Chemoselective Allene Aziridination via Ag(I) Catalysis

Abstract

Allene aziridination generates useful bicyclic methylene aziridine scaffolds that can be flexibly transformed into a range of stereochemically complex and densely functionalized amine-containing stereotriads. The scope of this chemistry has been limited by the poor chemoselectivity that often results when typical dinuclear Rh(II) catalysts are employed with homoallenic carbamates. Herein, Ag(I) catalysts that significantly improve the scope and yield of bicyclic methylene aziridines that can be prepared via allene aziridination are described.

Tunable, Chemoselective Amination via Silver Catalysis

“…6,7a–f However, a tridentate ligand reversed this selectivity (entries 8 and 16). This result stimulated our curiosity, and a further perusal of the literature showed that Ag has the unique ability to change coordination geometry in response to changes in the Ag counteranion, the ligand identity, or the metal/ligand ratio.…”

Chemoselective silver-catalyzed nitrene insertion reactions

“…Aziridine yields using the less expensive AgOTf/phen catalyst system were high for all substrates studied [14]. After establishing the aziridination activity of these catalysts, 4 Proposed mechanism for Ag(I)-catalyzed amination of alkenes invoking nitrene intermediates [13].…”

“…Simultaneously with the mechanistic studies described by Perez, the Schomaker group applied silver(I) catalysis to the intramolecular aziridination of homoallenic and homoallylic carbamates [14][15][16]. Schomaker found that typical dinuclear Rh(II) catalysts for nitrene insertion gave poor chemoselectivity and limited substrate scope in the amination of homoallenic carbamates 7a and 7b (Table 3, entries 1-2 and 6-7).…”

“…Brought to you by | Cornell University Library Authenticated Download Date | 6/24/15 11:12 PM Table 4 Aziridination of homoallenic carbamates [14]. chemoselectivity was explored with homoallenic carbamates containing C-H insertion sites that would compete for nitrene insertion with the allene double bond.…”

“…The Schomaker group has recently described an interesting solution to this problem by harnessing the unique ability of silver complexes to adopt different coordination geometries in response to minor changes in the reaction conditions (Table 6) [18]. A simple change in the metal:ligand ratio diverts the reaction pathway to favor either aziridination or C-H insertion [14,15]. These complementary Ag(I) catalyst systems employ AgOTf as the silver source and 1,10-phenanthroline (phen) as the ligand.…”