Diels-Alder reactions of 3,6-disubstituted 1,2,4,5-tetrazines. Synthesis and X-ray crystal structures of diazafluoranthene derivatives

Abstract

The synthesis of a series of 3,6-disubstituted-1,2,4,5-tetrazines has been effected using an inverse electron demand [2 + 4] cycloaddition strategy. The crystal structures of 18 members of this series of diazafluoranthenes are reported. Stereochemical analysis shows that diazafluoranthenes, substituted across the bay region, are helically-twisted strained aromatic molecules. The dihedral angle between pyridazyl vs naphthyl rings ranges from 0.5° to 20.9°, and follows the degree of steric congestion in the bay region. The crystal structures are compared to computational structures determined using density functional theory, with the M06-2X/cc-pVDZ method. © 2009 The Royal Society of Chemistry.