Acetophenone solid support

In a more recent study, Westman and Lundin have described solid-phase syntheses of aminopropenones and aminopropenoates en route to heterocycles [32], Two different three-step methods for the preparation of these heterocycles were developed. The first method involved the formation of the respective ester from N-pro-tected glycine derivatives and Merrifield resin (Scheme 7.12 a), while the second method involved the use of aqueous methylamine solution for functionalization of the solid support (Scheme 7.12 b). The desired heterocycles were obtained by treatment of the generated polymer-bound benzylamine with the requisite acetophenones under similar conditions to those shown in Scheme 7.12 a, utilizing 5 equivalents of N,N-dimethylformamide diethyl acetal (DMFDEA) as reagent. The final... 

Fig. 2.13 Ketone reduction of unprecedented efficiency, demonstrated with acetophenone as substrate (a) original BINAP-DIPEN run (b) using a 4,4 -disubstituted BINAP motif as catalyst (c) operating under transfer hydrogenation conditions in H2O and a catalyst on a solid support.

Katritzky et al. [387] have presented a synthesis of 3,4,6-trisubstituted pyrid-2-ones starting with solid support-bound acetophenone, which was deprotonated with NaOCHs to give the corresponding enolate. The latter was condensed with various benzaldehydes to give the resin-bound chalcones [388], which then can react with benzotriazolyl acetamides [389] to give 3,4,6-trisubstituted pyrid-2-ones (Scheme 104). 

Very recently, a unique example of heterogeneous chiral Rh catalyst has emerged, in which the Rh complex 140 was immobilised at the surface of glass plates as solid support, and used in the ATH of aromatic ketones in aqueous medium [115]. Although conversions and ee values reached around 90 %, the recyclability of this catalyst was poor, since the conversion for the reduction of acetophenone decreased rapidly from 99 to 25 % in the 2nd cycle (Fig. 39). 

Bimetallic catalysts can be obtained by surface organometallic chemistry on metals. These catalysts are prepared by the controlled reaction under hydrogen between tetra n-butyl tin and silica supported rhodium particles. For a given amount of tin fixed, these solids exhibit increasing activities and selectivities for the conversion of acetophenone to phenylethanol. 

The aldol condensation of benzaldehyde with acetophenone has been used to compare hydrated hydrotalcites with many solids claimed to be strong solid bases-KF and KNO3 supported on alumina, X zeolites containing excess Cs or Mg, and lanthanum oxide. Only hydrated HDT and KF/AI2O3 could be used to perform this reaction at 273 K-HDT with 100% selectivity for chalcone and KF with lower selectivity, because of secondary Michael addition of the chalcone to acetophenone. The other solids were inactive, but could induce comparable conversions at 423 K. 

Despite the importance of this reaction for the synthesis of chiral amines and amino acids, no effective solid catalyst is yet available [3]. There are two instances where 26 % ee was achieved (Fig. 9), but results with silk-supported Pd are difficult to reproduce, and in the hydrogenation of acetophenone oxime and pyruvic acid oxime stoichiometric amounts of chiral auxiliary were used [21,49]. The latter reaction was also extremely slow - only 15 % yield of alanine was obtained in 45 h. Efficient enantioselective hydrogenation of imines and oximes apparently remains a challenge for future development. 

An efficient way for microwave-assisted reduction of liquid and solid ketones using sodium borohydride without solvent has also been reported. An excess amount of NaBH without alumina or any support was used for die reduction of acetophenone and the yield of the product was 81% under microwave irradiation. It was concluded that the powder of excess NaBH disperses the aggregation of ketone and made a useful contact successfully to provide an efficient reaction, but in case of benzophenone, the reduction needs more time and NaBH to complete die reaction. This lower conversion may be due to some steric reasons (Chen et al., 1999). 

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