The Dimroth rearrangement. XVII. The rearrangement of some 1,6-Dihydro-6-imino-1,2-polymethylenepyrimidines into 2,N⁶-polymethylene-bridged 6-aminopyrimidines

Abstract

The cyclic imino ether, 2-ethoxy-3,4,5,6,7,8-hexahydroazocine (4; n = 6), condenses with amino-methylenemalononitrile (3; R = CN) to give the bicyclic imine, 6,7,8,9,10,11-hexahydro-4-imino-4H-pyrimido[1,2- alazocine-3-carbonitrile (5f), which undergoes Dimroth rearrangement in boiling butanol to yield a β-bridged isomer, 2,10,13- triazabicyclo[7,3,1]trideca-1(13),9,11-triene-12-carbo-nitrile (7a). Imino ethers (4) with fewer than six methylene groups give bicyclic imines which are incapable of rearrangement; those with more than six methylene groups give imines which cannot be isolated on account of their extremely facile rearrangement into β-bridged isomers. Ionization constants and the ultraviolet, infrared, proton magnetic resonance and mass spectra of the main products are discussed.