References and Notes
1a
Andersson PG.
Munslow IJ.
Modern Reduction Methods
Wiley-VCH;
New
York:
2008.
1b
Burke SD.
Danheiser RL.
Handbook of Reagents for Organic Synthesis,
Oxidizing and Reducing Agents
John Wiley and Sons;
Chichester:
1999.
For reviews, see:
2a
Bullock RM.
Angew. Chem. Int. Ed.
2007,
46:
7360
2b
Enthaler S.
Junge K.
Beller M.
Angew.
Chem. Int. Ed.
2008,
47:
3317
2c
Riant O.
Mostefi N.
Courmarcel J.
Synthesis
2004,
2943
2d For papers: Shaikh NS.
Enthaler S.
Junge K.
Beller M.
Angew. Chem.
Int. Ed.
2008,
47:
2497
3a
Mimoun H.
J. Org. Chem.
1999,
64:
2582
3b
Mimoun H.
de Saint Laumer JY.
Giannini K.
Scopelliti R.
Floriani C.
J. Am. Chem. Soc.
1999,
121:
6158
4a
Bette V.
Mortrex A.
Lehmann CW.
Carpentier
J.-F.
Chem.
Commun.
2003,
332
4b
Bette V.
Mortorex A.
Savoia D.
Carpentier J.-F.
Tetrahedron
2004,
60:
2837
5
Mastranzo VM.
Quintero K.
de Parrodi CA.
Juaristi E.
Walsh PJ.
Tetrahedron
2004,
60:
1781
6
Ushio H.
Mikami K.
Tetrahedron Lett.
2005,
46:
2903
7
Gérard S.
Pressel Y.
Riant O.
Tetrahedron:
Asymmetry
2005,
16:
1889
8
Bandini M.
Melucci M.
Piccinelli F.
Sinisi R.
Tommasi S.
Umani-Ronchi A.
Chem. Commun.
2007,
4519
Hydrosilylation of imines with chiral
zinc catalysts:
9a
Ireland T.
Fontanet F.
Tchao G.-G.
Tetrahedron
Lett.
2004,
45:
4383
9b
Park B.-M.
Mun S.
Yun J.
Adv. Synth.
Catal.
2006,
348:
1029
10a
Nishiyama H.
Furuta A.
Chem.
Commun.
2007,
760
10b
Furuta A.
Nishiyama H.
Tetrahedron Lett.
2008,
49:
110
For compound 6,
see:
11a
Albano VG.
Bandini M.
Melucci M.
Monari M.
Piccinelli F.
Tommasi S.
Umani-Ronchi A.
Adv. Synth. Catal.
2005,
347:
1507
11b
Albano VG.
Bandini M.
Barbarella G.
Melucci M.
Monari M.
Piccinelli F.
Tommasi S.
Umani-Ronchi A.
Chem.
Eur. J.
2006,
12:
667
12
Typical Procedure
for Hydrosilylation of Methyl Biphenyl-4-yl Ketone (1)
Zinc
acetate (9.2 mg, 0.05 mmol; Wako 260-01881, lot LTM1219) and the
ketone (196 mg, 1.0 mmol) were placed in a flask. Under an argon
atmosphere, absolute THF (3.0 mL) was added at r.t. The mixture
was stirred for 10 min at 65 ˚C, and (EtO)2MeSiH
(320 µL, 2.0 mmol) was then added by a syringe. The mixture
was stirred for 24 h at 65 ˚C. The reaction was
monitored by TLC examination; the ketone was consumed, and the silyl
ether product was observed. At 0 ˚C, aq HCl (2
N, 2 mL) was added to quench the reaction. After stirring for 1
h, the mixture was extracted with EtOAc (3 × 10 mL), and
the extract was washed with brine and aq NaHCO3 and dried
over Na2SO4. After concentration, the residue
was purified by silica gel column chromatography (hexane-EtOAc
as eluent) to give the corresponding desired alcohol 2 (196
mg, 0.99 mmol) in 99%.
Asymmetric
Hydrosilylation of Methyl α-Naphthyl Ketone
Under
the same reaction conditions above described in the typical procedure,
the ligand 7a (27.4 mg, 0.06 mmol) and methyl α-naphthyl
ketone (170 mg, 1.0 mmol) were used to obtain the alcohol 13 (163 mg, 0.95 mmol) in 95% and
92% ee (S); analysis, CHIRALCEL
OJ-H [hexane-2-PrOH (95:5), 0.8 mL min-¹]; t
R (S) = 34.2
min, t
R (R) = 43.5
min.
