Pursuing effective Gram-negative antibiotics: The chemical synthesis of negamycin

The Development of a Sulfamate-Tethered Aza-Michael Cyclization Allows for the Preparation of (-)-Negamycin tert-Butyl Ester

We present the first examples of intramolecular aza-Michael cyclizations of sulfamates and sulfamides onto pendant α,β-unsaturated esters, thioesters, amides, and nitriles. Stirring the substrate with catalytic quantities of the appropriate base delivers the product in good yield and excellent diastereoselectivity. The reactions are operationally simple, can be performed open to air, and are tolerant of a variety of important functional groups. We highlight the utility of this technology by using it in the preparation of a (-)-negamycin derivative.

Photoredox-Catalyzed Hydroacylation of Azobenzenes with Carboxylic Acids

Acyl hydrazides are widely found in bioactive compounds and have important applications as versatile synthetic intermediates. In the current report, a photoredox-catalyzed hydroacylation of azobenzenes was disclosed with carboxylic acids as the acylation reagent, affording a variety of N,N'-disubstituted hydrazides. The process possesses the advantages of mild reaction conditions, broad substrate scope, and high efficiency. Preliminary mechanistic investigation indicated that the addition of an acyl radical to the azo compound should be involved.

Silver-Catalyzed Enantioselective Propargylic C-H Bond Amination through Rational Ligand Design

Asymmetric C-H amination via nitrene transfer is a powerful tool to prepare enantioenriched amine precursors from abundant C-H bonds. Herein, we report a regio- and enantioselective synthesis of γ-alkynyl γ-aminoalcohols via a silver-catalyzed propargylic C-H amination. The protocol was enabled by a new bis(oxazoline) (BOX) ligand designed via a rapid structure-activity relationship (SAR) analysis. The method utilizes accessible carbamate esters bearing γ-propargylic C-H bonds and furnishes versatile products in good yields and excellent enantioselectivity (90-99% ee). The putative Ag-nitrene is proposed to undergo enantiodetermining hydrogen-atom transfer (HAT) during the C-H amination event. Density functional theory calculations shed insight into the origin of enantioselectivity in the HAT step.