6
S. Jones, P. Zhao / Tetrahedron: Asymmetry xxx (2013) xxx–xxx
4.31 (2H, q, J 7.2, CH2CH3 enol), 4.23–4.30 (2H, m, CH2CH3), 7.20
(1H, d, J 6.8, ArCH), 7.27–7.37 (3H, m, ArCH enol), 7.27–7.37 (1H,
m, ArCH), 7.52 (1H, td, J 7.5, 1.4, ArCH), 7.82 (1H, dd, J 7.5, 1.4, ArCH
enol), 8.07 (1H, dd, J 7.5, 0.9, ArCH), 12.51 (1H, s, COH enol); dC
(100 MHz, CDCl3) 14.2 (CH3), 14.3 (CH3, enol), 20.5 (CH2, enol),
26.4 (CH2), 27.7 (CH2), 27.8 (CH2, enol), 54.6 (CH), 60.5 (OCH2,
enol), 61.3 (OCH2), 97.0 (C@C enol), 124.3 (ArCH, enol), 126.6
(ArCH, enol), 126.9 (ArCH), 127.4 (ArCH, enol), 127.7 (ArCH),
128.7 (ArCH), 128.8 (ArCH), 130.1 (ArC, enol), 130.5 (ArCH, enol),
131.8 (ArC), 133.8 (ArCH), 139.4 (ArC, enol), 143.7 (ArC), 165.0
(C@COH, enol), 170.2 (C@O), 172.8 (C@O, enol), 193.3 (C@O); Data
were in general agreement with the literature.
(400MHz, CDCl3) 1.18 (3H, d, J 7.6, CH3), 1.73 (3H, s, CH3, enamine),
1.94 (1H, ddt, J 13.2, 4.6, 2.5, CHH), 2.10 (1H, tdd, J 13.2, 4.7, 4.1,
CHH), 2.22 (2H, t, J 7.7, CH2, enamine), 2.74 (2H, t, J 7.7, CH2, enam-
ine), 2.78 (1H, ddd, J 17.1, 4.7, 2.5, CHH), 3.11 (1H, ddd, J 17.1, 13.2,
4.6, CHH), 3.39 (1H, qdd, J 7.2, 4.1, 2.5, CH3CH), 4.03 (2H, s, PhCH2,
enamine), 4.82 (1H, d, J 16.0, PhCHH), 4.88 (1H, d, J 16.0, PhCHH),
7.16–7.47 (8H, m, ArCH, imine and enamine), 7.56 (1H, d, J 8.0,
ArCH, enamine), 8.37 (1H, d, J 8.0, ArCH); dC (100MHz, CDCl3)
15.1 (CH3), 24.4 (CH3 enamine), 24.4 (CH2), 28.5 (CH2 enamine),
28.8 (CH2), 29.5 (CH), 30.0 (CH2 enamine), 51.8 (CH2 enamine),
53.6 (NCH2), 122.6 (ArCH enamine), 126.0 (ArCH enamine), 126.3
(ArCH), 126.5 (ArCH), 126.6 (ArCH), 127.0 (ArCH enamine), 127.3
(ArCH enamine), 127.6 (ArCH), 128.0 (ArCH enamine), 128.4
(ArCH), 128.6 (ArCH), 129.8 (ArCH), 133.5 (ArC), 139.3 (ArC),
4.6. Ethyl 2-methyl-1-oxo-1,2,3,4-tetrahydronaphthalene-2-car-
boxylate 811
141.0 (ArC), 168.7 (C@N); m/z (TOF ES+) 250.1584 (MH+ C18H20
N
requires 250.1596). No analytical data are reported in the
literature.
