Pearson and Carbery
JOCArticle
CDCl3) 166.0, 141.6, 136.8, 130.6, 130.2, 129.8, 127.9, 127.3, 126.4,
74.9, 47.1, 41.1, 34.5, 31.6, 26.7, 23.8, 22.2, 20.9, 16.7; HRMS (EI)
m/z calcd for C44H54O4 [Mþ] 646.4017, found 646.4018.
4.4 Hz, 0.45H), 4.77 (td, J=10.9, 4.4 Hz, 0.55H), 4.03 (s, 1.65H),
4.02 (s, 1.35H), 3.0 (s, 1.35H), 2.99 (s, 1.65H), 2.15 (dm, J =
11.9 Hz, 0.55H), 1.90-1.39 (m, 7.45H), 1.22-0.80 (m, 1H), 1.02
(d, J=6.5 Hz, 1.65H), 0.98 (d, J=7.0 Hz, 1.35H), 0.88 (d, J=
6.5 Hz, 1.35H), 0.82 (d, J = 7.0 Hz, 1.35H), 0.68 (d, J = 7.0 Hz,
1.55H), 0.57 (d, J = 7.0 Hz, 1.55H); 13C NMR (75.5 MHz,
CDCl3) 166.9, 166.6, 159.0, 158.9, 157.6, 157.5, 135.6, 135.5,
133.0, 132.8, 132.5, 132.0, 131.2, 128.9, 128.8, 128.6, 128.0,
127.7, 127.6, 127.4, 127.2, 127.1, 127.0, 126.7, 126.6, 126.4,
126.3, 125.6, 125.5, 123.7, 117.5, 99.4, 99.3, 98.9, 98.8, 74.5,
74.3, 55.4, 54.2, 54.1, 47.1, 46.8, 41.0, 40.7, 34.5, 31.6, 26.3, 23.7,
23.2, 22.3, 22.2, 21.0, 20.6, 16.5, 16.2; HRMS (EI) m/z calcd for
C35H36O4 [Mþ] 520.2608, found 520.2608.
Photocyclization Procedure. Photocyclizations were performed
on 0.10-0.20 mmol scale (c = (2-4) ꢀ 10-4 M) in a 500 mL
photoreactor. The photocyclization substrate 7a-e (1 equiv) and
iodine (2 equiv) were dissolved in 500 mL of benzene (for 7a-d) or
hexane (7e). Propylene oxide (100 equiv) was added, and the
mixture was placed in the photoreactor equipped with an immer-
sion high-pressure mercury lamp (400 W). The solution was
irradiated for 2-3 h (until total disappearance of the pink color),
and solvent was evaporated under reduced pressure. The crude red
oil was purified by column chromatography on neutral alumina.
2-(þ)-Menthyloxycarbonyl[6]helicene (8a) was obtained as a
50:50 diastereomeric mixture of M and P helicenes after chro-
matography on neutral alumina (diethyl ether/petroleum ether
2:8): c=4.10-4 M in benzene; pale yellow oil (42 mg, 42% yield);
Rf=0.40 (diethyl ether/petroleum ether 5:95); FTIR 3049, 2955,
2926, 2869, 1705, 1620, 1455, 1255; 1H NMR (300 MHz, CDCl3)
8.41 (d, J=0.8 Hz, 0.5H), 8.34 (d, J=0.8 Hz, 0.5H), 8.10-7.80
(m, 10H), 7.80 (dd, J= 8.0, 1.0 Hz, 0.5H), 7.77 (dd, J =8.0,
1.0 Hz, 0.5H), 7.57 (bd, J=8.3 Hz, 0.5H), 7.55 (bd, J=8.3 Hz,
0.5H), 7.21 (ddd, J=8.0, 7.0, 1.1 Hz, 0.5H), 7.20 (ddd, J=8.0,
