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Active acylamino acrylic acid

Asymmetric hydrogenationRh(I) complcxed with (R)- or (S)-l catalyzes the asymmetric hydrogenation of prochiral a-(acylamino)acrylic acids, R CHC—C-(COOH)NHCOR2, to optically active derivatives of (R)- or (S)-alanine (85 100% ee). [Pg.36]

Asymmetric Hydrogenation. Asymmetric hydrogenation with good enantio-selectivity of unfunctionalized prochiral alkenes is difficult to achieve.144 145 Chiral rhodium complexes, which are excellent catalysts in the hydrogenation of activated multiple bonds (first, in the synthesis of a-amino acids by the reduction of ol-N-acylamino-a-acrylic acids), give products only with low optical yields.144 146-149 The best results ( 60% ee) were achieved in the reduction of a-ethylstyrene by a rhodium catalyst with a diphosphinite ligand.150 Metallocene complexes of titanium,151-155 zirconium,155-157 and lanthanides158 were used in recent studies to reduce the disubstituted C—C double bond with medium enantioselectivity. [Pg.639]

Rhodium-BisP and -MiniPHOS catalysts are capable of high enantioselective reductions of dehydroamino acids in 96-99.9% ee.109 A variety of aryl enamides give optically active amides with 96-99% ee with the exception of ort/jo-substituted substrates.111 Despite the high enantio-selectivity, the rate of reaction in this transformation is slow. Rhodium-BisP and -MiniPHOS catalysts perform excellently in the asymmetric reduction of ( >P-(acylamino)acrylates to the corresponding protected-P-amino esters in 95-99% ee.112 Within the family of BisP and MiniPHOS, the ligands that contain t-Bu groups were found to be the most effective in a variety of asymmetric hydrogenations. [Pg.207]


See other pages where Active acylamino acrylic acid is mentioned: [Pg.8]    [Pg.173]    [Pg.9]    [Pg.198]    [Pg.9]    [Pg.11]    [Pg.861]    [Pg.925]    [Pg.6]    [Pg.227]    [Pg.218]   
See also in sourсe #XX -- [ Pg.81 , Pg.813 ]




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