Arbeiten über Phosphorsäure‐ und Thiophosphorsäureester mit einem heterocyclischen Substituenten. 8. Mitteilung . Das Stäubli ‐Verfahren, eine Eintopf‐Kondensation von Thiophosphorverbindungen (, XO,S), Aldehyden und Heterocyclen (mit saurer NH‐Gruppe)

The condensation reaction of thiophosphoric compounds 1 , aldehydes and heterocycles 3 with an acidic NH‐group in strong mineral acid of specific concentration to asymmetrical compounds 4 , called Stäubli procedure, differs from the Mannich ‐type reaction catalyzed by weak or dilute acid (aminoalkylation of Hellmann & Opitz ) and from the Tscherniac‐Einhorn ‐type condensation in concentrated sulfuric acid (amidomethylation of Hellmann ). Its main feature is the acidity of the two condensation participants 1 and 3 ; therefore an attuned concentration of mineral acid is required to activate them each to its individual optimum extent. Their p K difference, however, is sufficient to differentiate their nucleophility and reactivity and to prevent a simultaneous reaction of both of them with the aldehyde provocating side reactions to symmetrical by‐products such as 13, 14 and 15 .