7.0, 1.1 Hz, 0.5H), 6.67 (ddd, J=8.3, 7.0, 1.0 Hz, 1H), 4.73 (td,
J=10.9, 4.3 Hz, 0.5H), 4.61 (td, J=10.9, 4.3 Hz, 0.5H), 1.97-
0.77 (m, 9H), 1.06 (d, J=6.6 Hz, 1.5H), 0.99 (d, J=7.0 Hz, 1.5H),
0.87 (d, J=6.6 Hz, 1.5H), 0.72 (d, J=7.0 Hz, 1.5H), 0.71 (d, J=
7.0 Hz, 1.5H), 0.55 (d, J=7.0 Hz, 1.5H); 13C NMR (75.5 MHz,
CDCl3) 166.1, 165.9, 134.3, 134.2, 133.4, 133.3, 132.4, 132.3,
131.7, 131.6, 131.5, 131.4, 130.4, 130.2, 129.6, 129.5, 129.3,
129.2, 128.8, 128.7, 128.5, 128.4, 128.0, 127.9, 127.8, 127.7,
127.6, 127.5, 127.4, 127.3, 127.2, 127.1, 127.0, 126.9, 126.7,
126.2, 126.1, 125.8, 125.7, 125.6, 125.5, 124.8, 124.7, 124.1,
74.4, 74.3, 47.0, 46.9, 40.9, 40.7, 34.7, 34.3, 31.5, 25.9, 25.8,
23.6, 23.1, 22.5, 22.2, 21.4, 20.6, 16.5, 16.0; HRMS (ESI) m/z
calcd for C37H35O2 [M þ H] þ 511.2632, found 511.2629.
2-(-)-Menthyloxycarbonyl-14-methoxy[6]helicene (8b) was
obtained as a 50:50 diastereomeric mixture of M and P helicenes
after chromatography on neutral alumina (diethyl ether/petro-
leum ether 2:8): c=2.10-4 M in benzene; pale yellow oil (17 mg,
31% yield); Rf=0.20 (diethyl ether/petroleum ether 5:95); FTIR
3054, 2926, 2871, 1703, 1620, 1422, 1265; 1H NMR (300 MHz,
CDCl3) 8.45 (s, 0.5H), 8.38 (s, 0.5H), 8.05-7.83 (m, 10H), 7.48
(d, J=9.2 Hz, 0.5H), 7.43 (d, J=9.2 Hz, 0.5H), 7.13 (d, J=
2.8 Hz, 0.5H), 7.11 (d, J=2.8 Hz, 0.5H), 6.33 (dd, J=9.2, 2.8 Hz,
0.5H), 6.31 (dd, J=9.2, 2.8 Hz, 0.5H), 4.74 (td, J=10.6, 4.2 Hz,
0.5H), 4.60 (td, J=10.6, 4.2 Hz, 0.5H), 1.98-0.70 (m, 9H), 1.06
(d, J=6.5 Hz, 1.5H), 1.0 (d, J=7.0 Hz, 1.5H), 0.86 (d, J=6.5 Hz,
1.5H), 0.71 (d, J=7.0 Hz, 1.5H), 0.70 (d, J = 7.0 Hz, 1.5H), 0.52
(d, J=7.0 Hz, 1.5H); 13C NMR (75.5 MHz, CDCl3) 166.2, 166.0,
157.3, 134.4, 134.2, 134.0, 133.8, 133.6, 133.5, 131.5, 131.4,
130.6, 130.4, 130.3, 129.5, 129.4, 129.3, 129.1, 128.8, 128.7,
128.5, 128.4, 128.3, 128.0, 127.9, 127.8, 127.7, 127.5, 127.4,
127.3, 127.2, 127.1, 126.9, 126.8, 126.7, 125.9, 125.7, 124.5,
124.3, 123.8, 116.0, 115.9, 107.4, 107.0, 74.4, 74.3, 55.3, 55.2,
47.0, 46.8, 40.9, 40.7, 34.8, 34.4, 31.5, 31.4, 26.3, 26.0, 23.8, 23.2,
22.5, 22.2, 21.5, 20.6, 16.5, 16.1; HRMS (EI) m/z calcd for
C38H36O3 [Mþ] 540.2659, found 540.2662
2 13-Di-(-)-menthyloxycarbonyl[5]helicene (8e) was obtained
