Benzylamine-Free, Heavy-Metal-Free Synthesis of CL-20

Abstract : The main objective of this SERDP SEED project was to demonstrate the feasibility of preparing the hexaazaisowurtzitane cage in a form that is efficiently directly nitrolyzable to CL-20 without a requirement for expensive benzylamine starting material or heavy metals, including palladium, involved in its production. We applied a known chemical transformation, base-catalyzed isomerization of allylamines into 1-propenylamines, to the recently reported hexaallylhexaazaisowurtzitane to prepare hexa(1-propenyl)- hexaazaisowurtzitane (HPIW). We next performed photooxygenation of this intermediate, using singlet oxygen gas, in order to oxidize the 1-propenyl substituents to formyl substituents. Although the oxidation reaction did not go to completion to produce hexaformylhexaazaisowurtzitane, the partially oxidized product formed did undergo nitrolysis to form CL-20 in a clean reaction. Furthermore, we demonstrated that the new intermediate, HPIW, underwent direct nitrolysis to form CL-20, though initial conditions did not do so as cleanly as with its oxidation product as a precursor for nitrolysis.