Chiral Bis(oxazoline) Ligand Embedded into Polysiloxane Gel
dard solutions, of which the Cu concentration was in a range from 10 ppb
to 200 ppb, were used for calibration. l-Menthyl-2,2-dimethylcyclopro-
pane-1-carboxylate:[16] IR (neat): n˜ =2953, 2927, 2869, 1719, 1455, 1397,
1267, 1168, 1150, 1092, 830, 759 cmÀ1; 1R isomer: 1H NMR (396 MHz,
CDCl3): d=0.75 (d, J=6.8 Hz, 3H, CH3 of menthyl), 0.89 (d, J=6.8 Hz,
3H, CH3 of menthyl), 1.16 (d, J=6.8 Hz, 3H, CH3 of menthyl), 1.46 (dd,
J=7.7, 5.3 Hz, 1H), 4.69 ppm (td, J=11.1, 4.3 Hz, 1H, CO2CH);
13C NMR (99.5 MHz, CDCl3): d=16.5, 19.0, 20.7, 21.6, 22.1, 22.8, 23.7,
26.5, 27.1, 27.4, 31.5, 34.4, 41.2, 47.2, 74.0 (CO2C), 172.3 ppm (C=O);
GLC (TC-1, 30 m, detection FID, column temp.: 120 to 1808C at
18CminÀ1), tR =17.2 min (1S), 17.5 min (1R).
Experimental Section
All reactions were carried out under a nitrogen or argon atmosphere.
Anhydrous solvents (THF, hexane, and dichloromethane) were pur-
chased from Kanto Chemical Co., Ltd., and used as received. THP was
purchased from Tokyo Chemical Industry Co., Ltd., and distilled under
an inert atmosphere from sodium/benzophenone prior to use. Diethylma-
lonimidate hydrochloride, (l)-tert-leucinol, allyl bromide, and 1,5-hexa-
diene were purchased from Tokyo Chemical Industry Co., Ltd. Karstedtꢁs
catalyst in 0.1m xylene solution was purchased from Aldrich Chemical
Co. Sodium hydride was purchased from Kishida Chemical Co., Ltd.
PolyACHTUNGTRENNUNGmethylhydrosiloxane (PMHS, n=25) was purchased from AZmax
Co. Ltd. 1H, 13C, and 29Si NMR spectra were measured on JEOL ECA
400 (396 MHz and 400 MHz) and ECA 600 (600 MHz) spectrometers.
1
Chemical shifts for H NMR are described in parts per million downfield
from tetramethylsilane as an internal standard (d=0 ppm) in CDCl3,
unless otherwise noted. Chemical shifts for 13C NMR are expressed in
parts per million in CDCl3 as an internal standard (d=77.1 ppm), unless
otherwise noted. Chemical shifts for solid-state 13C and 29Si NMR spectra
are described in parts per million downfield from hexamethylbenzene
(d=132 ppm) and polydimethylsilane (d=À34 ppm) as an external stan-
dard. IR spectra were measured on a JASCO FT/IR-4200 spectrometer.
Gas chromatography (GC) analyses were performed on a Shimadzu GC-
17A gas chromatograph equipped with TC-1 and TC-17 (30 m) columns.
High-performance liquid chromatography (HPLC) analyses were per-
formed with a JASCO PU-2080 HPLC pump, UV-2075 UV/Vis detector
using a Daicel CHIRALCEL OD-H column. ICP-MS analysis was per-
formed at the Analytical Center in Institute for Materials Chemistry and
Engineering, Kyushu University. Analytical thin-layer chromatography
(TLC) was performed on glass plates precoated with silica gel (Merck,
Kieselgel 60 F254, layer thickness 0.2 mm). Visualization was accom-
plished by UV light (254 nm), anisaldehyde, and phosphomolybdic acid.
l-Menthyl diazoacetate was prepared by the literature method.[14]
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Keywords: copper
·
cyclopropanation
·
heterogeneous
catalysis · N ligands · polysiloxane gels
[1] Comprehensive reviews: a) R. Noyori, Asymmetric Catalysis in Or-
ganic Synthesis, Wiley Interscience, New York, 1994; b) Comprehen-
sive Asymmetric Catalysis, Vols. I–III (Eds: E. N. Jacobsen, A.
Pfaltz, H. Yamamoto), Springer, Berlin, 1999; c) Catalytic Asymmet-
ric Synthesis, 2nd ed. (Ed.: I. Ojima), Wiley-VCH, New York, 2000;
d) Handbook of Asymmetric Heterogeneous Catalysis (Eds.: K.
Ding, Y. Uozumi),Wiley-VCH, Weinheim, 2008.
