Urotropine isomer (1,4,6,10-tetraazaadamantane): synthesis, structure, and chemistry

The first synthesis of 1,4,6,10-tetraazaadamantane, the C3v-symmetrical structural isomer of urotropine (1,3,5,7-tetraazaadamantane), and a series of its derivatives is reported. X-ray and quantum-chemical studies revealed remarkable distinctions in structures of urotropine and "isourotropine" cations, probably arising from different types of hyperconjugation between lone electron pairs of nitrogen atoms and σ*C-N orbitals in these heterocage systems. Since substitution at bridge and bridgehead nitrogen atoms can be easily introduced, 1,4,6,10-tetraazaadamantane may be considered as a new rigid multivalent (3 + 1) scaffold for the design of functional molecules and materials.