Chemoselective and Triggered Decomposition of Diazo Esters by the [(IMes)Rh2(OAc)4] Complex: En Route to Assisted Tandem Catalysis from Mixtures of Diazo Compounds

• Published in: European journal of organic chemistry 2024-09, Vol.27 (34), p.n/a
• Main Authors: Hammoud, Jana, Gandon, Vincent, Joosten, Antoine Y. P., Lecourt, Thomas
• Format: Article
• Language: English
• Subjects: Carbenes; Carbenoids; Cascade reactions; Catalysis; Catalytic activity; Chemoselectivity; Chloroform; Decomposition; Decomposition reactions; Diazo compounds; Esters; Extrusion rate; Gallium chloride; Insertion; Mixtures; Nitrogen; Rhodium; Room temperature; Substrates
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202400555

Decomposition of aryl and unsubstituted diazo ester into Rh(II)‐carbenes by the [(IMes)Rh2(OAc)4] complex is shown to be slower than with Rh2(OAc)4. Diazo esters substituted by a second electron‐withdrawing group do not suffer nitrogen extrusion when exposed for several hours to this (NHC)Rh(II) complex at room temperature. This chemoselective decomposition of diazo esters depending on their substituent (Ar, H, EWG) can furthermore be achieved on a mixture of substrates. The catalytic activity of [(IMes)Rh2(OAc)4] towards electron‐poor diazo compounds is also restored by heating to reflux in chloroform, or after decomplexation of the NHC by addition of GaCl3. The [(IMes)Rh2(OAc)4] complex was then used to induce a fully selective reaction cascade from a mixture of two diazo esters. First, a donor/acceptor diazo compound was decomposed selectively at room temperature to give an intermolecular O−H insertion product without any decomposition of the electron poor diazo compound. Addition of GaGl3 then triggered nitrogen extrusion from the diazo malonate to give a 1,5‐C−H insertion product. This transformation, where decomposition of diazo compounds catalyzed by Rh(II) complexes can be externally controlled, represents the first example of assisted tandem catalysis with two metal carbene precursors. Start and stop: electron poor diazo compounds cannot give rise to carbene‐mediated transformations at room temperature under [(IMes)Rh2(OAc)4] catalysis but their reactivity can be restored on demand by external stimuli (heat or addition of a Lewis acid).