Ru-catalyzed addition

Trost, B.M. and Indolese, A. (1993) Ruthenium-catalyzed addition of alkenes to acetylenes. Journal of the American Chemical Society, 115, 4361-2 Trost, B.M., Indolese, A., Mueller, T. J. J. and Treptow, B. (1995) A Ru catalyzed addition of alkenes to alkynes. Journal of the American Chemical Society, 117, 615—623. 

A. B. (2002) A Synthesis of trisubstituted alkenes by a Ru-catalyzed addition. Chemistry - A European Journal, 8, 2341-2349. 

Typical Reaction Conditions for the Ru-Catalyzed Addition of Haloalkanes to oct-l-ene (Fig. 32) [46]... 

Table 1 Regioselectivity of the Ru-catalyzed addition of benzoic acids to tmninal alkynes...

The cascade process reported by Varela et al. [14] involved a Ru-catalyzed addition of alkenes 15 to 1,6-diynes 16 and a thermal 6ji electrocycUzation (Scheme 5.7). A reaction producing polycyclic cyclohexadienes 17 is performed under a catalytic mixture of 10% [Cp Ru(CH3CN)3]PF and 10% Et NCl at 80°C. 

Table II. Model reaction in Ru catalyzed addition of acetophenone...

A-A/B-B monomers, polycondensations, 157 A-B monomers, polycondensations, 157 AB monomers, self-polymerization via benzimidazole-activated ether synthesis, 266--274 Acetophenones Ru-catalyzed addition, 67-69 Ru-catalyzed step-growth copolymerization with a,(0-dienes for high-molecular-weight polymer synthesis, 99-112 4-(Acryloxy)benzoic acid, ordered polymer synthesis, 442-450 Acyclic diene metathesis polymerization cycle, 116,118/... 

Table 2.7 Ru-catalyzed addition of alkenes 2.174a-k to 1,6-diynes 2.173a-c followed by 6e electrocyclization.

Recently, Yu and co-workers developed an operationally simple catalytic system based on [RuCl2(/>-cymene)]2 for stereoselective cyclization of a-diazoacetamides by intramolecular carbenoid C-H insertion.192 /3-Lactams were produced in excellent yields and >99% m-stereoselectivity (Equation (53)). The Ru-catalyzed reactions can be performed without the need for slow addition of diazo compounds and inert atmosphere. With a-diazoanilide as a substrate, the carbenoid insertion was directed selectively to an aromatic C-H bond leading to y-lactam formation (Equation (54)). 

Related catalytic enantioselective processes It is worthy of note that the powerful Ti-catalyzed asymmetric epoxidation procedure of Sharpless [27] is often used in the preparation of optically pure acyclic allylic alcohols through the catalytic kinetic resolution of easily accessible racemic mixtures [28]. When the catalytic epoxidation is applied to cyclic allylic substrates, reaction rates are retarded and lower levels of enantioselectivity are observed. Ru-catalyzed asymmetric hydrogenation has been employed by Noyori to effect the resolution of five- and six-membered allylic carbinols [29] in this instance, as with the Ti-catalyzed procedure, the presence of an unprotected hydroxyl function is required. Perhaps the most efficient general procedure for the enantioselective synthesis of this class of cyclic allylic ethers is that recently developed by Trost and co-workers, involving Pd-catalyzed asymmetric additions of alkoxides to allylic esters [30]. 

The Ru-catalyzed cyclocarbonylation of a-allenic sulfonamides proceeds in the presence of Et3N under a CO atmosphere (20 atm) to yield ,/funsaturated lactams (Scheme 16.32) [36], In order to gain an insight into the reaction mechanism, a deuterium-substituted a-allenic sulfonamide was subjected to the carbonylation. The deuterium was found to be totally transferred to the methyl group. Based on this observation, a mechanism has been proposed which involves a ruthenacycle derived from addition of the Ru-H to the terminal double bond of allene (Scheme 16.33). 

In addition, the catalyst appeared very stable under the reaction conditions little carbon was deposited on the spent catalyst. Other supported metals were less active. The activity order, Ru Rh > Ni > Ir > Co > Pt > Pd > Fe, is very comparable to that measured for the steam reforming of methane. Of all the supports tested, Y203 and Zr02 gave the best results for the Ru-catalyzed steam reforming of glycerol. 

A significant improvement was achieved when Shvo s Ru-catalyst 2 (Fig. 12b) was employed in combination with the addition of DMP to suppress dehydrogenation reactions [106]. Poly-(R)-6-MeCL, with a promising ee of 86% and Mp of 8.2 kDa, was obtained after workup starting from optically pure (5 )-6-MeCL. The low rate of reaction compared to DKR (typically complete after 48 h with the Shvo catalyst) is attributed to the low concentration of the terminal alcohol as well as to the iterative nature of the system. Racemic 6-MeCL showed comparable rates of reaction for both enantiomers, which polymerized within 220 h with complete conversion of both enantiomers, yielding polymers of high ee (92%) and Mp (9.4 kDa). Successful polymerizations with more than 100 consecutive and iterative enzymatic additions and Ru-catalyzed racemizations on one polymer chain were realized. 

