Chelating Diphosphines That Contain a Rhenium Stereocenter in the Backbone: Applications in Rhodium-Catalyzed Enantioselective Ketone Hydrosilylations and Alkene Hydrogenations
2002; American Chemical Society; Volume: 21; Issue: 20 Linguagem: Inglês
10.1021/om020432d
ISSN1520-6041
AutoresKlemenz Kromm, Philip L. Osburn, John A. Gladysz,
Tópico(s)Organoboron and organosilicon chemistry
ResumoRhodium chelate complexes of the title diphosphines, ((S)-5, n = 0; (S)-6, n/R = 1/H; (SReSC)- and (SReRC)-7, n/R = 1/Ph), are catalyst precursors (1.0 mol %, 24−26 °C) for additions of Ph2SiH2 to the ketones PhCOCH2R (R = H, CH3, CH2CH3, CH2CH2Cl; 93−77% conversions). Hydrolyses give the alcohols (R)-HOCH(Ph)CH2R in 83−60% isolated yields; configurations correlate with the relative rhenium configurations of the catalysts. The ee values with (S)-6 (63/62/60/92%) exceed those of (S)-5 (44/38/47/48%); ee values of (SReRC)-7 (41/46/62/58%) are higher than those of the diastereomer (SReSC)-7 (23/11/15/35%). The alkenes (Z)-RCHC(NHCOCH3)CO2R' (R/R' = H/H, Ph/H, Ph/CH3) and H2 (1 atm) react in the presence of (SReSC)- and (SReRC)-7 (0.5 mol %, 30 °C) to give the protected amino acids RCH2CH(NHCOCH3)CO2R' in 85−92% yields. The ee values with (SReSC)-7 (37/62/61%) are lower than those found earlier for (S)-6 (62/72/65%) or (S)-5 (92/93/88%), with S enantiomers dominant in all cases. Surprisingly, (SReRC)-7 gave much higher ee values (93/94/97%), but with R enantiomers dominant. Hence, the carbon stereocenter of 7 controls the product configuration.
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