Typical procedure for the [Cu
lyzed cyclopropanation of l-menthyl Diazoacetate with styrene (Table 1,
entry 4): To a suspension of styrene (20 mmol) and [Cu(OTf)2A{(S,S)-tBu2-
ACHTUNGTNERNUG(OTf)2ACHTUNGTREN{NUGN (S,S)-tBu2-DABox}][Pt]@Si-cata-
A
CHTUNGTRENNUNG
[2] Recent reviews: a) C. A. McNamara, M. J. Dixon, M. Bradley,
[3] a) I. F. J. Vankelecom, D. Tas, R. F. Parton, V. Van de Vyver, P. A.
Tas, K. B. M. Janssen, P.-P. Knops-Gerrits, P. A. Jacobs, J. Mol. Catal.
A 1996, 113, 283–292; c) I. Vankelecom, A. Wolfson, S. Geresh, M.
2408; d) A. Wolfson, S. Janssens, I. Vankelecom, S. Geresh, M. Got-
Guedes, T. C. O. Mac Leod, M. C. A. F. Gotardo, M. A. Schiavon,
N. B. Bowden, J. Organomet. Chem. 2006, 691, 5278–5288.
DABox}][Pt]@Si catalyst ([Cu]=2.5 mol%) in dichloromethane (1 mL)
was added a solution of l-menthyl diazoacetate (44.9 mg, 0.2 mmol) in di-
chloromethane (2 mL). After the reaction completed, the insoluble [Cu-
ACHTUNGTRENNUNG(OTf)2ACHTUNGTRENNUNG{(S,S)-tBu2-DABox}][Pt]@Si catalyst was removed by filtration.
The residual gel was washed with ether, and the filtrate was concentrated
under reduced pressure. Purification of the residue by silica gel chroma-
tography gave l-menthyl-2-phenylcyclopropane-1-carboxylate[15] in 98%
yield. IR (neat): n˜ =2953, 2925, 2868, 1719, 1455, 1403, 1265, 1175, 1151,
754, 696 cmÀ1; 1R,2R isomer : 1H NMR (396 MHz, CDCl3): d=0.77 (d,
J=6.8 Hz, 3H, CH3 of menthyl), 0.89 (d, J=7.2 Hz, 3H, CH3 of menth-
yl), 0.92 (d, J=6.8 Hz, 3H, CH3 of menthyl), 4.72 ppm (td, J=10.6,
4.3 Hz, 1H, CO2CH); 13C NMR (99.5 MHz, CDCl3): d=16.5, 17.1, 20.9,
22.1, 23.5, 24.4, 26.0, 26.3, 31.5, 34.4, 41.1, 47.2, 74.5 (CO2C), 140.4 (Cipso),
173.0 ppm (C=O); 1S,2S isomer: 1H NMR (396 MHz, CDCl3): d=
4.47 ppm (td, J=11.1, 4.3 Hz, 1H, CO2CH); 1R,2S isomer: 1H NMR
(396 MHz, CDCl3): d=4.41 (td, J=10.6, 4.3 Hz, 1H, CO2CH); 13C NMR
(99.5 MHz, CDCl3): d=16.1, 20.8, 22.0, 22.5, 23.3, 25.6, 26.0, 31.3, 34.2,
40.6, 46.9, 74.0 ppm (CO2C); GLC (TC-1, 30 m, detection FID, column
temp.: 2008C), tR =10.6 min (1S,2R), 10.9 min (1R,2S), 12.2 min (1R,2R),
12.7 min (1S,2S).
[4] a) Y. Motoyama, K. Mitsui, T. Ishida, H. Nagashima, J. Am. Chem.
1574–1576; d) S. Hanada, E. Tsutsumi, Y. Motoyama, H. Nagashi-
Recycling experiments and ICP-MS analysis of the product (Table 2):
After the reaction of isobutylene and l-menthyl diazoacetate with [Cu-
ACHTUNGTRENNUNG(OTf)2ACHTUNGTRENNUNG{(S,S)-tBu2-DABox}][Pt]@Si ([Cu]=7.3 mol%) described as above,
[5] a) Y. Motoyama, M. Abe, K. Kamo, Y. Kosako, H. Nagashima,
[6] Reviews: a) A. K. Ghosh, P. Mathivanan, J. Cappiello, Tetrahedron:
Yao, H. Audrain, J. Thorhauge, Acc. Chem. Res. 1999, 32, 605–613;
the recovered catalyst was dried under reduced pressure and subjected to
a further run of cyclopropanation of isobutylene and l-menthyl diazoace-
tate. The copper content in the l-menthyl-2,2-dimethylcyclopropane-1-
carboxylate was determined by ICP-MS analysis: the crude product ob-
tained by the above procedure was dissolved in concentrated HCl
(30 mL), and the solution was stirred at 708C overnight. Then the solu-
tion was diluted with 0.048m HNO3. The measurement was performed
using this solution. The copper content was calibrated with a commercial-
ly available standard reagent (KANTO Chemical Co. INC.: copper
atomic absorption standard solution, 999 mgLÀ1 Cu in HNO3); five stan-
Chem. Asian J. 2011, 6, 78 – 82
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
81