Ruthenium catalysis cyclization, intramolecular

A nice addition to this work was made by Ellman and coworkers [100], who reported an intramolecular cyclization of aromatic ketones using Cp Rh (C2H3SiMe3)2 as catalyst (Scheme 19.69). This rhodium-catalyzed reaction was more efficient with respect to ruthenium catalysis (about 20% yield with RUH2 (CO)(PPh3)3), but its scope was limited to substrates bearing noniso-merizable olefins. 

A rhodium catalyst was also proposed for the intramolecular cyclization of imidazoles and oxazoles, which was previously shown to proceed under ruthenium catalysis (Scheme 19.61) [90bj. An enantioselective version was later reported... 

Under ruthenium catalysis, oxidative coupling of a,a-disubstituted benzy-lamines with acrylates can be performed efficiently at room temperature to produce (isoindol-l-yl)acetic acid derivatives (Eq. (7.48)) [58]. The reaction takes place accompanied by free amino group-directed orffio-alkenylation and successive intramolecular cyclization. 

Ruthenium-catalyzed heterocycle synthesis through C-H bond activation and cyclization has received an increasing interest in the past few years. In this chapter the oxidative cyclization reactions with a series of unsaturated small molecules under ruthenium catalysis have been summarized. Among these reactions, the formations of heterocycles were realized by several synthetic pathways after initial C-H bond activation, which involved formation of intramolecular C-C bond, intramolecular C-N bond, intermolecular C-C/C-O bonds, and intermolecular C-C/C-N bonds. On the other hand, many challenges still need to overcome, such as heterocycle synthesis via ruthenium-catalyzed C(sp )-H activation. On the basis of the solid and exciting progress, no doubt that more reactive... 

Murai et al. [14] found that Ru3(CO)12 shows a high catalytic activity for the intramolecular hetero-P-K-type reaction of yne-aldehydes (Eq. 4). A variety of substituents on the acetylenic moiety can be tolerated, and the application to cyclohexane-fused bicyclic systems is also feasible. Although the mechanism of this catalysis remains elusive, two pathways have been proposed as the initial step for the reaction in Eq. (4) via the oxidative cyclization of yne-aldehydes to a ruthenium center, leading to a metallacycle 3, or via the oxidative addition of an aldehyde C-H bond to ruthenium, leading to 4. 

Intramolecular addition of amine N-H bonds to carbon-carbon multiple bonds would afford nitrogen heterocycles. To realize catalytic cyclization of a,co-aminoalkenes or aminoalkynes, various catalytic systems have been developed especially with early transition metals such as titanium, zirconium, lanthanide metals, and actinide metals [ 12], Late-transition-metal catalysis based on Ni, Pd, and Rh has also proved to be efficient [ 12], Recently, the ruthenium-catalyzed intramolecular hydroamination of aminoalkynes 15 was reported to afford 5-7-membered ring products 16 in various yields (Eq. 6) [13]. Among... 

With the aid of transition-metal catalysis, heterocycle formations can be achieved not only by carbon-heteroatom bond forming cyclizations of an acyclic molecule with a terminal group such as alcohols and amines, but also by intramolecular carbon-carbon bond forming reactions of an acyclic precursor containing one or more heteroatoms in its tether moiety. This section will briefly survey heterocycle synthesis via carbon-carbon bond formations. For details of ruthenium-catalyzed C-C bond formations, see other chapters of this book. 

Ru Many examples of radical arylations by photoredox catalysis have been recently reported [62-64]. For instance, when ArN +X salts are reduced, a C—N bond cleavage occurs to give Nj, an Ar radical, and the anion X . An intramolecular photo-Pschorr reaction is exemplified by the conversion of ArN +X (89) into phenanthrene derivatives 92, in quantitative yields, photocatalyzed by [Ru(bpy)3](BF )j (Scheme 9.12). In this way, the excited state of this ruthenium complex was able to reduce the salt 89 to the corresponding aryl radical 90. This in turn cyclized, thereby... 

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