Ruthenium-Catalyzed Transformations

Based on Watanabe s intermolecular hydroacylation of olefins with aldehydes,348 Kondo and Misudo developed the first ruthenium-catalyzed hydroacylation of 1,3-dienes with aldehydes (Scheme 71). Usually, palladium-mediated hydroacylations of 1,3-dienes with aldehydes give tetrahydropyran and/or open-chain homoallylic alcohol derivatives.350 However, in the present ruthenium-catalyzed transformations, the corresponding /3,7-unsaturated... 

In the course of a study on creation of a library of a great number of hetaryl ketones and related derivatives, Szewczyk et al. <2001AGE216> elaborated a ruthenium-catalyzed transformation of heterocycles with activated C-H bond by reaction with olefins and carbon monoxide. Thus, 253 gave 254, albeit in very poor yield. Synthetically, the more straightforward iron-catalyzed transformation was described by Fiirstner et al. <2002JA13856>. These authors reacted 255 with a Grignard reagent in the presence of Fe(acac)3 to afford the 7-alkyl-substituted derivative 256 in reasonable yield (acac = acetylacetonate). 

It is noteworthy that an illustrative review on tandem catalysis, including some ruthenium-catalyzed transformations, has recently appeared [3], which also proposed a useful definition rationalization effort. 

The double phosphinylation of propargylic alcohols with diphenylphos-phine oxide to form 2,3-bis(diphenylphosphinyl)-1-propenes is catalyzed by a thiolate-bridged diruthenium complex (Scheme 28) [69]. It has been shown that the reaction proceeds via three ruthenium-catalyzed transformations propargylation of the phosphine oxide, alkyne to allene isomerization, and addition of phosphine oxide to the allene structure. 

Palladium-catalyzed 1,4-diacetoxylation of diene 43 under chloride-free conditions stereoselectivity afforded diacetate 44, which was tranformed into monoacetate 45 [Eq.(39)l [69]. The latter compound was used in a ruthenium-catalyzed transformation. 

It is noteworthy that the regioselectivity of this ruthenium-catalyzed transformation proved complementary to the one observed when applying either palladium [89, 90] or copper [91] catalysts to the conversion of these substrates. 

Two interesting bifunctional polymeric ligands have been reported. Incorporating BINAP and BINOL functionalities, and 130 have been used in ruthenium-catalyzed transformations with considerable success. 

Starting from the same substrates, even hydroquinones can be prepared by insertion of two molecules of CO. In 1998, Mitsudo and coworkers [21a] demonstrated that hydroquinones could be achieved in a ruthenium-catalyzed cyclocarbonylation by using alkynes and 2-norbornenes. UnsymmetricaUy substituted hydroquinones were obtained in high yields by this novel ruthenium-catalyzed transformation. For the preparation of higher substituted hydroquinones, functionalized alkenes could... 

Based on this proposal, ruthenium-catalyzed direct arylations with aryl halides in less-coordinating apolar solvents (e.g. toluene) were probed. Interestingly, this catalytic system enabled regioselective C—H bond functionahzations at the aromatic moieties of N-aryl-substituted 1,2,3-triazoles (Scheme 9.33) [44]. It is noteworthy, that the regioselectivity of this ruthenium-catalyzed transformation proved complementary to that obtained when applying either palladium- or copper-based catalysts (vide infra). 

Naota T, Murahashi SI (1991) Ruthenium-catalyzed transformations of amino alcohols to lactams. Synlett 693... 

Related ruthenium-catalyzed transformations were also studied using 6-chloro-4-hydroxycoumarin as the starting material and microwave (MW) irradiation as the heating source [71]. Selective formation of a 2-methylene-2,3-di-hydrofuran unit, instead of the expected 2-methylfuran one, was observed in this case (compounds 24 in Scheme 10). Only after prolonged MW irradiation at 100 °C, aromatization to the corresponding furo[3,2-c]coumarins could be achieved, pointing out the marked influence that the electron-withdrawing chloride substituent exerts on the chemical behavior of the 4-hydroxycoumarin unit. 

Recently, this process was incorporated into different ruthenium-catalyzed transformations in the same reaction vessel, leading to the development of several ruthenium-promoted tandem processes. 

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