Supercritical Carbon Dioxide as Solvent and Temporary Protecting Group for Rhodium-Catalyzed Hydroaminomethylation

Abstract

Supercritical carbon dioxide (scCO2) acts simultaneously as solvent and temporary protecting group during homogeneously rhodium-catalyzed hydroaminomethylation of ethyl methallylic amine. Cyclic amines are formed as the major products in scCO,, whereas the cyclic amide is formed preferentially in conventional solvents. Multinuclear high-pressure NMR spectroscopy revealed that this selectivity switch is mainly due to reversible formation of the carbamic acid in the solvent CO2, which reduces the tendency for intramolecular ring closure at the Rh-acyl intermediate. These results substantiate the general concept of using scCO2 as a protective medium for amines in homogeneous catalysis and demonstrate for the first time its application for selectivity control.

Selective chemical reactions in supercritical carbon dioxide, water, and ionic liquids

“…Intramolecular hydroaminomethylation of an unprotected secondary allylic amine Leitner and co-workers reported (53) an efficient intramolecular hydroaminomethylation of an unprotected secondary allylic amine using 1 mol% of Rh catalyst and fluorinated phosphine ligand in scCO 2 . In this case the scCO 2 was used as a temporary protecting group as well as sustainable solvent.…”

Supercritical and Compressed Carbon Dioxide as Reaction Medium and Mass Separating Agent for Hydrogenation Reactions using Organometallic Catalysts

“…The application of the rhodium-based catalytic system for this reaction under scCO 2 conditions was made possible by the use of the CO 2 -philic derivative of triphenylphosphine 9 [24]. Under conventional conditions, path B is preferred, leading to pyrrolidone 12 as the major product.…”

Chemische Synthese in überkritischem Kohlendioxid: Die „bessere Lösung”︁?

“…In analoger Weise bilden basische Amine sogenannte Carbaminsäuren, was sich zur Verwendung von scCO 2 als Lösungsmittel und in-situ-Schutzgruppe ausnutzen lässt. Dieses allgemein gültige Prinzip [15] soll erneut anhand der Olefinmetathese illustriert werden (Abbildung 7). Der Rutheniumkatalysator wird durch die Aminfunktion irreversibel deaktiviert, und die Zyklisierung erfordert in konventionellen Lösungsmitteln drei getrennte Syntheseschritte: Schutzgruppe einführen, Olefinmetathese, Schutzgruppe abspalten.…”