Preferred Equatorial Linkages of Hexahydropyrimidine Rings in Dodecahydro-2,2'-bipyrimidines

Abstract

An X-ray crystallographic study of two new dodecahydro-2,2°-bipyrimidines, prepared from condensation of meso-pentane-2,4-diamine and racemic butane-1,3-diamine with glyoxal , has been carried out, The study demonstrates for the first time that the heterocyclic rings in such underivatized dodecahydrobipyrimidines exist in chair conformations with the bond bridging the two rings arranged equatorially to both. The methyl substituents in each case lie trans to the hydrogens at C2 and C2′ and the more crystalline isomer from the butanediamine precursor is derived from combination of amines of opposite configuration.