Ketones rhodium catalysis

Under rhodium catalysis, hydridosilanes add to a,(3-unsaturated ketones in a 1,4 manner to produce silyl enol ethers (Equation Si3.3). 

Cyclopropyl ketones are readily isomerized to dihydrofuran derivatives thermally or under catalytic conditions.For example, cyclopropyl ketones 2 and 4 yield dihydrofurans 3 and 5, respectively, thermally or under rhodium catalysis. Such rearrangements occur normally under acid catalysis whereas thermolysis favors the vinylcyclopropane to cyclopentene rearrangement, except for highly functionalized (R = SOjPh) cyclopropanes. 

Rhodium Catalysts. In the early stage of developing rhodium catalysis for intramolecular cyclopropanation, Rh2(OAc>4 was widely used in the construction of bridged or fused polycyclic molecules. For instance, it was used as a catalyst to obtain a tricyclic ketone used as an intermediate of eucalyptol in good... 

That Rh-allyl complexes can also act as nucleophiles in addition to aldehydes has been demonstrated by Oshima et al. in 2006 [198]. Retro-aUylation of the homoallyl alcohol 191 under rhodium catalysis generates a nucleophilic aUylrhodium species that reacts with aldehydes 190 to give the corresponding secondary alcohols 192 in situ (Scheme 12.94). Subsequent isomerization of these alcohols proceeds under the reaction conditions to furnish the corresponding saturated ketones 193 in modest to good yields. 

The conjugate addition of HSiR3 onto a, y -unsaturated ketones is of particular interest in synthesis. Silylenolates are thus easily obtained and can be further used. Cobalt catalysis has been recommended as a particularly convenient method for the preparation of such silylenolates [82]. Earlier reports refer to rhodium catalysis [82], and palladium and nickel [83] catalysts. 

Whereas platinum-catalysed reduction of acid chlorides with triethyl-silane gives aldehydes, Eaborn has shown that rhodium catalysis can give predominantly ketones. a-Ketophosphonate esters, readily available from the action of carboxylic acid chlorides on trialkyl phosphites, are reduced by sodium borohyffiride to the ester (123), which fragments to the... 

Too et al. demonstrated that isoquinoUne synthesis can be conducted by coupling of aryl ketone O-acyloxime 110 with 2c under rhodium catalysis without addition of any external oxidant (Scheme 25.54) [51]. Similar annulation of aryl ketone O-benzyloximes under nickel catalysis was also disclosed by Yoshida et al. [52]. 

Electron spin resonance (ESR) signals, detected from phosphinated polystyrene-supported cationic rhodium catalysts both before and after use (for olefinic and ketonic substrates), have been attributed to the presence of rhodium(II) species (348). The extent of catalysis by such species generally is uncertain, although the activity of one system involving RhCls /phosphinated polystyrene has been attributed to rho-dium(II) (349). Rhodium(II) phosphine complexes have been stabilized by steric effects (350), which could pertain to the polymer alternatively (351), disproportionation of rhodium(I) could lead to rhodium(II) [Eq. (61)]. The accompanying isolated metal atoms in this case offer a potential source of ESR signals as well as the catalysis. 

Similarly, ketimines (benzylimines of aromatic ketones) undergo the rhodium-catalyzed ortho-alkenylation with alkynes to give or/ o-alkenylated aromatic ketones after hydrolysis.61 This method is applied to an efficient one-pot synthesis of isoquinoline derivatives by using aromatic ketones, benzylamine, and alkynes under Rh catalysis (Equation (55)). 

L. V. Dinh, J. Gladysz, Transition Metal Catalysis in Fluorous Media Extension of a New Immobilization Principle to Biphasic and Monophasic Rhodium-Catalyzed Hydrosilylations of Ketones and Enones , Tetrahedron Lett. 1999, 40,8995. 

Abstract The purpose of this chapter is to present a survey of the organometallic chemistry and catalysis of rhodium and iridium related to the oxidation of organic substrates that has been developed over the last 5 years, placing special emphasis on reactions or processes involving environmentally friendly oxidants. Iridium-based catalysts appear to be promising candidates for the oxidation of alcohols to aldehydes/ketones as products or as intermediates for heterocyclic compounds or domino reactions. Rhodium complexes seem to be more appropriate for the oxygenation of alkenes. In addition to catalytic allylic and benzylic oxidation of alkenes, recent advances in vinylic oxygenations have been focused on stoichiometric reactions. This review offers an overview of these reactions... 

Some other catalytic events prompted by rhodium or ruthenium porphyrins are the following 1. Activation and catalytic aldol condensation of ketones with Rh(OEP)C104 under neutral and mild conditions [372], 2. Anti-Markovnikov hydration of olefins with NaBH4 and 02 in THF, a catalytic modification of hydroboration-oxidation of olefins, as exemplified by the one-pot conversion of 1-methylcyclohexene to ( )-2-methylcycIohexanol with 100% regioselectivity and up to 90% stereoselectivity [373]. 3. Photocatalytic liquid-phase dehydrogenation of cyclohexanol in the presence of RhCl(TPP) [374]. 4. Catalysis of the water gas shift reaction in water at 100 °C and 1 atm CO by [RuCO(TPPS4)H20]4 [375]. 5. Oxygen reduction catalyzed by carbon supported iridium chelates [376]. - Certainly these notes can only be hints of what can be expected from new noble metal porphyrin catalysts in the near future. 

A reaction between a-diazo ketones and a,(1-unsaturated aldehydes under rhodium(ll)-catalysis provides a route to epoxy-bridged tetrahydropyran-4-ones <2002JOC8019>. This methodology allows entry to functionalized spiro-dioxa-bridged polycyclic frameworks <2002TL3931, 2003T8117>. 

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. 

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