Metallation, of aromatic ketones

Metallacyclic complexes. 26 142 Metallation, of aromatic ketones, 26 155 Methane, bromo-, ruthenium, and osmium complexes, 27 201, 205... 

Commonly, transition metals on non-reducible supports are used for the selective hydrogenation of aromatic ketones, with most research to date having been done on Pt-based catalysts. In particular, we will discuss here some interesting results published on this subject. 

As shown in Figure 1.26, a chiral Sm(III) complex catalyzes asymmetric reduction of aromatic ketones in 2-propanol with high enantioselectivity. Unlike other late-transition-metal catalysis, the hydrogen at C2 of 2-propanol directly migrates onto the carbonyl carbon of substrate via a six-membered transition state 26A, as seen in the Meerwein-Ponndorf-Verley reduction. ... 

Catalytic hydrogenation of aromatic ketones was successful over a wide range of catalysts under mild conditions (25°, 1 atm). Of the noble metal family some metals more than others tend to hydrogenolyze the alcohol formed, and/or saturate the ring. Evaluation of some metal catalyst is based on hydrogenation of acetophenone as a representative [35,814]. 

Metal acetylacetonates quench triplet species generated by flash photolysis of aromatic ketones and hydrocarbons.330-333 More recently, these reactions have been studied from a synthetic standpoint. Triplet state benzophenone sensitizes photoreduction of Cu(MeCOCHCOMe)2 by alcohols to give black, presumably polymeric, [Cu(MeCOCHCOMe)] . This reacts with Lewis bases to provide complexes of the type CuL2(MeCOCHCOMe) (L = bipyridyl/2, ethylenediamine/2, carbon monoxide, Ph3P). Disubstituted alkynes yield Cu(C2 R2 XMeCOCHCOMe) but terminal alkynes form CuQR acetylides.334 The bipyridyl complex of copper(I) acetylacetonate catalyzes the reduction of oxygen to water and the oxidation of primary and secondary alcohols to aldehydes and ketones.335... 

An enantioselective metal-free hydrosilylation of aromatic ketones (and also of their imines) employs a quinolyloxazoline (88), which brings about a relatively long-range induction.262... 

A new, metal-free protocol involving (heteroaryl)oxazoline catalysts for the enantioselective reduction of aromatic ketones (up to 94% ee) and ketimines (up to 87% ee) with trichlorosilane has been developed. The reaction is characterized by an unusual, long-ranging chiral induction.The enantiodifferentiation is presumed to be aided by aromatic interactions between the catalyst and the substrate.360 Asymmetric reduction of A-arylketimines with trichlorosilane is catalysed by A-methyl-L-amino acid-derived Lewis-basic organocatalysts with high enantioselectivity (up to 92% ee) 61... 

Samarium metal, in the presence of various additives such as ammonium chloride or bromide, induces reductive dimerizations of aromatic ketones to give 1,2-diols, with some diastereoselectivity, and with some alcohol (i.e. reduced ketone) by-product.164 The syn-selectivity observed in many cases may be due to samarium chelation of the... 

Table 2. Examples of couplings of aromatic ketones with olefins using transition metal catalysts. ...

The number of publications describing new ligands that allow the transfer hydrogenation of aromatic ketones with over 90 % ee has grown in leaps and bounds since 1996 [15]. In these reactions the use of ruthenium [15a-f] and iridium [15g] as the catalytically active metals has recently been augmented by the use of phosphorus-free ligands such as chiral diamines, amino alcohols, and bisthioureas such as 7 [15a,e-g]. A ruthenium-catalyzed transfer hydrogenation with 92 % ee has even been reported for the aliphatic ketone pinacolone (tert-butyl methyl ketone) [16]. 

As before, the enzymatic reduction is the method of choice for the enantioselective reduction of purely aliphatic ketones and only in the case of fert-butyl methyl ketone could the bench mark of 90 % ee be crossed by the transfer hydrogenation and both other catalytic hydrogenation methods. However, substantial success in the hydrogenation of aromatic ketones by transition metal complexes with respect to the enantioselectivity and the activity (TON) strengthens the confidence that further progress is possible, enabling us to use some advantages of these nonenzymatic processes for extended application in the near future, for example in the facilitation of product isolation. 

Reduction of aromatic ketones. It has been generally assumed that metal ammonia reduction of aromatic ketones leads to alcohols, mainly because benzo-phenone (1) is reduced to diphenylmcthanol (2, benzhydrol) by sodium in liquid ammonia. However, Hall and co-workers report that aromatic ketones are reduced,... 

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