Transfer hydrogenation of acetophenone

Ionic liquids have also been applied in transfer hydrogenation. Ohta et al. [110] examined the transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in the ionic liquids [BMIM][PF6] and [BMIM][BF4]. These authors compared the TsDPEN-coordinated Ru(II) complexes (9, Fig. 41.11) with the ionic catalyst synthesized with the task-specific ionic liquid (10, Fig. 41.11) as ligand in the presence of [RuCl2(benzene)]2. The enantioselectivities of the catalyst immobilized by the task-specific ionic liquid 10 in [BMIM][PF6] were comparable with those of the TsDPEN-coordinated Ru(II) catalyst 9, and the loss of activities occurred one cycle later than with catalyst 9. 

Table 41.15 Recycling of 9- and 10-Ru in the asymmetric transfer hydrogenation of acetophenone with the azeotrope in [BMIM][PF6] [110].

Scheme 6-51. Asymmetric transfer hydrogenation of acetophenone in the presence of 119. Reprinted with permission by Am. Chem. Soc., Ref. 112.

Ruthenium-catalysed asymmetric transfer hydrogenation of acetophenone 133... 

To specify the position and the nature of the transferred hydride, the reaction was performed with 2-propanol-dj as solvent/donor, sodium 2-propylate as base and Fe3(CO)12/PPh3/TerPy as catalyst under optimized conditions. In the transfer hydrogenation of acetophenone a mixture of two deuterated 1-phenylethanols was obtained (Scheme 4.7, 9a and 9b). The ratio between 9a and 9b (85 15) indicated a specific migration of the hydride, albeit some scrambling was detected. However, the incorporation is in agreement with the monohydride mechanism, implying the formation of metal monohydride species in the catalytic cycle. 

S. Laue, L. Greiner J. Woltinger, and A. Liese, Continuous application of chem-zymes in a membrane reactor asymmetric transfer hydrogenation of acetophenone, Adv. Synth. Catal. 2001, 343, 711-720. 

Dissymmetric ferrocenyldiphosphines have been synthesized from (R)-(+)-N, N -dimethylaminoethylferrocene. The diphosphines have been used as ligands in asymmetric transfer hydrogenation of acetophenone in the presence of ruthenium catalysts.297 Asymmetric transfer hydrogenation of a,/S-unsaturated aldehydes with Hantzsch dihydropyridines and a catalytic amount of MacMillan imidazolidinone salt (12) leads to the saturated carbonyl compounds in high yields and excellent chemo-and enantio-selectivities.298 ... 

A ruthenium complex containing a novel imidazolium salt moiety catalyses the asymmetric transfer hydrogenation of acetophenone derivatives, with a formic acid- triethylamine azeotropic mixture in an ionic liquid, [bmim][PF6]. The yields and ee are excellent.308... 

Scheme 3.13 Transfer-hydrogenation of acetophenone with HCOOH/NEt3 as hydrogen source...

A method for the monoarylation of (15,25)-l,2-diaminocyclo-hexane by means of palladium-catalyzed aromatic amination has been recently described (eq 13). The resulting new ligands were tested in the catalytic asymmetric transfer hydrogenation of acetophenone. 

Gladiali, S., Pinna, L., Delogu, G., De Martin, S., Zassinovich, G., Mestroni, G. Optically active phenanthrolines in asymmetric catalysis. III. Highly efficient enantioselective transfer hydrogenation of acetophenone by chiral rhodium/3-alkyl phenanthroline catalysts. Tetrahedron Asymmetry 990, 1, 635-648. 

A chiral diaminodiphosphine ligand was attached onto poly(acrylic acid) through an amide linkage. The ruthenium(II) complex of the resultant polymeric ligand (169) was then applied to the asymmetric transfer hydrogenation of acetophenone in 2-propanol (Scheme 3.51) [101]. (S)-l-phenylethanol was obtained in 95% yield with 96% ee by using 158. 

Enantioselective Catalysis in Ionic Liquids 245 Table 7.6 Asymmetric transfer hydrogenation of acetophenone in ionic liquids. 

Scheme 6 Asymmetric transfer hydrogenation of acetophenone derivatives by Ru precatalysts (S,S)-9 and 10 with tetradentate ligands " ...

Scheme 4 Catalytic cycle for the Ru-catalyzed transfer hydrogenation of acetophenone and reduction of the Ru-catalyst by formate to form the Ru-hydride RuH...

Fig. 5.3-10 Ru-complex and task specific ionic liquid for the transfer hydrogenation of acetophenone derivatives using a formic acid-triethylamine azeotropic mixture.

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