Acid-catalysed rearrangements between 3,4-dihydro-2H-1,5-benzooxazocine and -benzothiazocine and their macrocyclic (16-membered, 24-membered and 32-membered) oligomers

Abstract

Treatment of 2-(3-azidopropoxy)benzaldehyde with triphenylphosphine in diethyl ether, followed by sequestration of the products with nickel(II) thiocyanate and subsequent liberation from the complex with aqueous ammonia, produces the 16-membered dimer of 3,4-dihydro-2H-1,5-benzooxazocine. The dioxadiaza diimine macrocycle 3 undergoes an acid-catalysed rearrangement in solution into an equilibrium mixture that includes the trioxatriaza triimine (24-membered) 8 and tetraoxatetraaza tetraimine (32-membered) 9 macrocycles, as well as the diimine. The oligomers in [²H]chloroform differ in the ¹H NMR chemical shifts of the protons on the central carbon atoms of the propane-1,3-diyl links, thereby allowing an investigation of the factors involved in the rearrangements between the macrocyclic oligomers. Thus, the rearrangements of the macrocyclic polyimines into equilibrium mixtures of the various oligomers occurs with t>>½>> 7–10 min, but the position of the equilibrium in each case is dependent upon the imine equivalent concentration of the solution. 3,4-Dihydro-2H-1,5-benzothiazocine undergoes a similar rearrangement. The equilibrations have been ascribed to facile intermolecular transiminations between the oligomers in the presence of traces of acid and to the similarities of the thermodynamic stabilities of the 16-, 24- and 32-membered oligomers. The crystal and molecular structures of ammonium nitrate salts of the 16-membered diamine 11 and 32-membered tetraamine 10 derivatives of the corresponding macrocyclic benzooxazocines are reported.