Ethyl 1-tetralone-2-carbonate 7 (17.46 g, 80 mmol) in DMF
(40 mL) was added dropwise to a stirred suspension of NaH (60%,
4.8 g, 120 mmol) under N2 at room temperature. After 1 h, methyl
iodide (17.0 g, 7.5 mL, 120 mmol) was added, and the mixture was
left to stir for 2 h. Water (100 mL) was added carefully, and the
solution was extracted with Et2O (3 ꢁ 200 mL). The combined or-
ganic phases were washed with brine (150 mL) and dried over
MgSO4. After filtration, the filtrate was concentrated to give the
product as a yellow oil (18.5 g, 99%) that was used without further
purification. dH (400 MHz, CDCl3) 1.18 (3H, t, J 7.2, CH2CH3),
1.50 (3H, s, CH3), 2.08 (1H, ddd, J 13.7, 9.8, 5.2, CHH), 2.64
(1H, dt, J 13.7, 5.2, CHH), 2.95 (1H, dt, J 17.4, 5.2, CHH), 3.09 (1H,
ddd, J 17.4, 9.8, 5.2, CHH), 4.16 (2H, qd, J 7.2, 0.8, OCH2), 7.24
(1H, d, J 7.7, ArCH), 7.34 (1H, t, J 7.7, ArCH), 7.49 (1H, td, J 7.7,
1.1, ArCH), 8.08 (1H, dd, J 7.7, 1.1, ArCH). Data were in broad
agreement with the literature.
4.9. (1S,2S)-N-Benzyl-1-amino-2-methyl-1,2,3,4-tetrahydronaph-
thalene 119
N-[2-Methyl-3,4-dihydronaphthalen-1(2H)-ylidene]-1-phen-
ylmethanamine 10 (0.249 g, 1 mmol), catalyst
4
(0.036 g,
0.1 mmol) and dry CH2Cl2 (2 mL) were stirred under a nitrogen
atmosphere until complete dissolution. The reaction mixture was
cooled to 0 °C and HSiCl3 (0.2 mL, 2 mmol) then added by syringe
over 5–10 s. The reaction mixture was left to stir for 24 h, then CH2-
Cl2 (20 mL) and aqueous NaOH (1M, 25 mL) were added. This mix-
ture was stirred until the precipitate was completely dissolved. The
organic phases were separated and the aqueous phase was ex-
tracted with CH2Cl2 (3 ꢁ 20 mL). The combined organic phases
were washed with brine (30 mL) and dried over anhydrous MgSO4.
Filtration and concentration gave the crude product, which was
purified by chromatography on silica gel eluting with
petroleum : ethyl acetate (10:1) to afford the desired product 11
as a single diastereoisomer as a colourless oil (47% yield, ee 61%);
4.7. 2-Methyltetralone 912
Ethyl 2-methyl-1-tetralone-2-carbonate 8 (18.5 g, 80 mmol)
and aqueous HBr (48%, 135 mL) were introduced to a 250 mL
round bottom flask. The mixture was heated at reflux for 3 h,
cooled to room temperature, quenched with water (50 mL) and ex-
tracted with Et2O (3 ꢁ 100 mL). The combined organic phases were
washed with brine (100 mL) and dried over MgSO4. After filtration,
the filtrate was concentrated under reduced pressure to give an oil
that was purified by vacuum distillation (bpt. 108 °C, 3 mmHg,
lit.12 80 °C, 0.5 mmHg) to afford the desired product 9 as a colour-
less oil (9.50 g, 74%); dH (400 MHz, CDCl3) 1.29 (3H, d, J 6.8, CH3),
1.91 (1H, dddd, J 13.2, 11.9, 11.4, 4.9, CHH), 2.22 (1H, ddd, J 13.2,
8.8, 4.7, CHH), 2.61 (1H, dqd, J 11.9, 6.8, 4.7, CH3CH), 2.96–3.11
(2H, m, CH2), 7.25 (1H, d, J 7.6, ArH), 7.32 (1H, t, J 7.6, ArCH),
7.48 (1H, td, J 7.6, 1.4, ArCH), 8.06 (1H, dd, J 7.6, 1.4, ArCH); dC
(100 MHz, CDCl3) 15.5 (CH3), 28.8 (CH2), 31.4 (CH2), 42.6 (CH),
126.6 (ArCH), 127.4 (ArCH), 128.7 (ArCH), 132.4 (ArC), 133.1
(ArCH), 144.2 (ArC), 200.8 (CO). Data in broad agreement with
the literature.
