Double metal catalysis

Hydrometallation-cross-coupling and carbometallation-cross-coupling tandem protocols and other alkenyl-aryl, alkenyl-alkenyl, and alkenyl-alkynyl coupling reactions double metal catalysis... 

Scheme 35 Double metal catalysis in the production of the Sartan intermediate OTBN...

Synthesis of Carotenoids and Retinoids. The Pd-catalyzed cross-coupling reactions of 1 with alkenylmetals containing Al, Zn, and Zr have been shown to be high-yielding and selective. The reaction of 1 with /3,/3-disubstituted alkenylalanes under the conditions of double metal catalysis with Pd and Zn is satisfactory, and the >99% stereospecificity level can be maintained in most cases. Thus, this reaction used in conjunction with the Zr-catalyzed carboalumination of terminal alkynes forms the foundation of a highly stereoselective and... 

To find out applications and rules of the metala-logy principle, we systematically investigated the influence of HOMO/LUMO- or LUMO/HOMO-perturbations (dual model) as well as relative donor/acceptor- or acceptor/donor-interactions (double-dual model) in metal-complexesin their model-reactions and in metal catalysis The strategy we followed is depicted in Scheme 2.2-2. For our purposes, we separated the studied catalytic system into two r-systems (substrates S Case I),... 

The peculiar metal ion specificity of the ATP cleavage reaction may perhaps be explained by reference to some studies on the metal complexes of Schiff bases, which have provided clues to many aspects of biological metal catalysis. It was shown that metal ions will split the carbon-nitrogen double bond in thiophenalde-hyde-ethylenediamine (18, 21) as a consequence of the electronic-drift-to-metal... 

There are several possibilities for asymmetric synthesis in catalysed cyclopropanation and very substantial progress has already been made especially with catalyst development. The option of covalently attaching chiral auxiliaries to diazo compounds or to substrates, e.g. alkenes for cyclopropanation, has been discussed above in the subsection on diastere-oselectivity. The fact that many of the processes require metal catalysis makes the alternative option of using chiral catalysts particularly attractive and potentially more rewarding for commercial exploitation. The double option of combining the use of a chiral catalyst with a diazo compound carrying a chiral auxiliary is also available. For convenience, the double option is also included in this subsection. 

Aziridines can add to carbon—carbon multiple bonds. Elevated temperature and alkali metal catalysis are required in the case of nonpolarized double bonds (193—195). On the other hand, the addition of aziridines onto the conjugated polarized double or triple bonds of a,p-unsaturated nitriles (196—199), ketones (197,200), esters (201—205), amides (197), sulfones (206—209), or quinones (210—212) in a Michael addition-type reaction frequendy proceeds even at room temperature without a catalyst. The adducts obtained from the reaction of aziridines with a,p-unsaturated ketones, eg, 4-aziridinyl-2-butanone [503-12-8] from 3-buten-2-one, can be converted to 1,3-substituted pyrrolidines by subsequent ring opening with acyl chlorides and alkaline cyclization (213). 

Exposed multiple bonds of angular arenes are specifically prone to oxidation. The synthetic value of such double bonds arises from their high reactivity towards simple electrophiles, enophiles, and radicals. Heavy metal catalysis, periodate oxidation, and ozonolysis are the standard tools for oxidative bond cleavage in these substrates. For economic and ecological reasons, technically applicable alternatives are of great interest. Phenanthrene (29) represents a typical substrate... 

A widely applied strategy for the synthesis of various difunctionalized organic molecules, e.g. diols, dialdehydes, etc., relies on the oxidative cleavage of olelinic double bonds. Besides transition metal catalysis for asymmetric synthesis, periodate oxidation and ozonolysis are the standard tools for oxidative bond cleaving reactions. For economic and safety reasons, technically applicable alternatives to osmium-based chemistry and ozonolysis are of great interest. 

The crossover product, propionaldehyde-l,3-d-3- C 12, clearly demonstrated that the isomerization occurred via intermolecular 1,3-hydrogen shift. These results are consistent with a modified metal hydride addition-elimination mechanism which involves exclusive 1,3-hydrogen shift through oxygen-directed Markovnikov addition of the metal hydride to the carbon-carbon double bond (Scheme 12.2). The directing effect of functional groups on the selectivity of transition metal catalysis is well presented [9], and an analogous process appears to be operative in the isomerization of allylamines to enamines [10]. 

Direct initiation through higher valence metals involves direct electron transfer from the metal to a bond in the lipids and is the simplest mechanism for metal catalysis. Electron transfer to methyl linoleate is exothermic (AH= 62.8kJ, ISkCal), so is probably the dominant initiation mechanism with lipids (23, 27). Ab initio hpid radicals are formed directly by removing an electron from a double bond (Reaction 2) (28, 29) or, more generally, from the C H bond of any labile H in lipid molecules (e.g., allylic hydrogens) (Reaction 3), or via subsequent secondary hydrogen abstraction reactions, as designated in the bracketed reactions. 

In 1972, Parshall used an ionic liquid for the first time for the immobilization of a transition metal catalyst in a biphasic reaction set-up [7]. He described the hydrogenation of CC-double bonds with PtCl2 dissolved in tetraethylammonium chloride associated with tin dichloride ([Et4N][SnCl3], m.p. 78 °C) at temperatures between 60 and 100 °C. A substantial advantage of the molten salt medium [over conventional organic solvents]. .. is that the product may be separated by decantation or simple distillation . The use of ionic liquids as novel media for transition metal catalysis started to receive increasing attention when in 1992 Wilkes reported on the synthesis of... 

The addition of silicon hydrides to nitriles occurs under the influences of noble metal catalysis, the most effective being RuCls n-H20 . Both single and double insertions occur, with one or two silicons attaching to nitrogen. (C2H5)3SiH reacts with isocyanate in the presence of palladium on charcoal at 80 C . ... 

Previously in Chapter 12 we have seen several examples of cydization reactions that have involved transition metal catalysis. In Chapter 11, we introduced Mo- and Ru-catalyzed RCM as a means of converting acyclic dienes, alkene-alkynes, and dialkynes into rings containing carbon-carbon double and triple bonds. Section 12-5 will cover a few cases where organotransition metal complexes effectively promote the construction of rings where two or more C-C bond connections occur during the same transformation. Some examples will be extensions of reactions already covered, whereas others will entail new chemistry. 

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