Current Organic Chemistry - Volume 25, Issue 19, 2021

1,4-Naphthoquinones are a group of natural and synthetic substances that participate in various biochemical functions in most plants and animals, being involved in energy production, electron transport, blood coagulation, and generation of reactive oxygen species (ROS), among others. The performance of such biochemical functions is directly related to the functional groups linked to the 1,4-naphthoquinone scaffold, and the introduction of nitrogencontaining groups into this nucleus may amplify its biological activity against numerous targets. Therefore, several methods have been developed in the last decades for preparing these compounds, especially from 1,4-naphthoquinone derivatives. Considering these concepts, in this review, we aim to provide insights into the chemistry, chemical synthesis, semi-synthesis, pharmacological effects, and reactivity of low molecular weight mono- and bis(aminonaphthoquinones); we start by discussing the use of some of the most important 1,4-naphthoquinones as starting materials for the synthesis of amino-1,4-naphthoquinones (ANQs), examine the modification of ANQ derivatives, and conclude by providing an outlook on this field.

The asymmetric reduction of oximes and hydrazones is an attractive and versatile strategy for the synthesis of chiral amines, which are valuable building blocks in organic synthesis. This review summarizes the relevant developments made in the last decade on the enantioselective and diastereoselective reduction of oximes and hydrazones involving metalcatalyzed hydrogenation/hydrogenolysis reactions, hydride donor reactions, and electrochemical reactions.

In the past few years, the number of protocols for α-amination of carbonyl compounds has dramatically increased, highlighting the importance of this moiety. While some classical approaches continue to be used, supported by novel catalysts, new methods with unique advantages have also emerged. Among these, a wide variety of conditions can be observed, such as the use of umpoled enolates with nucleophilic nitrogen sources, the generation of electrophilic nitrogen sources, and oxidative methods, generally through the generation of radical species. This review aims to compile the most recent publications for the α-amination of carbonyls on the basis of synthetic utility, novel transformations, and enantioselectivity.

An overview of the current uptake of continuous flow techniques for various functional group interconversion reactions is presented. Besides highlighting a variety of prominent examples and their main features, this review provides insights into specific reaction classes, such as oxidations, reductions, rearrangements as well as different C-H functionalization processes. While this review can only include key examples from the last decade, the reader will find a solid foundation of important transformations along with further references to inform and appreciate the opportunities arising from modern synthesis technologies such as flow synthesis.

The metal-mediated formation of heterocycles is one of the most emerging and important strategies in organic chemistry. The reactions utilized previously for the synthesis of heterocycles were less familiar to the scientists due to their complicated work-up, expensive nature, and difficult operations. The silver-assisted cyclic reactions are highly efficient for both regioselective and stereoselective syntheses of five-membered fused N-heterocyclic compounds. The applications of silver in the preparation of five-membered fused N-heterocyclic compounds are covered in this review article.