Mechanism of formation and stabilities of the new dioxadiazadecalin systems. Ring-chain tautomerism

A linear free energy relationship study is presented for the reactions of t hreo- and erythro-1,4-diamino- and -2,3-diaminobutanediols (1, 2) with six p-substituted benzaldehydes, the end products of which are the novel cis- a nd trans-1,5-dioxa-3,7-diazadecalin (DODAD, 7ci, 7tr) and -1,5-diaza-3,7-di oxadecalin (DADOD, 8ci, 8tr) systems. The consecutive double 1,3-oxazane ri ng closures take place mostly via Schiff bases and are moderately polar rin g-chain tautomeric reactions with low positive rho-values (0.69) affected b y steric strain, stereoelectronic effects, and intramolecular hydrogen bond s. These are relatively slow processes, which may occur in the solid as wel l, but are greatly enhanced by acid catalysis.