Cyclization—Homogeneous

Abstract

Development of highly efficient catalytic processes for the synthesis of natural and unnatural compounds of medicinal interest or useful as intermediates for functional materials is a central focus in modern organic synthesis. One of the most efficient approaches to such methodology developments is to apply transition‐metal catalyzed cyclization reactions for the transformations of simple starting materials into monocyclic, bicyclic, and polycyclic scaffolds that can be further elaborated into specific targets. This article concisely summarizes recent advances in the cyclizations promoted by homogeneous catalysts, including various carbocyclizations, carbonylative carbocyclizations, cyclohydrocarbonylations, intramolecular hydrosilylations, and silylformations, compiling relevant references up to late 2008. Among these catalytic cyclization processes, the carbocyclization and carbonylative carbocyclization are extremely important and useful reactions for the syntheses of a variety of carbocyclic and heterocyclic compounds. Cascade carbocyclization is a powerful method, providing a rapid access to polycyclic skeletons in one step. Cyclohydrocarbonylation is another powerful catalytic cyclization process, which finds a host of applications in organic syntheses. Intramolecular hydrosilylations and silylformations also provide unique methods for a variety of organic syntheses. Accordingly, catalytic cyclization reactions not only serve as highly useful synthetic methods in laboratories but also have high potential as future industrial processes.

An Efficient Synthesis of Novel Fused Cycloheptatrienes through Mn(II)-Mediated Formal Intermolecular [2 + 2 + 2 + 1] Cycloaddition

“…Much effort has therefore been devoted to this activity, and considerable advances have been made in the development of cycloaddition reactions. , Cycloaddition is widely regarded as one of the most efficient means for the construction of cyclic compounds on account of its ability to form at least two bonds in one operation . The transition-metal-catalyzed cycloaddition reactions are the most useful processes for the rapid construction of a complex ring system. , Various transition metals have been commonly used to promote these processes, such as nickel, ruthenium, cobalt, rhodium, palladium, and so on. , …”

“…Among the various types of cycloadditions, the [2 + 2 + 2 + 1] cycloaddition is rarely reported for the synthesis of cycloheptatriene derivatives, since it is a higher self-sequential process than others. − In 2003, Barluenga’s group reported a novel nickel-mediated [2 + 2 + 2 + 1] cyclization for the construction of the cycloheptatriene chromium complexes by the reaction of Fischer carbene complexes and alkynes (Scheme a) . Ojima and co-workers subsequently reported a novel Rh-catalyzed intramolecular [2 + 2 + 2 + 1] cycloaddition reaction for the synthesis of fused tropones from triyne substrates and CO (Scheme b) . Herein, a Mn(II)-mediated formal intermolecular [2 + 2 + 2 + 1] cycloaddition reaction is described for the efficient construction of novel fused cycloheptatriene derivatives from easily available N -(acyl­methyl)­pyridinium iodides and naphtho­quinone (Scheme c).…”