References and Notes
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First racemic synthesis:
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<A NAME="RG32508ST-17">17</A>
Enantiopure BINOL: 5 g ca. 50 ı [(R)-BINOL, ABCR; (S)-BINOL,
AlfaAesar), 1 kg ca. 900 $ [(R)-
or (S)-BINOL, AK Scientific).
<A NAME="RG32508ST-18">18</A>
Ooi T.
Ohmatsu K.
Maruoka K.
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<A NAME="RG32508ST-19">19</A>
(S)-BINOL
monotriflate (5.59 g, 13.4 mmol) was dissolved in CH2Cl2 (35
mL) and CH2(OMe)2 (35 mL). Then P4O10 (3.93
g, 13.8 mmol, 1.03 equiv) was added within 1 h in 2 portions. The
mixture was stirred at r.t. for 7 h, poured into aq NH3 (35%,
30 mL), and extracted with CH2Cl2 (3 × 10 mL).
The combined organic phases were dried over MgSO4. Evaporation
of the solvent under reduced pressure and flash chromatography on
SiO2 (eluent: cyclohexane-EtOAc, 95:5) provided
the MOM-protected (S)-BINOL monotriflate 5
¹8 (5.90 g, 95%)
as a colorless oil. It crystallized slowly when transferred into
a refrigerator.
<A NAME="RG32508ST-20">20</A> Acetalization method:
Paleo MR.
Aurrecoechea N.
Jung K.-Y.
Rapoport H.
J.
Org. Chem.
2003,
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130
<A NAME="RG32508ST-21">21</A>
See: http://www.epa.gov/ttn/atw/hlthef/chlo-eth.html.
<A NAME="RG32508ST-22">22</A>
A suspension of benzylamine 6 (15.9 g, 38.0 mmol) and Pd (10% on
C, 2.04 g, 1.99 mmol, 5 mol%) in EtOAc (70 mL) was heated
under H2 (1 atm) at 60 ˚C for 3 h.
After filtration through Celite, the solvent was removed under reduced pressure.
The residue was dissolved in CH2Cl2 (100 mL)
and MeOH (100 mL). Concentrated H2SO4 (6.0
mL) was added and the mixture refluxed for 2 h. Saturated aq NaHCO3 (100 mL)
was added after cooling. The mixture was extracted with CH2Cl2 (3 × 50
mL). The combined organic phases were dried over MgSO4.
Evaporation of the solvent under reduced pressure provided (S)-NOBIN (1;
9.19 g, 85%) as a faintly yellow solid (pure as judged
by ¹H NMR). Recrystallization from toluene rendered
rounded white needles (8.84 g, 82%). On a smaller scale
(3.29 g of benzylamine 6) the yield of
recrystallized 1 was 1.97 g [88%;
cf. footnote (e) of Scheme
[¹]
].
<A NAME="RG32508ST-23">23</A>
Enantiopure NOBIN: 1 g ca. 500 ı [(R)- or (S)-NOBIN, ABCR],
10 g ca. 1500 $ [(R)-NOBIN],
50 g ca. 4000 $ [(S)-NOBIN,
both Shanghai FWD Chemicals].
<A NAME="RG32508ST-24">24</A>
Perillo I.
Caterina MC.
López J.
Salerno A.
Synthesis
2004,
851
<A NAME="RG32508ST-25">25</A>
Simplified Synthesis of Diamine 10²4
A
suspension of 2-bromoethylamine hydrobromide (7;
8.24 g, 40.2 mmol) and mesitylamine (9;
16.0 g, 119 mmol, 2.94 equiv) in toluene (160 mL) was refluxed for
23 h. After cooling, aq NaOH (20%, 120 mL) was added. The
mixture was extracted with EtOAc (3 × 120
mL). The combined organic phases were dried over MgSO4.
Evaporation of the solvent under reduced pressure and flash chromatography
on SiO2 (eluent: EtOAc, then EtOAc-MeOH, 1:1 + 1% Et3N) provided 10 (6.39 g, 89%) as a deep red
oil.
<A NAME="RG32508ST-26">26</A>
The following conditions were adapted
from a related transformation:¹8 Cs2CO3 (7.51
g, 23.0 mmol, 1.30 equiv) was dried in vacuo with a heat gun for
30 min. After
cooling, Pd(OAc)2 (395 mg, 1.76
mmol, 9.90 mol%),
(o-Ph2PC6H4)2O
(1.89 g, 3.51 mmol, 20 mol%), and a solution of the MOM-protected
monotriflate 5 (8.22 g, 17.8 mmol) and
the diamine 10 (4.09 g, 22.9 mmol, 1.29
equiv) in toluene (9 mL) were added. The suspension was degassed and
stirred at 115 ˚C for 14 h. Filtration through
Celite, evaporation of the solvent under reduced pressure, and flash chromatography
on SiO2 (eluent: cyclohexane-EtOAc, 90:10 → 80:20)
provided the diamine 12 (7.79 g, 89%)
as a reddish-brown sticky solid. ¹H NMR (400
MHz, CDCl3, TMS): δ = 1.91
(s, 2 × o-CH3),
2.17 (s, p-CH3), 2.95 (ddd, ³
J = ³
J = 5.5 Hz, ³
J = 2.2 Hz,
NCH2), 3.12 (s, OCH3), AB signal (δA = 3.33
ppm, δB = 3.39 ppm, J
AB = 13.0
Hz, in addition split by J
A = J
B = 5.7
Hz, NCH2), 3.85 (br s, 2 × NH),
AB signal (δA = 4.97
ppm, δB = 5.02 ppm, J
AB = 6.8
Hz, OCH2O), 6.71 (s, 2 × mesityl-H),
6.94-6.97 (m, ArH), 7.11-7.19 (mc,
2 × ArH), 7.21-7.23 (m, 2 × ArH), 7.24-7.27
(m, ArH), 7.35 (ddd, ³
J = 8.1
Hz, ³
J = 5.8
Hz, ³
J = 2.3
Hz, ArH), 7.55 (d, ³
J = 9.1
Hz, ArH), 7.76-7.78 (m, ArH), 7.86 (d, ³
J = 8.1 Hz,
ArH), 7.87 (d, ³
J = 8.9
Hz, ArH), 7.95 (d, ³
J = 9.0
Hz, ArH). HRMS (EI, 70 eV): m/z calcd
for C33H34N2O2 [M+]:
490.262028; found: 490.262202 (+0.4 ppm). [α]D
²0 -75
(c 1.05, CHCl3).