Transition-Metal-Catalyzed MBFTs

Treatment of the precursor 150 with Grabbs II catalyst (give structure of the catalyst in the scheme) initiated the key tandem ring-opening metathesis (ROM)/ring-closing metathesis (RCM) sequence, which led to the carbocyclic 

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The goal of this chapter is to highlight and discuss a selection of MBTFs employed in the total synthesis of natural products during the past 10 years. As MBTFs usually involve many distinct steps, which make it hard to classify them, this chapter is divided into five parts anionic-initiated MBFTs, cationic-initiated MBFTs, radical-mediated MBFTs, pericyclic MBFTs, and transition-metal-catalyzed MBFTs, hoping that the division can help show the MBFTs employed in the synthesis of natural products clearly and concisely. 

The 1,3-dipolar cycloaddition (1,3-DC) is the reaction of a dipolarophile with a 1,3-dipolar compound to form a five-membered ring, which is a kind of MBFT. The earliest 1,3-DC reactions were described in the late nineteenth century to the early twentieth century, following the discovery of 1,3-dipoles. Mechanistic investigations and synthetic applications were established by Rolf Huisgen in the 1960s [2], Now, the chemistry of the 1,3-DC reaction has thus evolved for more than 100 years, and a variety of different 1,3-dipoles have been discovered, which has significantly advanced the development of the 1,3-DC reactions. After several decades of development, transition-metal-catalyzed, stereoselective 1,3-DC has become one of the most useful synthetic routes to the synthesis of the five-membered heterocycles. 

This chapter summarized the application of MBFTs, including electrophilic, nucleophilic, transition-metal-catalyzed, pericyclic, and radical pathways, in the... 

In this last section, the focus shifts to intermolecular palladium-catalyzed MBFTs that are exploited for the synthesis of biologically active molecules. There are several reasons why palladium is one of the most widely employed transition metals. First, it allows facile oxidative insertion and reductive elimination. Second, palladium accepts a broad range of functional groups and its reactivity is heavily influenced by the addition of ligands. Last, by creating asymmetric catalytic complexes, stereoselective reactions are facilitated. Nevertheless, the metal is not commonly used in MBFTs for the synthesis of products that are tested for biologically activity. Therefore, only a few examples will be discussed which provide products that are currently exploited for their biological effect. 

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