Rare-Earth-Metal-Complex-Catalyzed Hydroalkoxylation and Tandem Hydroalkoxylation/Cyclohydroamination of Isocyanates: Synthesis of Carbamates and Oxazolidinones

Abstract

Novel N,N,N-tridentate β-diketiminato rare-earth-metal dialkyl complexes LRE­(CH2SiMe3)2 [RE = Y (1a), Gd (1b), Yb (1c), Lu (1d); L = MeC­(NDipp)­CHC­(Me)­N­(CH2)2NC4H8, where Dipp = 2,6- i Pr2C6H3] have been conveniently synthesized by one step from reactions of the rare-earth-metal trialkyl complexes RE­(CH2SiMe3)3(THF)2 (THF = tetrahydrofuran) with a pyrrolidine-functionalized β-diketiminate HL, and their catalytic behaviors toward hydroalkoxylation and tandem hydroalkoxylation/cyclohydroamination of isocyanates have been described. These rare-earth-metal catalysts exhibited high efficiency in the hydroalkoxylation of isocyanates, providing a variety of N-alkyl and N-aryl carbamate derivatives under mild reaction conditions with a rather low catalyst loading (0.04 mol %). More significantly, they can promote a tandem hydroalkoxylation/cyclohydroamination reaction between terminal and internal propargylic alcohols with substituted arylisocyanates, leading to the efficient synthesis of methylene and (Z)-selective arylidene oxazolidinones in good-to-high yields via consecutive C–O and C–N bond formation. The stoichiometric reaction of 1a with p-tolylisocyanate generated an unusual dinuclear yttrium complex, {[η2-(4-MePhNCO)­(CH2SiMe3)]­Y­[μ-η2:η1:η1-(4-MePhNCO)­CC­(Me)­(NDipp)­C­(Me)­N­(CH2)2NC4H8]}2 (7a), with two different amidate units, which underwent an sp2 C–H bond activation of the β-diketiminato backbone, followed by the insertion of isocyanate.

Lanthanide Mimicking by Magnesium for Oxazolidinone Synthesis

“…This reflects that the substitution on the aromatic ring of isocyanates has a noticeable influence on the reaction outcome. Wang and coworkers reported that their Sc‐catalyst does not work for nitro‐substituted phenyl isocyanate, [12] but our catalyst works very well for 3‐nitro phenyl isocyanate (see Scheme 6, 6 i ). Surprisingly, in the case of 6 k , multiple products also form even after 30 h of reaction time.…”

“…These methods predominantly employ transition metal-based catalysts like Ir, Pd, or coinage metals, lanthanides. [7][8][9][10][11][12][13] The interest in developing environmentally friendly and safer synthesis methods for industrial processes is steadily increasing. The abundant presence of magnesium in the Earth's crust has led to a surge in research on its application in catalytic processes, with notable contributions from research groups such as Harder, Hill,Parkin,Okuda,Rueping,Milstein,Sadow,Schäfer,Pucheault,Nembenna,Venugopal, Despite the growing use of magnesium complexes in catalysis over the past decade, their utilization has primarily been limited to hydrofunctionalization reactions involving unsaturated bonds like aldehydes, ketones, alkenes, alkynes, carbodiimides, and isocyanates.…”

“…Additional methods, such as amide activation, cyclization of 2‐vinyl aziridines, intermolecular aminohydroxylation, and carbonylation of propargylic amines, have been reported. These methods predominantly employ transition metal‐based catalysts like Ir, Pd, or coinage metals, lanthanides [7–13] …”

Access to Amides and Lactams via Pyridotriazole as a Transformable Directing Group

“…Amide and lactam scaffolds are a class of substantial motifs frequently found in pharmaceuticals and naturally occurring molecules like imatinib, lenalidomide, and elmenol H. − A wide range of approaches to constructing such indispensable amide bonds have been developed, ranging from conventional acylation of amines mediated by amide coupling agents , to modern strategies such as catalytic direct amidation , or visible light irradiation. , Among these studies, transition-metal-catalyzed C–H activation stands out as a simpler synthetic route for direct amidation of unactivated C–H bonds. − Many transition-metal-catalyzed C–H functionalization methods require directing groups (DGs), − especially transformable DGs, to enhance the regioselectivity and practicality. − By the DG-assisted C–H activation strategy, selectively installing nitrogen-based functional groups (FGs) into molecules via the direct addition of C–H bonds to unsaturated polar C–N π-bonds represents the most powerful and economical method for rapid amide and lactam synthesis. − We envisioned isocyanates to be particularly useful. As useful carbon synthons in organic synthesis, isocyanates have been extensively implemented in the construction of C–C bond formation for forging amides. − Hence, employing isocyanates as FGs would be a more straightforward approach to the synthesis of amides.…”

Hydrolysis of a carbamate triggered by coordination of metal ions

“…The chemistry of carbamates has been intensively studied in the last few years. [1][2][3] The interest in this type of system lies in a wide variety of applications in fields as different as medicinal chemistry 4,5 or new environmentally related materials. 3 Thus, the capture of CO 2 using ligands with amino groups that give rise to carbamates can be highlighted as a methodology for reducing greenhouse gas emissions.…”