CuCl-catalyzed radical cyclisation of N-α-perchloroacyl-ketene-N,S-acetals: a new way to prepare disubstituted maleic anhydrides

Modern Synthesis and Chemistry of Stabilized Ketene N,O-Acetals

Ketene N,O-acetals are robust and versatile synthons. Herein, we outline the synthesis of stable ketene N,O-acetals in the twenty-first century. In addition, we review recent developments in the chemistry of ketene N,O-acetals, as it applies to the vinylogous Mukaiyama aldol reaction, electrolysis, and pericyclic transformations. While dated reports rely on in situ use, modern methods of ketene N,O-acetal synthesis are heavily oriented towards producing products with high ‘bench’ stability; moreover, in the present century, chemists typically enhance the stability of ketene N,O-acetals by positioning an electron-withdrawing group at the β-terminus or at the N-position. As propitious substrates in the vinylogous Mukaiyama aldol reaction, ketene N,O-acetals readily provide polyketide adducts with high regioselectivity. When exposed to electrolysis conditions, the title functional group forms a reactive radical cation and cleanly couples with a variety of activated olefins. Given their electron-rich nature, ketene N,O-acetals act as facile substrates in several rearrangement reactions; further, ketene N,O-acetals reserve the ability to act as either dienophiles or dienes in Diels–Alder reactions. Lastly, ketene N,O-acetals are seemingly more stable than their O,O-counterparts and more reactive than analogous N,N- or S,S-acetals; these factors, in combination, make ketene N,O-acetals advantageous substitutes for other ketene acetal homologues.

1 Introduction

2 Select Methods of Stabilization-Oriented Ketene N,O-Acetal Synthesis

3 Ketene N,O-Acetals in the Vinylogous Mukaiyama Aldol Reaction

4 Ketene N,O-Acetals in Anodic Coupling and Electrochemical Oxidation Reactions

5 Rearrangement and Diels–Alder Reactions of Ketene N,O-Acetals

6 Conclusions, Perspectives, and Directions

Chemistry of Substituted Thiazinanes and Their Derivatives

Thiazinanes and its isomeric forms represent one of the most important heterocyclic compounds, and their derivatives represented a highly potent drug in disease treatment such as, 1,1-dioxido-1,2-thiazinan-1,6-naphthyridine, which has been shown to have anti-HIV activity by a mechanism that should work as anti-AIDS treatment, while (Z)-methyl 3-(naphthalen-1-ylimino)- 2-thia-4-azaspiro[5 5]undecane-4-carbodithioate showed analgesic activity, cephradine was used as antibiotic and chlormezanone was utilized as anticoagulants. All publications were interested in the chemistry of thiazine (partially or fully unsaturated heterocyclic six-membered ring containing nitrogen and sulfur), but no one was dealing with thiazinane itself which encouraged us to shed new light on these interesting heterocycles. This review was focused on the synthetic approaches of thiazinane derivatives and their chemical reactivity.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Novel route to chaetomellic acid A and analogues: serendipitous discovery of a more competent FTase inhibitor

A new practical route to chaetomellic acid A (ACA), based on the copper catalysed radical cyclization (RC) of (Z)-3-(2,2-dichloropropanoyl)-2-pentadecylidene-1,3-thiazinane, is described. Remarkably, the process entailed: (i) a one-pot preparation of the intermediate N-α-perchloroacyl-2-(Z)-alkyliden-1,3-thiazinanes starting from N-(3-hydroxypropyl)palmitamide, (ii) a two step smooth transformation of the RC products into ACA and (iii) only one intermediate chromatographic purification step. The method offers a versatile approach to the preparation of ACA analogues, through the synthesis of an intermediate maleic anhydride with a vinylic group at the end of the aliphatic tail, a function that can be transformed through a thiol-ene coupling. Serendipitously, the disodium salt of 2-(9-(butylthio)nonyl)-3-methylmaleic acid, that we prepared as a representative sulfurated ACA analogue, was a more competent FTase inhibitor than ACA. This behaviour was analysed by a molecular docking study.