Alkylation of N,N-Dibenzylaminoacetonitrile: From Five- to Seven-Membered Nitrogen-Containing Heterocyclic Systems

The syntheses of several alkaloids and nitrogen-containing compounds including N-Boc-coniine (14b), pyrrolizidine (1), δ-coniceine (2), and pyrrolo[1,2a]azepine (3) are described. New C-C bonds in the α position relative to the nitrogen atom were formed by the alkylation of metalated α-aminonitriles 4 and 6a-c with alkyl iodides possessing the requisite size and functionality. In all of the reported cases, the pyrrolidine ring was formed in the aqueous medium through a favorable 5-exo-tet process involving a primary or a secondary amino group and a terminal δ-leaving group. Conversely, the azepane ring was efficiently formed in N,N-dimethylformamide (DMF), as the preferred aprotic solvent, through an unreported 7-exo-tet cyclization process involving a more nucleophilic sodium amide and a terminal mesylate borne by a saturated six carbon chain unit. In this way, we successfully synthesized pyrrolo[1,2a]azepane 3 and 2-propyl-azepane 14c in good yields from inexpensive and readily available materials without tedious separation methods.