Transition metal-catalyzed C-C bond formations have been well studied over the last four decades. An improved mechanistic understanding of such reactions has helped chemists to develop further improvements, modifications and even new reactions. In the area of transition metal-catalyzed cross-coupling reactions the C-S bond cleaving reactions have attracted a lot of attention in the last decade as they provide a good alternative to the use of organo-halide reagents in traditional cross-coupling reactions. The availability of a wide range of organo-sulfur species provides the opportunity for developing different transformations for the synthesis of interesting organic compounds. This tutorial review focuses on recent examples of the transition metal-catalyzed C-C bond forming reactions using organo-sulfur species.
Cycloaddition reactions belong to one of the most well-investigated and widely used reactions in synthetic organic chemistry for the construction of (hetero)cyclic compounds in a single-step operation. In this tutorial review, a select number of examples of some [3+2] cycloadditions, i.e. for 1,2,3-triazole formation, as well as of some [4+2] and [2+2] cycloadditions are reviewed, where it has been proven that the application of microwave irradiation has a profound influence on the outcome of the reaction.
A simple protocol for the difluoromethylation of thiols is reported using chlorodifluoroacetate as the difluoromethylating agent. This cheap reagent undergoes smooth decarboxylation at 95 °C to afford difluorocarbene, which can be trapped with a variety of aromatic and heteroaromatic thiols. The reaction is also effective for the difluoromethylation of heterocyclic nitrogen compounds and phenylselenol.
Among the fundamental transformations in the field of synthetic organic chemistry, transition-metal-catalyzed reactions provide some of the most attractive methodologies for the formation of C-C and C-heteroatom bonds. As a result, the application of these reactions has increased tremendously during the past decades and cross-coupling reactions became a standard tool for synthetic organic chemists. Furthermore, a tremendous upsurge in the development of new catalysts and ligands, as well as an increased understanding of the mechanisms, has contributed substantially to recent advances in the field. Traditionally, organic reactions are carried out by conductive heating with an external heat source (for example, an oil bath). However, the application of microwave irradiation is a steadily gaining field as an alternative heating mode since its dawn at the end of the last century. This tutorial review focuses on some of the recent developments in the field of cross-coupling reactions assisted by microwave irradiation.
The efficient generation of biaryl compounds and heterocycles via the advent of the transition-metal-free coupling reaction constitutes an important development in the last few years. Although early methods for the construction of such molecules involved transition metals, recent advances in the field have witnessed a myriad of elegant reports without the use of metal sources. The serendipitous discovery and observation of synthetic chemists have realized that there lies a great potential in exploiting the inherent reactivity of molecules in absence of transition metal. The key to the success of such coupling reactions is the use of a strong base, oxidant and a catalytic amount of N-donor ligands which contribute significantly. This review aims to highlight the recent progress in the field of transition-metal-free direct C-C and C-heteroatom bond forming reactions via the use of a strong base and (or) an oxidant.
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