Palladium(II)-Catalyzed Intramolecular Aminocarbonylation of endo-Carbamates under Wacker-Type Conditions

Abstract

Pd(II)-catalyzed intramolecular aminocarbonylation of olefins bearing many types of nitrogen nucleophiles has been examined under two typical conditions: acidic conditions [conditions A, typically PdCl(2) (0.1 equiv) and CuCl(2) (3.0 equiv) under 1 atm of CO at room temperature in methanol] and buffered conditions [conditions B, typically PdCl(2) (0.1 equiv) and CuCl(2) (2.3 equiv) under 1 atm of CO at 30 degrees C in trimethyl orthoacetate]. Among nitrogen nucleophiles, endo-carbamates 7 display distinctive reactivity: endo-carbamates 7a-k smoothly undergo intramolecular aminocarbonylation under conditions B to furnish 4-[(methoxycarbonyl)methyl]-2-oxazolidinones 8a-k in good yields, while they would not undergo the expected reaction under conditions A. Other nitrogen nucleophiles (exo-ureas 1, endo-ureas 3, exo-carbamates 5, and exo-tosylamides 9), on the other hand, satisfactorily undergo aminocarbonylation only under conditions A to give rise to 2, 4, 6, and 10, respectively, in good yields. Under conditions B, they are unreactive and provide either the expected products in poor yields or intractable mixtures of products. On the basis of this contrasting reactivity between endo-carbamates and other nitrogen nucleophiles, the chemoselective aminocarbonylation of 7l-o has been achieved; aminocarbonylation takes place at the endo-carbamate moieties to furnish 8l-o exclusively under conditions B, and aminocarbonylation occurs at the exo-carbamate, exo-urea, and exo-tosylamide moieties to yield 13a-d exclusively under conditions A.

Palladium-catalyzed approach to the synthesis of five-membered O-heterocycles

“…This suggests that intramolecular carbopalladation (Pd-C bond insertion) is slow relative to the rate of Pd-alkoxide formation and oxypalladation (Pd-O bond insertion) under the reactions conditions described above (Scheme 44) [102]. In contrast to all previously described intermolecular carboetherification reactions of internal alkenes with aryl bromides [103,104], which provide syn-addition products, the intramolecular carboetherifications provide products resulting from anti-addition when chelating ligands with small bite angles (e.g., BINAP or DPPbenzene) are employed. It was previously shown that anti-addition products observed in intramolecular carboetherification reactions are actually generated through syn-oxypalladation followed by reversible β-hydride elimination/reinsertion/σ-bond rotation processes.…”

Palladium‐Catalyzed Oxidative Carbonylation Reactions

“…They also succeeded in finding optimal conditions for the oxidative carbonylation of 3‐hydroxypent‐4‐enylamides to produce the corresponding 3‐hydroxy pyrrolidine 2‐acetic acid lactones in 66–90 % of yields 28b. The same group also employed substituted ureas, 3‐hydroxy‐4‐pentenylamines, 4‐hydroxy‐5‐hexenylamines, 3‐buten‐1‐ols, 3‐butyn‐1‐ols, unsaturated carbamates, unsaturated amides, and even dienyl carbamates as substrates (Scheme ) 28c–j. The related oxidative carbonylation of allenic amides/amines for the synthesis of heterocyclic acrylates were described by Gallagher and co‐workers 29…”

A Cross-Metathesis/Aza-Michael Reaction Strategy for the Synthesis of Cyclic and Bicyclic Ureas

“…Given the significance of cyclic ureas, many synthetic strategies have been developed to generate these molecules . However, very few of these strategies effect both formation of the ring and a carbon–carbon bond in a single one-flask operation …”