Carbamate Nucleophiles Research Articles

Enantioselective Intermolecular Radical Amidation and Amination of Benzylic C-H Bonds via Dual Copper and Photocatalysis.

A method for direct access to enantioenriched benzylic amides and carbamate-protected primary benzylamines by C-H functionalization is reported. The C-H substrate is used as limiting reagent with only a small excess of the unactivated amide or carbamate nucleophile. The enantioselective intermolecular dehydrogenative C-N bond formation is enabled by a combination of a chiral copper catalyst, a photocatalyst, and an oxidant, and it takes place under mild conditions, which allow for a broad substrate scope. The method is compatible with late-stage C-H functionalization, and it provides easy access to 15 N-labeled amides and amines starting from cheap 15 NH4 Cl.

Enantioselective Intermolecular Radical Amidation and Amination of Benzylic C−H Bonds via Dual Copper and Photocatalysis

AbstractA method for direct access to enantioenriched benzylic amides and carbamate‐protected primary benzylamines by C−H functionalization is reported. The C−H substrate is used as limiting reagent with only a small excess of the unactivated amide or carbamate nucleophile. The enantioselective intermolecular dehydrogenative C−N bond formation is enabled by a combination of a chiral copper catalyst, a photocatalyst, and an oxidant, and it takes place under mild conditions, which allow for a broad substrate scope. The method is compatible with late‐stage C−H functionalization, and it provides easy access to 15N‐labeled amides and amines starting from cheap 15NH4Cl.

Design of a Photoredox Catalyst that Enables the Direct Synthesis of Carbamate-Protected Primary Amines via Photoinduced, Copper-CatalyzedN-Alkylation Reactions of Unactivated Secondary Halides

Despite the long history of SN2 reactions between nitrogen nucleophiles and alkyl electrophiles, many such substitution reactions remain out of reach. In recent years, efforts to develop transition-metal catalysts to address this deficiency have begun to emerge. In this report, we address the challenge of coupling a carbamate nucleophile with an unactivated secondary alkyl electrophile to generate a substituted carbamate, a process that has not been achieved effectively in the absence of a catalyst; the product carbamates can serve as useful intermediates in organic synthesis as well as bioactive compounds in their own right. Through the design and synthesis of a new copper-based photoredox catalyst, bearing a tridentate carbazolide/bisphosphine ligand, that can be activated upon irradiation by blue-LED lamps, we can achieve the coupling of a range of primary carbamates with unactivated secondary alkyl bromides at room temperature. Our mechanistic observations are consistent with the new copper complex serving its intended role as a photoredox catalyst, working in conjunction with a second copper complex that mediates C-N bond formation in an out-of-cage process.

ChemInform Abstract: Highly Enantioselective, Intermolecular Hydroamination of Allenyl Esters Catalyzed by Bifunctional Phosphinothioureas.

AbstractA highly regio‐ and enantioselective γ‐hydroamination of allenyl and propargyl esters with N‐methoxy carbamate nucleophiles is developed to yield α,β‐unsaturated γ‐amino acid esters products.

Highly enantioselective, intermolecular hydroamination of allenyl esters catalyzed by bifunctional phosphinothioureas.

Bifunctional phosphinothiourea catalysts have been developed successfully for the highly regio- and enantioselective γ-hydroamination of allenyl and propargyl esters with N-methoxy carbamate nucleophiles to yield α,β-unsaturated γ-amino acid ester products. In the case of propargyl ester substrates, the reaction proceeds through reversible phosphinothiourea-catalyzed isomerization to the corresponding allenyl ester. The high enantioselectivity of the process is attributed to a cooperative conjugate addition of a thiourea-bound carbamate anion to a vinyl phosphonium ion resulting from covalent activation of the allenyl ester substrate.

Sequential Electrophilic Trifluoromethanesulfanylation–Cyclization of Tryptamine Derivatives: Synthesis of C(3)-Trifluoromethanesulfanylated Hexahydropyrrolo[2,3-b]indoles

A practical and efficient synthesis of C(3)-trifluoromethanesulfanylated hexahydropyrrolo[2,3-b]indoles 5 from tryptamine derivatives was described. The features of this synthesis included electrophilic activation of C(3) of tryptamine derivatives with "CF(3)S(+)" and cascade ring cyclization by carbamate nucleophile attacking at C(2). Surprisingly, when Lewis acid (BF(3)·OEt(2)) was used as activator instead of proton acid (TsOH·H(2)O) for the electrophilic trifluoromethanesulfanylation of tryptamine derivatives, the uncyclized product 6 was formed preferentially. This sequential trifluoromethanesulfanylation-cyclization protocol was used to synthesize several pyrrolidinoindolinic alkaloid analogues. The cytotoxicity activities of these trifluoromethanesulfanylated alkaloid analogues were evaluated against three cancer cell lines (K562, HeLa, L929).

Striking AcOH Acceleration in Direct Intramolecular Allylic Amination Reactions

After submission of the paper describing the use of AcOH as a solvent to accelerate Pd/bis-sulfoxide catalyzed allylic CH amination processes to form oxazolidinones and oxazinanones, a paper appeared by M. C. White et al. on the use of N-nosyl carbamate nucleophiles to accelerate analogous transformations.1 The authors would like to bring this to the reader's attention.

Allylic C−H Amination for the Preparation of syn-1,3-Amino Alcohol Motifs

A highly selective and general Pd/sulfoxide-catalyzed allylic C-H amination reaction en route to syn-1,3-amino alcohol motifs is reported. Key to achieving this reactivity under mild conditions is the use of electron-deficient N-nosyl carbamate nucleophiles that are thought to promote functionalization by furnishing higher concentrations of anionic species in situ. The reaction is shown to be orthogonal to classical C-C bond-forming/-reduction sequences as well as nitrene-based C-H amination methods.

The Reaction Mechanism of the Hydroamination of Alkenes Catalyzed by Gold(I)−Phosphine: The Role of the Counterion and the N-Nucleophile Substituents in the Proton-Transfer Step

The reaction mechanism of the gold(I)-phosphine-catalyzed hydroamination of 1,3-dienes was analyzed by means of density functional methods combined with polarizable continuum models. Several mechanistic pathways for the reaction were considered and evaluated. It was found that the most favorable series of reaction steps include the ligand substitution reaction in the catalytically active Ph3PAuOTf species between the triflate and the substrate, subsequent nucleophile attack of the N-nucleophile (benzyl carbamate) on the activated double bond, which is followed by proton transfer from the NH2 group to the unsaturated carbon atom. The latter step, the most striking one, was analyzed in detail, and a novel pathway involving tautomerization of benzyl carbamate nucleophile assisted by triflate anion acting as a proton shuttle was characterized by the lowest barrier, which is consistent with experimental findings.

Derailing the Wacker oxidation: development of a palladium-catalyzed amidation reaction.

[figure: see text] A conceptually new palladium-catalyzed amidation reaction is described for the synthesis of beta-amido ketones based on derailing the Wacker oxidation of enones. This reaction generates a new carbon-nitrogen bond via a palladium-catalyzed conjugate addition of a carbamate nucleophile to an enone. The regiocontrol, mild and neutral conditions, lack of preactivation of the nucleophile, and lack of reoxidation system for the catalyst are attractive features of this transformation.