Light-Powered Chiral Molecular Motor, Part 1
897, 857, 811, 747, 659, 643, 620, 560, 512, 481 cm–1. C14H14O2 (d, J = 14.6 Hz, 2 H, 3eq-H), 3.59 (dd, J = 14.6, 6.8 Hz, 2 H, 3ax-
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(214.26): calcd. C 78.48, H 6.59; found C 78.55, H 6.68.
H), 3.64 (dq, J = 6.8, 6.8 Hz, 2 H, 2eq-H), 6.35 (ddd, J = 8.3, 6.8,
1.2 Hz, 2 H, 8-H), 6.60 (dd, J = 8.3, 1.2 Hz, 2 H, 9-H), 6.96 (ddd,
J = 8.0, 6.8, 1.2 Hz, 2 H, 7-H), 7.51 (d, J = 8.0 Hz, 2 H, 4-H), 7.65
(d, J = 8.0 Hz, 2 H, 6-H), 7.71 (d, J = 8.0 Hz, 2 H, 5-H) ppm; for
2-Methyl-2,3-dihydro-1H-benz[e]inden-1-one (8): A mixture of pro-
pionic acid 7 (0.423 g, 1.98 mmol) and PCl5 (0.535 g, 2.57 mmol)
in toluene (10 mL) was stirred at room temperature for 1 h, and
SnCl4 (0.46 mL, 3.95 mmol) was then added at 0°C. After having
been stirred at room temperature for 13 h, the reaction mixture was
treated at 0°C with HCl (2 , 5 mL) and extracted three times with
toluene. The combined organic layers were washed with aqueous
NaHCO3, water, and brine and dried over anhydrous MgSO4, and
the solvents were evaporated to dryness. The crude product was
purified by short column chromatography on silica gel (hexane/
EtOAc, 5:1), yielding ketone 8 as a colorless oil (0.380 g, 98%). 1H
other NMR spectroscopic data, see Table 2. IR (KBr): νmax = 3049,
˜
2958, 2924, 2863, 2842, 1621, 1585, 1515, 1452, 1434, 1367, 1304,
1212, 1163, 1054, 1025, 955, 906, 863, 809, 783, 741, 687, 658, 614,
579, 533, 515 cm–1. HRMS: calcd. for C28H24 m/z 360.1878; found
360.1862. C28H24 (360.50): calcd. C 93.29, H 6.71; found C 93.50,
H 6.93.
Preparation of trans- and cis-2-Methyl-2,3-dihydro-1H-benz[e]inden-
1-ols: LiAlH4 (0.011 g, 0.28 mmol) was added at 0°C to a solution
NMR (600 MHz, CDCl3): δ = 1.38 (d, J = 7.3 Hz, 3 H), 2.79–2.85 of ketone ( )-8 (0.055 g, 0.28 mmol) in dry THF (5 mL), and the
(m, 2 H), 3.48 (dd, J = 17.9, 8.0 Hz, 1 H), 7.50 (d, J = 8.2 Hz, 1
H), 7.55 (ddd, J = 8.1, 6.9, 1.0 Hz, 1 H), 7.67 (ddd, J = 8.2, 6.9,
reaction mixture was stirred at room temperature for 1 h. The mix-
ture was treated with a small amount of aqueous NH4Cl, and the
1.3 Hz, 1 H), 7.88 (d, J = 8.1 Hz, 1 H), 8.04 (d, J = 8.2 Hz, 1 H), organic layer was dried over anhydrous MgSO4 and evaporated un-
9.15 (dd, J = 8.2, 1.0 Hz, 1 H) ppm. 13C NMR (150 MHz, CDCl3):
δ = 16.6, 35.4, 42.4, 123.9, 124.0, 126.5, 128.1, 128.8, 129.6, 130.2,
der reduced pressure. The residue was subjected to short column
chromatography on silica gel, and the obtained epimeric alcohols
were separated by HPLC on silica gel (hexane/EtOAc, 10:1), yield-
ing ( )-cis-9 (0.026 g, 47 %) as the alcohol eluted first and ( )-
trans-10 (0.029 g, 51%) as the alcohol eluted second.
132.7, 135.7, 156.6, 210.0 ppm. IR (neat): νmax = 3055, 2963, 2929,
˜
2871, 1694, 1628, 1593, 1573, 1517, 1456, 1439, 1372, 1312, 1202,
1171, 1152, 1116, 1073, 1024, 920, 881, 821, 789, 747, 631, 564,
512, 494 cm–1. C14H12O (196.25): calcd. C 85.68, H 6.16; found C
85.51, H 6.31.
