Ruthenium catalysis allylation

Under the conditions of ruthenium catalysis, alcohols and allylic acetates couple to form enones,... 

The formation of allenylidene derivatives from ethynyl-hexanol and alkenyl-vinylidene mononuclear complexes (9), the formation of mononuclear ruthenium allenyl complexes from terminal alkynes (10), the intermediacy of ruthenium-allenylidene complexes in forming propargylic alcohols (II), and in the cyclization of propargyl alcohols (12), and the use of mononuclear ruthenium compounds in allylic alkylation catalysis (13) have also been reported. 

Two mechanistic pathways, which differed in the way of ruthenium-mediated initial cleavage of formyl C-H or amido N-H bond, were proposed for the catalytic cycle. As shown in Scheme 7.3, an irreversibly cleavage of formyl C-H bond by the active ruthenium complex was followed by reversible insertion of the olefin into the Ru-H bond, which afforded either six-membered or seven-membered ruthenacycle. After reductive elimination, indolin-2-ones or 3,4-dihydroquinolin-2-one was formed. According to isotopic studies, pathway leading to six-membered lactams is postulated to be less favored. Another cyclization process initiated by Ru-catalyzed oxidative addition of formyl N-H bond (Scheme 7.4) was similar to Carreira s proposal for their hydrocarbamoyla-tion reaction of allylic formamides under similar ruthenium catalysis conditions [7]. The 6-endo cyclization process is proposed to be favored under the catalytic system B. 

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

High chemoselectivity is observed in this ruthenium-catalyzed isomerization of allylic alcohols. Simple primary and secondary alcohols and isolated double bonds are not affected by these catalysts. Furthermore, free hydroxy group is essential for this catalysis. The reaction of l-acetoxycyclododec-2-ene-4-ol furnished 4-acetoxycyclododecanone in high yield (Scheme 14).37... 

Dihydropyrroles have recently become readily available by ring-closing metathesis. For this purpose, N-acylated or N-sulfonylated bis(allyl)amines are treated with catalytic amounts of a ruthenium carbene complex, whereupon cyclization to the dihydropyrrole occurs (Entries 6 and 7, Table 15.3 [30,31]). Catalysis by carbene complexes is most efficient in aprotic, non-nucleophilic solvents, and can also be conducted on hydrophobic supports such as cross-linked polystyrene. Free amines or other soft nucleophiles might, however, compete with the alkene for electrophilic attack by the catalyst, and should therefore be avoided. 

Hydroformylation - [CARBON MONOXIDE] (Vol 5) - [OXO PROCESS] (Vol 17) -of allyl alcohol [ALLYL ALCOHOL AND MONOALLYL DERIVATIVES] (Vol 2) -catalysts for [CATALYSIS] (Vol 5) -C-19 dicarboxylic acids from [DICARBOXYLIC ACIDS] (Vol 8) -of ethylene [ETHYLENE] (Vol 9) -of ethylene [PROPYL ALCOHOLS - N-PROPYLALCOLHOL] (Vol 20) -of maleate and fumarate esters [MALEIC ANHYDRIDE, MALEIC ACID AND FUMARIC ACID] (Vol 15) -phosphine catalyst [PHOSPHORUS COMPOUNDS] (Vol 18) -platinum-group metal catalysts for [PLATINUM-GROUP METALS] (Vol 19) -rhodium catalysis [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -ruthenium cmpds or catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -use of coordination compounds [COORDINATION COMPOUNDS] (Vol 7)... 

Although mechanistically different, a successful kinetic resolution of cyclic allyl ethers has recently been achieved by zirconium catalysis [2201. Other metals such as cobalt [221], ruthenium [222], and iron [2231 have been shown to catalyze allylic alkylation reactions via metal-allyl complexes. However, their catalytic systems have not been thoroughly investigated, and the corresponding asymmetric catalytic processes have not been forthcoming. Nevertheless, increasing interest in the use of alternative metals for asymmetric alkylation will undoubtedly promote further research in this area. 

The same concept is applicable to allylic alcohols, ketones, or ketoximes. Enol acetates or ketones were successfully converted in multi-step reactions to chiral acetates in high yields and optical yields through catalysis by Candida antarctica lipase B (CALB, Novozyme 435) and a ruthenium complex. 2,6-Dimethylheptan-4-ol served as a hydrogen donor and 4-chlorophenyl acetate as an acyl donor for the conversion of the ketones (Jung, 2000a). 

Asymmetric catalysis undertook a quantum leap with the discovery of ruthenium and rhodium catalysts based on the atropisomeric bisphosphine, BINAP (3a). These catalysts have displayed remarkable versatility and enantioselectivity in the asymmetric reduction and isomerization of a,P- and y-keto esters functionalized ketones allylic alcohols and amines oc,P-unsaturated carboxylic acids and enamides. Asymmetric transformation with these catalysts has been extensively studied and reviewed.81315 3536 The key feature of BINAP is the rigidity of the ligand during coordination on a transition metal center, which is critical during enantiofacial selection of the substrate by the catalyst. Several industrial processes currently use these technologies, whereas a number of other opportunities show potential for scale up. 

Ruthenium-catalyzed allylic alkylation falls between known catalysis with respect to regioselectivity and chirality of products. Like Pd, Mo, and W-but unlike Rh regioselectivity is not highly dependent on the nature of the starting carbonate. However, unlike Pd and Mo, but similar to Rh and W, substitution of the chiral substrate occurs with high retention of configuration, (equation 75). Hence the Ru system compliments other metal-catalyzed allylic systems well. ... 

The resolution of racemic secondary allyl alcohols can be performed in the presence of certain ruthenium chiral catalysts through enantioselective asymmetric hydrogenation [811, 881], Chiral poisoning also works in such kinetic resolutions. For example, hydrogenation of 2-cyclohexenol under ( )-binap-Ru catalysis in the presence of (II , 25)-ephedrine 1.61 (10 equiv) provides unreacted (J )-2-cydo-hexenol in 95% ee after 60% conversion [857],... 

Ruthenium complexes attract recent interest as new promising candidates for efficient, specific and environmentally benign allylation catalysts. It is noticeable that some J7 -allylruthenium(II) complexes have an ambiphilic property in catalysis involving the C-0 bond activation [52]. When allyl carboxylates or carbonates are treated with nucleophilic 1,3-dicarboxylates or electrophilic aldehyde in the presence of Ru complexes, catalytic allylations of nucleophiles or electrophiles take place [53]. In both reactions, J7 -allylruthenium complexes are assumed to be intermediates. Independent synthesis and reactions of the model compounds support this observation (Scheme 3.28). This ambiphilicity of the allylruthenium(II) may arise from the different reactivity of and rf forms in the allylic moiety [54]. 

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