Ring ruthenium-catalyzed

The ruthenium-catalyzed isomerization of aryl allyl ethers or amines followed by ring-closing metathesis with ruthenium catalyst 1 furnishes fused benzo-heterocycles in good yield (Scheme 40).66 67... 

The alkylation of olefinic G-H bonds proceeds when conjugated enones are employed in the ruthenium-catalyzed reaction with alkenes, as shown in Equation (16).1 7 Among the acylcyclohexenes, 1-pivaloyl-l-cyclohexene exhibits a high reactivity and the presence of an oxygen atom at the allylic position in the six-membered ring increases the reactivity of the enones. Some terminal olefins, for example, triethoxyvinylsilane, allyltrimethylsilane, methyl methacrylate, and vinylcyclohexane, are applicable for the alkylation of the olefinic C-H bonds. Acyclic enones also undergo this alkylation. 

The proposed catalytic cycle of the ruthenium-catalyzed intermolecular Alder-ene reaction is shown in Scheme 21 (cycle A) and proceeds via ruthenacyclopentane 100. Support for this mechanism is derived from the observation that the intermediate can be trapped intramolecularly by an alcohol or amine nucleophile to form the corresponding five-or six-membered heterocycle (Scheme 21, cycle B and Equation (66)).74,75 Four- and seven-membered rings cannot be formed via this methodology, presumably because the competing /3-hydride elimination is faster than interception of the transition state for these substrates, 101 and 102, only the formal Alder-ene product is observed (Equations (67) and (68)). 

The enantioseiective hydrogenation of a-amino ketones has been applied extensively to the synthesis of chiral drugs such as the / -agonist SR 58611 (Sanofi Cie). m-Chlorstyreneoxide was obtained via carbene-induced ring closure of the amino alcohol. Epoxide-opening by a chiral amine obtained via a ruthenium-catalyzed hydrogenation of an enamide has led to the desired compound where... 

For a review of asymmetric Mo-catalyzed metathesis, see Catalytic Asymmetric Olefin Metathesis, A. H. Hoveyda, R. R. ScHROCK, Chem. Eur. J. 2001, 7, 945-950 for reports on chiral Ru-based complexes, see (b) Enantioselective Ruthenium-Catalyzed Ring-Qosing Metathesis, T.J. Sei-DERS, D.W. Ward, R.H. Grubbs, Org. Lett. 2001, 3, 3225-3228 (c) A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis In Air, J. J. Van Veldhuizen, S. B. 

Pahnans et al. prepared 5 by the reaction of [RuCl2(p-cymene)]2 and 2-phenyl-2-aminopropionamide in the presence of potassium carbonate. They used 5 in an iterative tandem catalysis for the synthesis of chiral oligoesters. The enzymatic ring opening of 6-methyl-e-caprolactone was combined with ruthenium-catalyzed alcohol racemization to produce optically active oligomers of 6-methyl-e-capro-lactone [23] (Scheme 1.17). 

An interesting case of ruthenium-catalyzed isomerization versus ring opening of differently substituted 2-vinyl-l,3-dioxanes has been reported. It was found that 5,5-dialkyl-substituted dioxanes gave the ring-opened enol ethers and 5,5-unsubstituted dioxanes afforded the (expected) 2-alkylidene-l,3-dioxanes (Scheme 89) <1996PJC1087>. 

A solid-phase synthesis of furo[3,2-3]pyran derivatives utilizing highly functionalized sugar templates has been reported <2003JOC9406>. After incorporation of alkenes within the sugar template, such as compound 95, the solid support is introduced via formation of the acid amide. This immobilized system then allows a ruthenium-catalyzed ring-closing metathesis that leads to the formation of the fused oxacycles. 

In 2001, Takahashi and his co-workers developed the first asymmetric ruthenium-catalyzed allylic alkylation of allylic carbonates with sodium malonates which gave the corresponding alkylated compounds with an excellent enantioselectivity (Equation (Sy)). Use of planar-chiral cyclopentadienylruthenium complexes 143 with an anchor phosphine moiety is essential to promote this asymmetric allylic alkylation efficiently. The substituents at the 4-position of the cyclopentadienyl ring play a crucial role in controlling the stereochemistry. A kinetic resolution of racemic allylic carbonates has been achieved in the same reaction system (up to 99% ee). ... 

The cyclization of A-alkenyl derivatives of resin-bound peptides by ruthenium-catalyzed ring-closing metathesis has been investigated [426-428]. These reactions do not proceed well on insoluble supports, and cyclizations in solution are generally more successful. 

A dominant feature of the type c ring-construction approach to azepine systems has been ruthenium-catalyzed ringclosing metathesis reactions. Examples include the synthesis of the azepine derivative 157 from 156 using either the Grubbs type I catalyst 159 or type II 160. The diene precursor 156 was prepared in turn from 154 via 155, as shown in Scheme 21. Hydrogenation of the C-C double bond in 157 afforded the azepane 158 <2005SL631>. 

It is noted that, while numerous type c (Section 13.01.6.3) and type d (Section 13.01.6.4) ring-constmction manifestations of the ruthenium-catalyzed ring-closing metathesis reaction for the azepine ring formation have been reported, the corresponding type b possibility, with an iV-vinyl component, has not as yet been reported. 

Platinum or ruthenium catalyzes the ring closure of a silanylethene giving the 1,3-disiletane via intramolecular hydrosilylation (Scheme 26) <2001JOM127>. 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

Dimcthyl 2-(but-2-ynyl)-2-(5-oxopent-3-enyl)malonates 96 undergo ruthenium-catalyzed intramolecular cycli-zations to yield cyclohexyl fused 4//-pyrans 97, most likely via formation of and reductive elimination from the ruthenacycle intermediate 98 (Scheme 32). Likewise, internal alkynes tethered to an a, 3-unsaturated ketone via a three-component chain undergo mthenium-catalyzed cyclizations furnishing 4//-pyrans that are fused to five-membered rings 99 (Equation 50) <2000JA5877>. 

A palladium(ll)-catalyzed reaction between 1-heptyne and hydroxyalkynoates 215 provides a route to 3,4-dihydropyrans that feature an ( )-exocyclic double bond (Equation 99) <2000JA11727>. A ruthenium-catalyzed double-ring closure of the diynols 216 furnishes fused 3,4-dihydropyrans in excellent yield (Equation 100) <2004OL4235>. 

A ruthenium-catalyzed ring opening cross-metathesis of 8-oxabicyclo[3.2.1]oct-6-en-3-one 1049 with alkenes provides an efficient method for the preparation of substituted tetrahydropyran-4-ones 1050 (Equation 408, Table 50) <1999X8169, 20010L4275>. Similarly, ozone can be used to cleave the same ring system during the synthesis of chiral tetrahydropyran-4-ones <2006T257>. 

Fig. 47 Ruthenium-catalyzed ring opening reactions of endoperoxides...

---