( )-cis-2-Methyl-2,3-dihydro-1H-benz[e]inden-1-ol (9): Colorless
prisms with m.p. 121°C. 1H NMR (600 MHz, CDCl3): δ = 1.31 (d,
Synthesis of the Racemic Molecular Motors (2S*,2ЈS*)-(M*,M*)- J = 7.1 Hz, 3 H), 1.49 (br.s, 1 H), 2.64 (dddq, J = 8.7, 7.7, 6.1,
(E)-( )-2,2Ј-Dimethyl-2,2Ј,3,3Ј-tetrahydro-1,1Ј-bi[1H-benz[e]indeny-
lidene] (2a) and (2S*,2ЈS*)-(M*,M*)-(Z)-( )-2,2Ј-Dimethyl-
2,2Ј,3,3Ј-tetrahydro-1,1Ј-bi[1H-benz[e]indenylidene] (2c): A mixture
of LiAlH4 (0.0944 g, 2.49 mmol) and dry THF (10 mL) was added
dropwise to a suspension of TiCl3 (0.768 g, 4.98 mmol) in dry THF
(20 mL), cooled to 0°C. The mixture was stirred at 0°C for 0.5 h
and was then heated gently at reflux for 1.5 h. After a solution of
ketone 8 (0.326 g, 1.66 mmol) in dry THF (20 mL) had been added,
the reaction mixture was heated gently at reflux for 96 h. The reac-
tion mixture was filtered with Celite, and the filtrate was treated
with dilute aqueous HCl and extracted three times with CHCl3.
The combined organic layers were washed with brine and dried
over anhydrous MgSO4, and the solvents were evaporated to dry-
ness. The crude product was purified by short column chromatog-
raphy on silica gel (hexane/AcOEt, 20:1), by HPLC (silica gel, hex-
ane), and finally by HPLC (ODS, MeOH). The ( )-cis-olefin
(2S*,2ЈS*)-(M*,M*)-(Z)-( )-2c was obtained as faint yellow need-
les (0.0167 g, 6%) from the first fraction eluted, whilst the trans-
olefin (2S*,2ЈS*)-(M*,M*)-(E)-( )-2a was obtained as colorless
prisms (0.0407 mg, 14%) from the second fraction eluted.
7.0 Hz, 1 H), 2.86 (dd, J = 15.8, 8.7 Hz, 1 H), 3.09 (dd, J = 15.8,
7.7 Hz, 1 H), 5.49 (d, J = 6.1 Hz, 1 H), 7.37 (d, J = 8.4 Hz, 1 H),
7.44 (ddd, J = 8.2, 6.9, 1.1 Hz, 1 H), 7.53 (ddd, J = 8.3, 6.9, 1.3 Hz,
1 H), 7.77 (d, J = 8.4 Hz, 1 H), 7.85 (d, J = 8.2 Hz, 1 H), 8.08 (dd,
J = 8.3, 1.1 Hz, 1 H) ppm. 13C NMR (150 MHz, CDCl3): δ =
13.89, 39.12, 39.32, 76.27, 123.33, 123.81, 125.03, 126.59, 128.49,
129.27, 130.24, 132.93, 139.72, 141.80 ppm. IR (KBr): νmax = 3204,
˜
3050, 2966, 2935, 2909, 2876, 2844, 1593, 1513, 1438, 1377, 1317,
1241, 1169, 1135, 918, 807, 747, 672 cm–1. C14H14O (198.26): calcd.
C 84.81, H 7.12; found C 84.84, H 7.25.
