Organocatalytic activation of hydrogen peroxide: towards green and sustainable oxidations

The advent of organocatalysis provided an additional option in every researcher's arsenal, towards the development of elegant and sustainable protocols for various organic transformations. Oxidation reactions are considered to be key in organic synthesis since oxygenated functionalities appear in many natural products. Hydrogen peroxide is categorized as a green oxidant, since its only by-product is water, offering novel opportunities for the development of green and sustainable protocols. In this review article, we intend to present recent developments in the field of the organocatalytic activation of hydrogen peroxide, providing useful insight into the applied oxidative protocols. At the same time, we will present some interesting mechanistic studies, providing information on the oxygen transfer processes.

Cu-Catalyzed Asymmetric Hydroboration of Naphthylallylic Compounds for Enantioselective Synthesis of Chiral Boronates

A Cu-catalyzed regio- and enantioselective hydroboration of various naphthylallylic compounds affording chiral boronates with high yields and excellent enantioselectivities (up to 96% ee) was presented. The utility of the boronated products is further illustrated by other stereospecific C-B bond transformations to produce amino alcohols and other useful compounds.

Green Organocatalytic Synthesis of Isoxazolines via a One-Pot Oxidation of Allyloximes

A green, sustainable, organocatalytic, and efficient synthesis of isoxazolines from allyloximes was developed. A 2,2,2-trifluoroacetophenone-catalyzed oxidation of allyloximes, utilizing H₂O₂ as the green oxidant, was taken advantage of in order to introduce a cheap and environmentally friendly protocol for the synthesis of substituted isoxazolines. A variety of substitution patterns, both aromatic and aliphatic moieties, are well tolerated, leading to isoxazolines in moderate to excellent yields.

Enantioselective Organocatalytic Synthesis of 2-Oxopiperazines from Aldehydes: Identification of the Elusive Epoxy Lactone Intermediate

An organocatalytic linchpin catalysis approach was envisaged to convert simple aldehydes into enantioenriched 2-oxopiperazines. A four-step reaction sequence (chlorination, oxidation, substitution, and cyclization) was developed and led to different substitution patterns in high yields and selectivities. The reaction mechanism was studied, and the previously elusive epoxy lactone intermediate was identified by HRMS.

Photoorganocatalytic One-Pot Synthesis of Hydroxamic Acids from Aldehydes

An efficient one-pot synthesis of hydroxamic acids from aldehydes and hydroxylamine is described. A fast, visible-light-mediated metal-free hydroacylation of dialkyl azodicarboxylates was used to develop the subsequent addition of hydroxylamine hydrochloride. A range of aliphatic and aromatic aldehydes were employed in this reaction to give hydroxamic acids in high to excellent yields. Application of the current methodology was demonstrated in the synthesis of the anticancer medicine vorinostat.

Green organocatalytic α-hydroxylation of ketones

An efficient and green method for the α-hydroxylation of substituted ketones has been developed.

N–O linkage in carbohydrates and glycoconjugates

The synthesis and chemical and physicochemical properties as well as biological and medical applications of various hydroxylamine-functionalized carbohydrate derivatives are summarized.

On the scope of oxidation of tertiary amines: Meisenheimer rearrangements versus Cope elimination in 2-(cyanoethyl)-2-azanorbornanes

When oxidized, exo-2-(cyanoethyl)-2-azanorbornene is prone to [1,2]-Meisenheimer rearrangement, its endo isomer undergoes [2,3]-Meisenheimer and exo/endo-2-(cyanoethyl)-2-azanorbornanes afford N-hydroxylamines through Cope elimination.