Direct ruthenium-catalyzed

Directed ruthenium-catalyzed hydroesterifications of alkenes, employing 2-pyridylmethyl formate, leads to esters (Equation (136)). With vinyl ethers a-adducts are obtained (Equation (137)). 

Magee and Norton reported the direct, ruthenium catalyzed asymmetric hydrogena... 

Hydroxyl-Directed Ruthenium-Catalyzed C-H Bond Functionalization Versatile Access to Fluorescent Pyrans... 

Bergman SD, Storr TE, Prokopcova H, Aelvoet K, Diels G, Meerpoel L, Maes BUW (2012) The role of the alcohol and carboxylic acid in directed ruthenium-catalyzed C(sp )-H a-aUcylation of cyclic amines. Chem Eur I 18 10393—10398... 

Promising applications for metal-NHC compounds in materials science and medicinal chemistry are based on the strong metal-carbon bond and the high donor capability of the NHC. The most extensive investigations have been carried out in the field of homogeneous catalysis. Here, NHCs have to be considered as typical directing or innocent spectator ligands, best comparable to trialkylphosphines. The recent successful applications of NHCs in ruthenium-catalyzed olefin metathesis... 

The ruthenium-catalyzed direct addition of saturated aliphatic alcohols to non-activated alkynes remains a challenge. Only ally alcohol has been successfully involved in the intermolecular addition to phenylacetylene to produce an ether and the enal resulting from Claisen rearrangement (Equation 10.7) [24]. Thus, in refluxing toluene, in the presence of a catalytic amount of RuCl(tris(pyrazolyl) borate) (pyridine)2, a 1 1 mixture of ally P-styryl ether and 2-phenylpent-4-enal was obtained in 72% overall yield. 

Isomerization of allylic alcohol to ketone has been extensively studied [13], and two different pathways have been established, including tt-allyl metal hydride and the metal hydride addition-elimination mechanisms [5,14]. McGrath and Grubbs [ 15] investigated the ruthenium-catalyzed isomerization of allyl alcohol in water and proposed a modified metal hydride addition-elimination mechanism through an oxygen-functionality-directed Markovnikov addition to the double bond. 

Recently, a new type of reaction - that is, aerobic oxidative cyanation of tertiary amines - was discovered. In this reaction, oxidation with molecular oxygen in place of peroxides, in addition to direct carbon-carbon bond formation by trapping of the iminium ion intermediates with a carbon nucleophile under oxidative conditions, is accomplished simultaneously. The ruthenium-catalyzed oxidation of tertiary amines with molecular oxygen (1 atom) in the presence of sodium cyanide gives the corresponding a-aminonitriles (Eq. 3.74) [132], which are useful for synthesis of a-amino acids and 1,2-diamines. 

Bicyclic mthenacydopentenes are considered to be intermediates for these ruthenium-catalyzed PK reactions. The catalytic intermolecular PK reaction was recently realized by a combination of the ruthenium catalysis with alkenes possessing dimethylpyridylsilyl group (Scheme 4.37) [82]. With the directive aid of the pyridylsilyl group, putative mthenacyclopentene key intermediates such as 95 were expected to be formed selectively and, as a result, the PK reaction took place even under 1 atm CO to afford regioselectively the desired cyclopentenone after facile concomitant desilylation via 96. 

Here, we shall focus on ruthenium-catalyzed nucleophilic additions to alkynes. These additions have the potential to give a direct access to unsaturated functional molecules - the key intermediates for fine chemicals and also the monomers for polymer synthesis and molecular multifunctional materials. Ruthenium-catalyzed nucleophilic additions to alkynes are possible via three different basic activation pathways (Scheme 8.1). For some time, Lewis acid activation type (i), leading to Mar-kovnikov addition, was the main possible addition until the first anfi-Markovnikov catalytic addition was pointed out for the first time in 1986 [6, 7]. This regioselectiv-ity was then explained by the formation of a ruthenium vinylidene species with an electron-deficient Ru=C carbon site (ii). Although currently this methodology is the most often employed, nucleophilic additions involving ruthenium allenylidene species also take place (iii). These complexes allow multiple synthetic possibilities as their cumulenic backbone offers two electrophilic sites (hi). 

For the chelation-assisted catalytic reaction, Jt-electrons in a nitrile group are able to function as a directing group. The ruthenium-catalyzed alkylation of aromatic nitriles with triethoxyvinylsilane takes place predominantly at the ortho position (Eq. 9.10) [24]. This regioselectivity indicates the possibility of Jt-coordination of the CN group to the ruthenium in the catalytic cycle. 

On the other hand, Murai and coworkers succeeded in the ruthenium-catalyzed activation of the C-H bonds of aromatic, heteroaromatic and olefmic compounds that had directing groups [74] (see Chapter 9), by applying Moore s concept to their catalytic systems (Eq. 11.31). 

Cyclic sulfates provide a useful alternative to epoxides. These cyclic compounds are prepared by reaction of the diol with thionyl chloride, followed by ruthenium-catalyzed oxidation of the sulfur (Scheme 3.30) [341-343]. The cyclic sulfates can also be accessed by direct reaction of the diol with sulfuryl chloride (Scheme 3.30) [344]. 

Ruthenium-Catalyzed Direct Arylations Through C-H Bond Cleavages... 

Abstract Stoichiometric cycloruthenation reactions of substrates containing Lewis-basic functionalities set the stage for efficient ruthenium-catalyzed C-H bond functionalization reactions. Thereby, selective addition reactions of C-H bonds across alkenes or alkynes enabled atom-economical synthesis of substituted arenes. More recently, ruthenium-catalyzed direct arylation reactions were examined, which display an unparalleled scope and, hence, represent economically and environmentally benign alternatives to traditional cross-coupling chemistry. 

Stoichiometric cycloruthenation reactions, as well as the early example of catalytic deuteration of phenol (see above) [38] served for the development of efficient catalytic strategies for C-C bond formations through C-H bond functionalizations. Indeed, ruthenium-catalyzed atom-economical [51] addition reactions of arenes onto C-C multiple bonds, hydroarylations [52-57], were found to be very useful. In an early example, Lewis and Smith disclosed a regioselective alkylation of phenol through in situ formation of its phosphite, and subsequent directed C-H bond functionalization (Scheme 8) [58],... 

While this protocol relied on the in situ generation of the relevant phosphite for catalytic hydroarylation reactions, Murai and coworkers developed effective methodologies for the direct use of Lewis-basic substrates, such as acetophenone 20 (Scheme 9) [18, 59], Thereby, regioselective ruthenium-catalyzed anti-Markovnivkov alkylations and alkenylations were accomplished using alkenes or alkynes [60] as substrates, respectively. Recently, an extension of this protocol to terminal alkynes was reported, which involved a phosphine ligand-free catalytic system (see below), along with stoichiometric amounts of a peroxide [61]. 

Scheme 17 Ruthenium-catalyzed direct arylation of aldimine 42...

Scheme 18 Ruthenium-catalyzed direct arylation with phenyl bromide (47)...

---