Their utility has been demonstrated in various Friedel-Crafts reactions,44-47 halogen addition,48 49 electrophilic nitration of aromatics,50 and various hydrogenation processes51-53 including the Ru-catalyzed hydrogenation of C02 to /V,/V-dipropyl formamide in supercritical C02 under biphasic conditions 54 The use of in situ IR spectroscopy allowed Horvath and coworkers to demonstrate that the same substrate-catalyst and product-catalyst complexes are produced in Friedel-Crafts acetylation of benzene in ionic liquids as in CH2C12 55... 

Some radical reactions occur under the control of transition metal templates. The first example of asymmetric creation of an asymmetric carbon with a halogen atom is shown by the a DIOP-Rh(I) complex-catalyzed addition of bromotrichloromethane to styrene, which occurs with 32% enantioselectivity (Scheme 99) (233). Ru(II) complexes with DIOP or BINAP ligands promote addition of arenesulfonyl chlorides to afford the products in 25-40% ee (234). A reaction mechanism involving radical redox transfer chain process has been proposed. 

Functionalized alkenes are used for the cooligomerization. Phenyl-1,4,8-decatriene (104) is obtained by the Ni-catalysed 1 2 addition of styrene and butadiene [42a], Pd catalyst affords the 1 1 adduct [43], Co or Fe catalyst gives the 1 1 adducts 105 and 106 of methyl acrylate and butadiene [44,42a], The 1 1 adducts 107 and 108 are obtained by the Ru-catalyzed coupling of butadiene and acrylamide [45]. Reaction of methyl methacrylate affords the 1 2 adduct 109 with Ni—PhjP catalyst at 0°C, whereas the oligomer 110 is obtained at higher temperature [46],... 

Several related examples of transition metal-catalyzed addition of C-H bonds in ketones to olefins have been reported (Table 2) [11-14]. The alkylation of diterpenoid 6 with olefins giving 7 proceeds with the aid of Ru(H)2(CO)(PPh3)3 (A) or Ru(CO)2(PPh3)3 (B) as catalyst [11], Ruthenium complex C, Ru(H)2(H2)(CO) (PCy3)2, has catalytic activity in the reaction of benzophenone with ethylene at room temperature [12]. The alkylation of phenyl 3-pyridyl ketone 8 proceeds with A as catalyst [13], Alkylation occurs selectively at the pyridine ring. Application of this C-H/olefin coupling to polymer chemistry using ce,co-dienes such as 1,1,3,3-tetramethyl-l,3-divinyldisiloxane 11 has been reported [14]. 

These catalytic reactions provide a unique pathway for addition of aromatic C-H bonds across C=C bonds. In contrast with Friedel-Crafts catalysts for olefin hydroarylation, the Ru-catalyzed hydrophenylation reactions of a-olefins selectively produce linear alkyl arenes rather than branched products. Although the selectivity is mild, the formation of anti-Markovnikov products is a unique feature of the Ru(II) and Ir(III) catalysts discussed herein. Typically, the preferred route for incorporation of long-chain linear alkyl groups into aromatic substrates is Friedel-Crafts acylation then Clemmensen reduction, and the catalysts described herein provide a more direct route to linear alkyl arenes. 

Chiral bis(oxazolines) 51 with an oxalylic acid backbone were used for the Ru-catalyzed enantioselective epoxidation of tran5-stilbene yielding franx-l,2-diphenyloxirane in up to 69% ee [24]. The asymmetric addition of diethylzinc to several aldehydes has been examined with ferrocene-based oxazoline ligand 52 [25], resulting in optical yields from 78-93% ec. The imide 53 derived from Kemp s triacid containing a chiral oxazoline moiety was used for the asymmetric protonation of prochiral enolates [26]. Starting from racemic cyclopentanone- and cyclohexanone derivatives, the enantioenriched isomers were obtained in 77-98 % ee. 

Fiirstner and co-workers have demonstrated the utility of the PtCl2-catalyzed carboalkoxylation of protected o-alkynyl phenols in the synthesis of the pterocarpene nucleus of erypoegin H <2007AGE4760>. Naphthalene fused 2,3-dihydrofurans have been shown to be available through a Pt- and Ru-catalyzed aromatization of enediynes with concomitant intramolecular nucleophilic additions <2007S2050>. 

As vinyl ethers were known to be poor substrates in Ru-catalyzed olefin metath-eses, it has been difficult to obtain cydic enol ethers by RCM of the vinyl ethers. Recently, a novel method to obtain cyclic enol ethers has been reported, which afforded cydic enol ethers directly from easily prepared dienes containing an allyl ether moiety [46]. Treatment of 70 with diene 99 in CH2CI2 in the presence of small amount of H2 resulted in a formation of dihydropyran 101 (Eq. 12.40). Treatment of 70 with H2 has been thought to produce an active catalyst for the olefin isomerization, and only metathesis products are formed until a small amount of H2 is introduced in the reaction. These results implied that this reaction most likely proceeded by way of a formation of the cyclic olefin 100, which was subsequently converted to dihydropyran 101 by the newly formed isomerization catalyst. In addition to the tandem reaction shown in Eq. 12.40, another method for obtaining cydic enol ethers from allyl ethers has also been demonstrated [46b]. This method induded addition of the hydride donor, such as NaBH4, to the reaction solution after the metathesis reaction had been completed. Although attempts to observe an active species for olefin isomerization in the presence H2 failed, these results suggested participation of hydride species in the olefin isomerization. 

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