Angewandte
Chemie
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solution, suggest that the chemistry observed is occurring in a
heterogeneous fashion.
2005, 102–103, 154; T. Tsoncheva, S. Vankova, O. Bozhkov, D.
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Experimental Section
Preparation of CuII/C: Darco KB (5.00 g, 100 mesh) activated carbon
(25% H2O content) was added to a 100-mL round-bottom flask
containing a stirring bar. A solution of Cu(NO3)2·3H2O (Acros
Organics, Cu content by ICP determination: 127%; 555.7 mg,
2.92 mmol) in deionized H2O (35 mL) was added to activated
carbon, and deionized H2O (40 mL) was added to wash down the
sides of the flask. The flask was purged under argon and stirred
vigorously for 1 min. The flaskwas submerged in an ultrasonic bath
under a positive argon flow for 30 min. The flaskwas attached to an
argon-purged distillation setup and placed in a preheated 175–1808C
sand bath with stirring plate. As the distillation ended, the flask
temperature rises automatically but should be held below 2108C for
an additional 15 min. Upon cooling to room temperature, toluene
(25 mL) was added to wash down the sides of the flask. The flask was
again placed into the hot sand bath until the toluene/H2O azeotrope
had distilled. Once the distillation was finished, the azeotropic
distillation was repeated. Upon cooling to room temperature, the
blacksolid was washed with toluene (2 30 mL) under argon into a
predried (in vacuo) 150-mL coarse-fritted funnel. The toluene
(60 mL) used to wash the Cu/C was removed by rotatary evaporation
and analyzed for any remaining copper. The fritted funnel was turned
upside down under vacuum for 5 h until the Cu/C fell from the frit
into the collection flask. The collection flask was then dried in vacuo
in a preheated 110–1158C sand bath for 18 h. Using these specific
amounts, the catalyst loading was 0.344 mmol CuII/g catalyst, or
2.2 wt.% Cu.
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[13] a) C. Bolm, J.-C. Frison, J. Le Paih, C. Moessner, G. Raabe, J.
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Chem. Soc. 2003, 125, 8779; b) B. H. Lipshutz, J. M. Servesko,
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[17] B. H. Lipshutz, S. Tasler, Adv. Synth. Catal. 2001, 343, 327.
[18] While PMHS purchased from Lancaster and used as received
works well in this chemistry, the material from Acros was
surprisingly ineffective as a source of hydride.
[19] T. Saito, T. Yokozawa, T. Ishizaki, T. Moroi, N. Sayo, T. Miura, H.
Kumobayashi, Adv. Synth. Catal. 2001, 343, 264.
Representative asymmetric hydrosilylation: conversion of iso-
phorone into (R)-3,3,5-trimethylcyclohexanone (Table 2, entry 6):
Cu/C (134.4 mg, 0.05 mmol), NaOPh (24.0 mg, 0.20 mmol), and
DTBM-segphos (2.4 mg, 0.002 mmol) were added to a flame-dried,
argon-purged 10-mL round-bottom flask. Toluene (2 mL) was added
and allowed to stir for 90 min. PMHS (240 mL, 4 mmol HÀ) was then
added dropwise and allowed to stir for 30 min. Isophorone (300 mL,
2 mmol) was added neat and the reaction was allowed to stir at room
temperature until shown to be complete by TLC analysis (3 h; 4:1
hexanes/EtOAc). The reaction mixture was filtered and washed with
Et2O (3 5 mL) to remove the Cu/C. The reaction mixture was
quenched with aqueous NaOH (15 mL, 3m) and allowed to stir at
room temperature for 3 h. The residue was purified by flash
chromatography (4:1 hexanes/EtOAc) to afford the title product
(196.3 mg, 70% yield due to volatility) as a clear oil. Analysis of the
residue by GC showed 98.9% ee by using a Chiraldex-BDM column
with 758C isotherm, Rt = 41.47 (minor) and 44.94 (major) min. The
product matched previously reported spectral data.
Received: September 5, 2005
Published online: January 20, 2006
Keywords: asymmetric catalysis · copper ·
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.
heterogeneous catalysis · hydrosilylation
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Angew. Chem. Int. Ed. 2006, 45, 1259 –1264
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