13
Preparation of
Ligands 7a and 7b
A mixture of (1R,2R)-cyclohexane-1,2-diamine (116 mg, 1.0
mmol), 4-phenylthiophene-2-carbaldehyde (392 g, 2.1 mmol, commercially
available), MgSO4 (2.4 g) in THF (10 mL) was
stirred at r.t. for 40 h. After diluted with EtOAc (10 mL), the
mixture was filtered through Celite and was concentrated to give
white solids (ca. 470 mg). A MeOH solution (15 mL) of the solids
was treated with NaBH4 (392 mg) at r.t. for 18 h. Then,
H2O (15 mL) was added, and the mixture was extracted
with EtOAc. The extract was washed with brine and dried over Na2SO4.
After concentration, the residue was purified by silica gel column
chromatography with hexane-EtOAc to give white solids (265
mg, 0.58 mmol) in 58% yield.
Compound 7a: mp 113-115 ˚C.
IR (KBr): ν = 3100, 3056, 2927, 2853, 1451, 737,
688 cm-¹. ¹H NMR
(300 MHz, CDCl3): δ = 0.91-2.37
(m, 14 H), 3.90-3.94 (m, 2 H), 4.13-4.18 (m, 2
H), 7.24-7.39 (m, 8 H), 7.54-7.57 (m, 4 H). ¹³C (75
MHz, CDCl3): δ = 25.1, 31.6, 45.7,
60.4, 118.8, 123.4, 126.0, 126.7, 128.5, 135.8, 141.3, 145.7. Anal.
Calcd (%) for C28H30N2S2:
C, 73.32; H, 6.59; N, 6.11. Found: C, 72.91; H, 6.69; N, 6.01; [α]D
²9 -17.0
(c 1.00, CHCl3).
Synthesis of Compound
7b
Starting
from 2,6-diisopropylaniline via 2,6-diisopropyl-phenyliodide, 2,6-diisopropylphenyl
boronic acid was prepared. The mixture of the boronic acid (463
mg, 2.25 mmol), 4-bromothiophene-2-carbaldehyde (318 mg, 1.5 mmol,
commercially available), Pd(OAc)2 (3.4 mg), S-Phos (12.7 mg), K3PO4 (650
mg, 3.0 mmol) in toluene (3.0 mL) at 100 ˚C for
24 h. The mixture was diluted with EtOAc and filtered through Celite.
After concentration, the residue was purified by silica
gel column chromatography to give
4-(2′,6′-diisopropylphenyl)thiophene-2-carbaldehyde
(354 mg, 1.3 mmol) in 87%. A mixture of (1R,2R)-cyclohexane-1,2-diamine
(46 mg, 0.4 mmol), thiophene-2-carbaldehyde (218 mg, 0.8 mmol, commercially
available), and MgSO4 (960 mg) in THF (5.0 mL) was stirred
at r.t. for 24 h. After diluted with EtOAc, the mixture was filtered
through Celite and was concentrated to give white solids. A MeOH
solution (10 mL) of the solids was treated with NaBH4 (151
mg) at r.t. for 24 h. Then, H2O (10 mL) was added, and
the mixture was extracted with EtOAc. The extract was washed with brine
and dried over Na2SO4. After concentration,
the residue was purified by silica gel column chromatography with
hexane-EtOAc to give the desired amine 7b (178
mg, 0.284 mmol) in 71% yield.
Compound 7b: oil. IR (film): ν = 3055,
2959, 2927, 2861, 1459, 751, 673 cm-¹. ¹H
NMR (300 MHz, CDCl3): δ = 1.09-1.10
(m, 24 H), 1.15-1.40 (m, 6 H), 1.85 (m, 2 H), 2.23 (m, 2
H), 2.42 (m, 2 H), 2.83 (m, 4 H), 4.00 (d, J = 14.9
Hz, 2 H), 4.19 (d, J = 14.9
Hz, 2 H), 6.82 (s, 2 H), 6.93 (s, 2 H), 7.22-7.27 (m, 4
H), 7.38 (m, 2 H). ¹³C (75 MHz, CDCl3): δ = 24.2, 24.3,
24.5, 24.6, 25.1, 30.3, 30.4, 31.6, 45.5, 60.2, 121.0, 122.1, 126.9,
127.6, 134.4, 139.2, 144.0, 147.4. HRMS-FAB: m/z calcd for C40H55Cl2N2S2
+ [M + H]:
627.3807; found: 627.3805. [α]D
²9 -23.4
(c 1.00, CHCl3).