½
a 2D0
ꢂ
¼ ꢀ17:0 (c 0.4, CHCl3), lit.9
½
a 2D0
ꢂ
¼ þ35:7 (c 0.9, CHCl3) for
(1R,2R) 50% ee; m
(max)/cmꢀ1 3061, 3025, 2953, 2923, 2868, 2839,
1603, 1452, 1488; dH (400 MHz, CDCl3) 1.10 (3H, d, J 6.9, CH3),
1.73–1.87 (1H, m, CHH), 1.80–1.88 (1H, m, CHH), 2.12 (1H, dqd, J
13.6, 6.9, 3.7, CH3CH), 2.78 (1H, dt, J 17.2, 7.8, CHH), 2.91 (1H, dt,
J 17.3, 5.8, CHH), 3.65 (1H, d, J 3.7, NHCH), 3.94 (2H, s, PhCH2),
7.11–7.19 (3H, m, ArCH), 7.25–7.28 (1H, m, ArCH), 7.34–7.39 (3H,
m, ArCH), 7.44 (2H, d, J 7.4, ArCH); dC (100 MHz, CDCl3) 16.3
(CH3), 26.2 (CH2), 27.6 (CH2), 32.0 (CH3CH), 52.1 (NCH2), 58.9
(NCH), 125.3 (ArCH), 126.6 (ArCH), 126.8 (ArCH), 128.2 (ArCH),
128.3 (ArCH), 128.7 (2 ꢁ ArCH), 129.1 (2 ꢁ ArCH), 136.4 (ArC),
139.7 (ArC), 141.2 (ArC); m/z (TOF ES+) 252.1744 (MH+ C18H21N re-
quires 252.1752). Enantiomeric excess was determined by compar-
ison of the integrals in the 1H NMR spectrum in CDCl3 of the
diastereomeric salts formed by an addition of excess L-mandelic
acid. Data were in broad agreement with the literature (NMR in
C6D6).
4.8. N-[2-Methyl-3,4-dihydronaphthalen-1(2H)-ylidene]-1-phen-
4.10. (E)-N-(3,4-Dihydronaphthalen-1(2H)-ylidene)-1-phenyl-
ylmethanamine 1013
methanamine 1214
Activated 4 Å molecular sieves (5.00 g), 2-methyltetralone 9
(4.80 g, 30 mmol), benzylamine (3.21 g, 30 mmol) and catalytic
amount p-toluenesulfonic acid (11.2 mg, 0.06 mmol) were dis-
solved in toluene (30 mL) and the mixture was heated at reflux
for 48 h. The mixture was cooled to room temperature, filtered
and concentrated to give an oil that was purified by vacuum distil-
lation (180 °C/0.2 mmHg) to provide the desired product 10 as a
yellow oil (2.76 g, 37%) as a 4:1 ratio of imine and enamine;
a-Tetralone (5.84 g, 40 mmol) and benzylamine (4.28 g,
40 mmol) were dissolved in toluene (36 mL) with 4 Å molecular
sieves (5.0 g) and the reaction mixture was heated at reflux over-
night. Filtration and evaporation gave a yellow oil with >95% con-
version to product from 1H NMR analysis. Purification by vacuum
distillation (180–182 °C/3 mmHg) gave the desired product as a
pale yellow oil that crystallised upon being stored in the fridge
(6.12 g, 65%). Only one geometric isomer was evident from the
NMR data; Mp: 36–38 °C; dH (400 MHz CDCl3) 2.02 (2H, quin., J
m
(max)/cmꢀ1 3062, 3026, 2926, 1684, 1629, 1598, 1494; dH