action of the salt 10c with 24 in the presence of sodium hydride.

[3+2] cycloadditions of ynones derived from glycine and ( S )-alanine and some other dipolarophiles with azomethine imines, nitrile oxides, diazoacetate, and azidoacetate were studied. The dipolarophiles were obtained from α -amino acids, either by the reduction of the carboxy function with ethynylmagnesium bromide or by propiolation of the amino function. Cu-catalyzed cycloadditions of ynones to azomethine imines were regioselective and gave the expected cycloadducts as inseparable mixtures of diastereomers. In some instances, further oxidative hydrolytic ring-opening took place to afford 3,3-dimethyl-3-(1 H -pyrazol-1-yl)propanoic acids. Acid-catalyzed cycloadditions of 3-butenone were also regioselective and provided mixtures of diastereomeric cycloadducts, which were separated by chromatography. In the reactions of title ynones with alkyl diazoacetates, in situ -formed benzonitrile oxides, and tert -butyl azidoacetate, all cycloadducts were obtained as single regioisomers. The structures of all novel compounds were established by nuclear magnetic resonance and X-ray diffraction.

The three isomers 1-methylquinolinium-2-, 3-, and 4-ethynyl(phenyl-4-carboxylates) belong to two distinct types of heterocyclic mesomeric betaines. The quinolinium substituted in position 3 is a cross-conjugated mesomeric betaine (CCMB), whereas the quinolinium derivatives substituted in positions 2 and 4 are members of the class of pseudo-cross-conjugated mesomeric betaines (PCCMBs). While the charges are strictly separated within the common π-electron system of the CCMB according to the canonical formulae, the charges are effectively but not exclusively delocalized in the PCCMBs because cumulenoid resonance forms including electron sextet structures without external octet stabilization can be formed in accordance with the definition of PCCMBs. As a consequence, despite being closely related structures, the three isomers differ in their chemical and spectroscopic behaviors. Thus, on trying to hydrolyze the ester group of the methyl quinolinium-2-ethynyl-benzoate into the corresponding acid by subsequent treatment with sodium hydroxide in methanol and aqueous hydrochloric acid at pH 3, the acetal methyl 1,1-dimethoxy-2-(quinolinium-ylidene)ethyl]benzoate and the corresponding β -enamino carbonyl compound were formed, respectively. The corresponding acids of the 2- and 4-substituted quinolinium-ethynyl-benzoates were obtained by a modified procedure. On deprotonation, the resulting cross-conjugated quinolinium-3-ethynyl-benzoate betaine proved to be stable, whereas the corresponding pseudo-cross-conjugated quinolinium-2- and -4-ethynyl-benzoate betaines decomposed. Frontier orbital profiles were calculated, and IR and Raman spectra of the starting materials were measured and calculated to analyze the differences of CCMBs and PCCMBs of mesomeric betaines possessing triple bonds. A higher contribution of the cumulenoid resonance forms to the overall structure of the PCCMBs was determined.

In this study, we report on the syntheses of novel angular fused azaacenes. For this purpose, the synthesis of the bis -diamine 2 (TABEF) could be shortened and optimized. The condensation reaction of 2 with different types of 1,2-diketones yielded new azaacene derivatives of types 10 , 11 and 12 . Analogously, 2 was cyclized with thionyl chloride to give the piazthiol derivative 13 . The optical and electrochemical properties of all new compounds were investigated by UV/Vis absorption, fluorescence emission spectroscopy and cyclovoltammetric measurements.

The thermal metal-free [2+2] cycloadditions of electron-poor acetylenes to some polysubstituted systems with conjugated double bonds (polysubstituted butadienes) are described.

Protic ionic liquids with nitrate anions were used as solvents and catalysts for a three-component oxidative dehydrogenation tandem reaction via the coupling and hydroarylation of benzaldehyde, aniline, and phenylacetylene to a quinoline derivative. The reaction was supported by air and microwave irradiation. The presence of nitrate as counter anion in the protic ionic liquids was essential for the reaction.

Enzymes that use pyridoxal phosphate (PLP, Vitamin B 6 ) as cofactor constitute a ubiquitous class of biocatalysts. A variety of PLP-dependant enzymes mainly involved in biochemical pathways concerning amino acid metabolism are found in all forms of life. These enzymes also play an important role in wine production, as well in grape growing as in enological processes. The formation of pleasant aroma compounds often runs with participation of pyridoxal-dependant enzymes. But these are also brought into context with the formation of off-odors, especially from sulfur compounds (i.e. sulfur containing amino acids cysteine, methionine). The versatility of PLP-dependant bioreactions arises from its ability to covalently bind the substrate and then to function as an electrophilic catalyst, thereby stabilizing different types of carbanionic reaction intermediates, containing iminium salt structures. This article summarizes the influence of PLP on sensorically important aroma compounds in wine growing and wine processing.