Carbon—heteroatom bond formation heterocycles

This review outlines the recent advances in the synthesis of heterocyclic compounds utilizing ruthenium catalysts. The first part is devoted to the synthesis of heterocycles via carbon-heteroatom bond formations. Heterocyclic frameworks are also constructed by ring closure of heteroatom-tethered acyclic molecules. The second part covers the ruthenium-catalyzed carbon-carbon bond forming cyclizations yielding heterocycles. Other examples, in which ruthenium catalysis indirectly participates in heterocycle formation, are collected in the final section. Although a heterocyclic ring was formed without catalysis, ruthenium-catalyzed processes play pivotal roles in such examples. 

Transition-Metal-Based Carbon-Carbon and Carbon-Heteroatom Bond Formation for the Synthesis and Decoration of Heterocycles... 

Maes BUW (2006) Transition-Metal-Based Carbon-Carbon and Carbon-Heteroatom Bond Formation for the Synthesis and Decoration of Heterocycles. 1 155-211 Maiti M, Kumar GS (2007) Protoberberine Alkaloids Physicochemical and Nucleic Acid Binding Properties. lO. 155-210... 

The transition metal catalyzed synthesis of seven membered and larger heterocycles attracted considerably less attention than the preparation of their five and six membered analogues. Typical examples in this chapter include the formation of heterocycles in insertion reactions, or through carbon-heteroatom bond formation. Although the formation of some macrocyclic natural products was also achieved in cross-coupling reactions they will not be discussed in detail. 

One of the major uses of double-bonded functional groups in organic synthesis is the preparation of heterocyclic compounds. These compounds are either target molecules of a particular synthetic sequence, or are key intermediates in organic synthesis. This section covers the synthesis of heterocyclic compounds by carbon-heteroatom bond formation or by C—C bond formation. Epoxidation of alkenes is not covered here, but in Section II.A. Subdivision, for ease of reading, is by ring size, for the most part. 

The synthesis of a great wealth of other heterocyclic compounds from halides, by carbon-heteroatom bond formation in the key step, is also an important area of organic synthesis and especially of natural product work. Recent reviews have considered key synthetic intermediates of this type946,947. Hence this section only briefly reviews the formation of some N-, O- and S-containing heterocyclic compounds that have been the targets of recent synthetic pathways. 

Keywords Ruthenium catalysis Heterocyclic compounds Cyclization Carbon-heteroatom bond formation Carbon-carbon bond formation... 

Ruthenium catalysis has been extensively explored during the past decade [114]. Newly developed carbon-carbon bond forming cyclizations such as [2+2+2] cycloaddition, RCMs, and cycloisomerizations have dramatically expanded the scope of heterocycle synthesis. Relatively unexplored catalytic carbon-heteroatom bond formations have also made significant contributions to this area. Further progress in ruthenium catalysis will not only improve the conventional synthetic methodologies, but will also open the way to an unprecedented class of heterocyclic compounds, which might have a significant potential as pharmaceuticals or functional materials. 

Recently, radical species have attracted much attention as useful intermediates for carbon-carbon bond formations. By contrast, in organic synthesis, radicals centered on heteroatoms have not been widely utilized for construction of molecular skeletons with carbon-heteroatom bond formation. In this section we will discuss the generation of alkylideneaminyl radicals, conventionally called iminyl radicals from oxime derivatives by electron transfer reactions. AU -lideneaminyl radicals thus created are utilized for making nitrogen-containing heterocycles. 

Scheme 192. Reaction of Alkenyl Epoxides and Aziridines Producing Heterocycles via Carbon-Heteroatom Bond Formation by (a) Intramolecular Allylation of Oxygen and Nitrogen Nucleophiles and (b) Intermolecular [3 + 2]-Cycloaddition with Heterocumulenes...

This article discusses the anodic synthesis of heterocyclic compounds that have appeared during the last decade. The mechanistic aspects involving intramolecular, intermolecular cyclizations and the homogeneous vs heterogeneous anodic oxidations were considered. This review deals with the recent advances in anodic oxidations in which heterocyclic compounds were synthesized through carbon-heteroatom and heteroatom-heteroatom bond formation. 

Since in the synthesis of heterocyclic compounds the ring closure usually involves the formation of the carbon-heteroatom bond, in the retrosynthetic analysis the first bond to be disconnected is the carbon-heteroatom bond (Cf. heuristic principle HP-8), either directly or after the pertinent (FGI or FGA) functional group manipulation. For instance, compound 17 -which is the starting material for Stork s synthesis of Aspidosperma alkaloids [30]- may be disconnected as shown in Scheme 6.11. 

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