Amido ketones

Potassium and sodium borohydride show greater selectivity in action than lithium aluminium hydride thus ketones or aldehydes may be reduced to alcohols whilst the cyano, nitro, amido and carbalkoxy groups remain unaffected. Furthermore, the reagent may be used in aqueous or aqueous-alcoholic solution. One simple application of its use will be described, viz., the reduction of m-nitrobenzaldehyde to m-nitrobenzyl alcohol ... 

The P-halo ketone intermediates formed in the foregoing reactions arise from the capture of carbocationic intermediates by halide of the gegenions. In some cases, solvents such as acetonitrile can act as the competing nucleophilic species. For example, P-amido ketones could be obtained by the acylation of alkenes in acetonitrile (172). 

Reaction of dpp-bian with Mg in THF for 30 min reflux gives complex 87 (Ar = 2,6-diisopropylphenyl) which undergoes oxidative addition via m-bond metathesis with PhC=CH to give the black alkynyl amido complex 88. The insertion reaction of 88 with Ph2CO in EtzO yields complex 89. Unexpectedly, hydrogen abstraction to give the radical anion occurs simultaneously with ketone insertion.268... 

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

Scheme 3.12 Enantioselective hydrogenation of a ketone by transfer from iso-propanol catalyzed by the hydride complex RuH( 6-arene)(NH2CHPhCHPhNTs) and the amido complex Ru(r 6-arene)(NHCHPhCHPhNTs) [94].

Most UV absorption bands correspond to transitions of electrons from ra->7i, or n o molecular orbitals. Besides aromatic compounds, organic functional groups such as carbonyl, carboxylic, amido, azo, nitro, nitroso, and ketone groups have absorbance in the UV region. 

Fig. 6.25. Simplified mechanism of two degradation reactions between peptides and reducing sugars occurring in solids, a) Maillard reaction between a side-chain amino (or amido) group showing the formation of an imine (Reaction a), followed by tautomerization to an enol (Reaction b) and ultimately to a ketone (Reaction c). Reaction c is known as the Amadori rearrangement (modified from [8]). b) Postulated mechanism of the reaction between a reducing sugar and a C-terminal serine. The postulated nucleophilic addition yields an hemiacetal (Reaction a) and is followed by cyclization (intramolecular condensation Reaction b). Two subsequent hydrolytic steps (Reactions c and d) yield a serine-sugar conjugate and the des-Ser-peptide...

Inspired by the reaction mechanism of Noyori s catalytic enantioslective transfer hydrogenation of ketones (32) using a chiral Ru-amido complex 31, Dcariya et al. reported that 31 can also function as a unique Bronsted base-Bronsted acid catalyst... 

This method accommodates aryl aldehydes with both electron-deficient and electron-rich aryl substitutents. Acetaldehyde is also a competent couphng partner, providing the corresponding amido ketone in 62% yield. Acyl substitution of the tosyl amide varies to include hydrogen, methyl, tert-butoxy, and phenyl producing the desired a-amido ketones in moderate to high yields. Expansion of this methodology to synthesize di- and tri-substituted imidazoles was reported by Murry and co-workers (Scheme 7) [54]. 

Alternatively, when the reaction is carried out at 140 °C, the thermodynamically preferred amido ketone is formed (Scheme 3.11b), even though the less reactive ester group of the keto ester is the locus of the initial nucleophilic attack. Ring closure of the amino ketone then affords the 4-quinolone. 

Figure 7.46 Main methods for the synthesis of amido trifluoromethyl ketones.

The C=C bond in a 5-(alkylidene)oxazoline 644 is activated for electrophilic reactions similar to that in analogous vinyl acetates. Rohm Haas researchers exploited this property to prepare chloromethyl ketone fungicides 646 (Scheme 8.203). The overall process constitutes an indirect chlorination of a-amido ketones since the 5-(vinylidene)oxazolines were prepared from a-amido ketones. 

Toluenesulfonyl-amido-2-phenylethyl chloromethyl ketone (TPCK)... 

Treatment of an a-amino acid with an anhydride in the presence of pyridine, known as the Dakin-West reaction,[1431 gives access to a racemic a-amido ketone.1 44 1451 The mechanism involves formation of an oxazolinone (98)J146 In the modified Dakin-West reaction, the oxazolinone is reacted with an acid chloride (Scheme 33)J136 139] Due to the rapid epimer-ization of the oxazolinones, a diastereomeric mixture of product 99 is obtained. No detailed protocol has been published so far for the modified Dakin-West synthesis applied to (oxomethyleneamino) peptides, but the procedure is adapted from that already reported for (oxomethylene) peptides containing the tp[CO-CH2] link.1147 ... 

Selective reduction of carbonyl groups.1 Heterogeneous reduction of carbonyl groups by triethoxysilane with CsF (or KF) as catalyst is highly selective, the reactivity order being aldehyde > ketone > ester. Double bonds, nitro, halo, and amido groups are inert to this reagent. 

A further formal total synthesis95 of aspidospermine is provided by a new preparation of Stork s tricyclic amido-ketone (152). The hydrolulolidine system in (152) was neatly constructed by cheletropic expulsion of sulphur dioxide from the amide-sulphone (153), followed by an internal Diels-Alder reaction. 

---