( )-trans-2-Methyl-2,3-dihydro-1H-benz[e]inden-1-ol (10): Colorless
needles with m.p. 86–87°C. 1H NMR (600 MHz, CDCl3): δ = 1.25
(d, J = 7.0 Hz, 3 H), 1.62 (br.s, 1 H), 2.51 (dddq, J = 7.7, 4.9, 3.8,
7.0 Hz, 1 H), 2.59 (dd, J = 16.0, 4.9 Hz, 1 H), 3.43 (dd, J = 16.0,
7.7 Hz, 1 H), 5.29 (d, J = 3.8 Hz, 1 H), 7.36 (d, J = 8.2 Hz, 1 H),
7.45 (ddd, J = 8.1, 6.9, 1.1 Hz, 1 H), 7.53 (ddd, J = 8.3, 6.9, 1.3 Hz,
1 H), 7.78 (d, J = 8.2 Hz, 1 H), 7.86 (br.dd, J = 8.3, 1.1 Hz, 1 H),
8.22 (br. dd, J = 8.1, 1.3 Hz, 1 H) ppm. 13C NMR (150 MHz,
CDCl3): δ = 19.09, 38.95, 43.99, 83.09, 123.55, 123.87, 125.09,
126.47, 128.52, 129.38, 130.53, 133.08, 138.34, 140.64 ppm. IR
(2S*,2ЈS*)-(M*,M*)-(E)-( )-2,2Ј-Dimethyl-2,2Ј,3,3Ј-tetrahydro-
(KBr): νmax = 3245, 3050, 2958, 2928, 2902, 2850, 1592, 1514, 1453,
˜
1,1Ј-bi[1H-benz[e]indenylidene] (2a): m.p. 191–192 °C. 1H NMR 1375, 1260, 1159, 1073, 1010, 812, 745, 661 cm–1. C14H14
O
(400 MHz, CD2Cl2): δ = 1.29 (d, J = 6.4 Hz, 6 H, 2ax-Me), 2.35
(d, J = 14.6 Hz, 1 H, 3eq-H), 2.95 (dd, J = 14.6, 5.6 Hz, 2 H, 3ax-
H), 3.03 (dq, J = 6.4, 5.6 Hz, 2 H, 2eq-H), 7.41 (d, J = 8.3 Hz, 2
H, 4-H), 7.47 (ddd, J = 8.1, 6.8, 1.2 Hz, 2 H, 7-H), 7.55 (ddd, J =
8.3, 6.8, 1.4 Hz, 2 H, 8-H), 7.76 (d, J = 8.3 Hz, 2 H, 5-H), 7.90 (d,
J = 8.1 Hz, 2 H, 6-H), 8.24 (d, J = 8.3 Hz, 2 H, 9-H) ppm; for
(198.26): calcd. C 84.81, H 7.12; found C 84.91, H 7.20.
Enantioresolution of Alcohol ( )-cis-9 by the CSDP Acid Method:
A mixture of alcohol ( )-cis-9 (0.022 g, 0.11 mmol), CSDP acid
(1S,2R,4R)-(–)-3 (0.107 g, 0.25 mmol), DCC (0.051 g, 0.25 mmol),
and DMAP (0.003 g, 0.03 mmol) in CH2Cl2 (1 mL) was stirred at
room temperature overnight. After addition of a small amount of
water, the mixture was stirred for 1 h, diluted with EtOAc, and
filtered with Celite, which was washed with EtOAc. The organic
layer was evaporated under reduced pressure, and the residue was
subjected to short column chromatography on silica gel (hexane/
EtOAc, 10:1). The diastereomeric esters obtained were separated
by HPLC on silica gel (25×300 mm column, hexane/EtOAc, 10:1;
separation factor α = 1.17; resolution factor Rs = 1.79), giving
other NMR spectroscopic data, see Table 1. IR (KBr): νmax = 3048,
˜
2968, 2926, 2868, 2840, 1559, 1542, 1515, 1456, 1435, 1364, 1300,
1252, 1215, 1154, 1020, 966, 868, 845, 810, 782, 754, 711, 665, 598,
555, 526 cm–1. High-resolution mass spectrum (HRMS): calcd. for
C28H24 m/z 360.1878; found 360.1881. C28H24 (360.50): calcd. C
93.29, H 6.71; found C 93.16, H 6.74.
(2S*,2ЈS*)-(M*,M*)-(Z)-( )-2,2Ј-Dimethyl-2,2Ј,3,3Ј-tetrahydro-
1,1Ј-bi[1H-benz[e]indenylidene] (2c): m.p. 174–175 °C. 1H NMR (1R,2R)-(–)-cis-11a (0.034 g, 50 %) as the ester eluted first and
(400 MHz, CD2Cl2): δ = 1.21 (d, J = 6.8 Hz, 6 H, 2ax-Me), 2.70
(1S,2S)-(–)-cis-11b (0.033 g, 49%) as the one eluted second.
Eur. J. Org. Chem. 2005, 4533–4543
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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