| Abstract: | Vinylogous Acyl Compounds. XVIII. Influence of Steric Factors on the Reaction Behaviour of Vinylogous Carbonamidium Salts Depending on the size of their N-alkyl groups vinylogous carbonamidium salts show a markedly graduated reactivity under suitable conditions. Thus 2-formyl-vinyl trimethylammonium perchlorate 1a is decomposed by sodium hydroxide yielding only trimethylamine and salts of malondialdehyde 2 , while the analogous triethylammonium salt 1b additionally undergoes a fragmentation to triethylamine, acetylene and formic acid. The reaction of 4-(4-nitrobenzyl)-pyridine with 1 and the analogous 2-benzoylvinylammonium salts 3 to the 1,4-dihydropyridine dye 4 and 5 , respectively, is faster by orders of magnitude in the case R′ = CH3 than in the case R′ = C2H5. Contrary to the 1a -p-nitrophenylhydrazone 6a which can be transformed into the pyrazole 7 the 1b -hydrazone 6b withstands such a ring closure. Depending on the reaction conditions and nature of the substituent R the action of aniline on 1 leads either to the monoanils 8 or to the malondialdehyde dianil salt 9 . While piperidine reacts with 3a as well as with 3b to give N-(2-benzoylvinyl)-piperidine 10 , aniline forms a corresponding vinylogous amide 11 only with 3a. 3b , however, on reaction with aniline · HCl via the intermediate monoanil 12 , yields the vinylogous amidinium salt 13 which is not obtainable from 3a or 11 . Using o-phenylendiamine this reactivity graduation can be utilized for preparing 2-aryl-substituted 1H-1,5-benzodiazepinium salts, e.g. 17 . |
