Synthetic route towards 1,2,3,4-tetrahydroquinoxaline/piperidine combined tricyclic ring system

Abstract

The synthetic route toward novel tricyclic, nitrogen-containing sys-tem is disclosed. Three novel compounds possessing structural features of 1,2,3,4-tetrahydroquinoxaline and decahydropyrido[3,4-b]pyrazine are synthe-sized starting from readily available precursors in six or seven steps, of which the last three or four steps respectively are diastereoselective. Key reaction steps include N-acylation, Hofmann rearrangement and ring-closing Buch-wald?Hartwig reaction. Compounds trans-8, cis-12 and trans-12 are synthe-sized in order to prove that this novel, tricyclic system can be functionalized with various groups. Synthetic significance of this heterocyclic system lies in the possibility for the orthogonal functionalization of three different amino groups, allowing fine structural tuning.