Vicinal diamines are ubiquitous functional motifs across many disciplines of chemistry. The presence of 1,2-diamine moieties in natural products, pharmaceutical compounds, and ligands has inspired efforts to design methods for the preparation of these structures from simple precursors such as alkenes. However, the introduction of two amino groups across the double bond has been more difficult to accomplish compared to the analogous dihydroxylation or aminohydroxylation of alkenes. In this work, we described two different, but related methods using simple and easily accessible reagents for syn 1,2-diamination of alkenes. In the first method (Scheme 1, method A), the alkene undergoes 1,3-dipolar cycloaddition with an organic azide to form a 1,2,3-triazoline. Subsequent N-alkylation of the generated 1,2,3-triazoline gives the 1,2,3-triazolinium ion, which we then hydrogenate over Raney Ni with a balloon of H2 at room temperature to excise the middle N atom and produce a 1,2-diamine. (Traditionally, it has been believed that a 1,2,3-triazoline is an unstable species that will readily extrude N2 in the presence of heat or light to form an imine or aziridine. However, most of the 1,2,3-triazolines that we prepared were stable to the extrusion of N2 at the temperature required for their formation.) In the second method (Scheme 1, method B), the alkene undergoes 1,3-dipolar cycloaddition with a 1,3-diaza-2-azoniaallene (azidium ion, ArN=N+=NAr) to afford a 1,2,3-triazolinium ion directly. The 1,2,3-triazolinium ions are reduced to the corresponding 1,2-diamines using the same conditions described above. X-ray crystallography confirmed stereospecific syn 1,2-diamination of alkenes in this method.

Syn 1,2-diamination of alkenes via reduction of 1,2,3-triazolinium ions

ACS Fall 2021

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