An efficient synthetic process for chiral tetraamine base (R,R)-5 is reported that leverages mechanistic understanding to enable control over key transformations. Specifically, a configurationally stable and observable aziridinium ion intermediate was found to undergo counterion exchange impacting the feasibility of the process. Mechanistic investigations revealed that both counterion exchange and trapping of the aziridinium ion were biphasic events and that the former could be suppressed at lower temperatures, facilitating the reaction on both small and large scales. The mechanistic insights gained have led to the development of an efficient one-pot process that enables preparation of multiple kilograms of (R,R)-5 as a crystalline solid without chromatography in excellent chemical and chiral purity.

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Base. -The dilithiated amine CDA is found to control the regioand stereoselectivity of the title reaction. The pharmaceutically interesting products include the potential type-2 diabetes therapeutic agent AMG 221 (VII) with good de. -(FRIZZLE, M. J.; NANI, R. R.; MARTINELLI, M. J.; MONIZ*, G. A.; Tetrahedron Lett. 52 (2011) 43, 5613-5616, http://dx.