as a 70:30 mixture of M and P helicenes after chromatography on
neutral alumina (diethyl ether/petroleum ether 2:8): c=4.10-4
M
in hexane; pale yellow oil (45 mg, 35% yield); Rf = 0.40 (diethyl
ether/petroleum ether 5:95); FTIR 3050, 2948, 2927, 2864, 1710,
1450, 1264; 1H NMR (300 MHz, CDCl3) 9.27 (s, 1.4H), 9.15 (s,
0.6H), 8.16 (dd, J = 8.4, 1.4 Hz, 0.6H), 8.13 (dd, J = 8.4, 1.4 Hz,
1.4H), 8.03-7.89 (m, 8H), 4.76 (td, J = 10.6, 4.3 Hz, 0.6H), 4.71
(td, J = 10.6, 4.3 Hz, 1.4H), 2.04-1.87 (m, 2H), 1.72-1.53 (m,
4H), 1.52-1.39 (m, 6H), 1.28-1.15 (m, 2H), 1.11-0.95 (m, 2H),
0.93-0.73 (m, 2H), 0.99 (d, J =6.5Hz, 2.1H),0.84 (d, J =7.0Hz,
0.9H), 0.80 (d, J = 6.5 Hz, 0.9H), 0.66 (d, J = 7.0 Hz, 0.9H),
0.63 (d, J = 7.0 Hz, 2.1H), 0.57 (d, J = 7.0 Hz, 2.1H); 13C NMR
(75.5 MHz, CDCl3) 166.1, 135.2, 132.8, 132.6, 130.8, 130.4, 130.3,
129.9, 128.8, 128.6, 128.1, 128.0, 127.8, 127.7, 127.6, 127.5, 127.1,
127.0, 126.9, 126.5, 74.9, 74.8, 47.2, 46.8, 41.0, 40.8, 34.4, 31.1,
26.2, 25.9, 23.5, 23.1, 22.2, 22.1, 21.4, 20.7, 16.3, 15.8; HRMS (EI)
m/z calcd for C44H50O4 [Mþ] 642.3704, found 642.3707.
3-(-)-Menthyloxycarbonyl-6-[2-(3,5-difluorophenyl)ethenyl]phe-
nanthrene (12) was obtained as an unseparable 50:50 mixture of the
E and Z alkenes after chromatography on neutral alumina (diethyl
ether/petroleum ether 2:8): c=2.10-4 M in benzene; pale yellow oil
(25 mg, 41% yield); Rf=0.50 (diethyl ether/petroleum ether 5:95);
FTIR 3055, 2987, 2929, 1705, 1605, 1422, 1265; 1H NMR
(300 MHz, CDCl3) 9.47 (bs, 0.5H), 9.28 (bs, 0.5H), 8.87 (bs,
0.5H), 8.68 (bs, 0.5H), 8.23 (dd, J = 8.3, 1.5 Hz, 0.5H), 8.21 (dd,
J = 8.3, 1.5 Hz, 0.5H), 8.03 (s, 1H), 7.95-7.69 (m, 6H), 7.54 (d,
J = 16.2 Hz, 0.5H), 7.38 (m, 1H), 7.36 (d, J = 16.2 Hz, 0.5H), 7.10
(d, J = 12.2 Hz, 0.5H), 6.75 (d, J = 12.2 Hz, 0.5H), 5.08 (m, 1H),
2.22 (m, 1H), 2.04 (m, 1H), 1.81-1.75 (m, 2H), 1.63 (m, 1H), 1.29-
1.21 (m, 3H), 1.01-0.83 (m, 10H); 13C NMR (75.5 MHz, CDCl3)
166.5, 166.4, 139.5, 139.3, 135.2, 135.1, 134.9, 134.6, 133.9, 133.0,
132.7, 132.5, 132.4, 132.1, 132.0, 131.9, 131.6, 131.1, 131.0, 129.8,
129.7, 129.5, 129.1, 129.0, 128.9, 128.8, 127.8, 127.1, 126.9, 126.6,
126.5, 125.3, 125.1, 125.0, 123.8, 122.5, 121.7, 121.5, 121.1, 120.9,
75.4, 75.3, 47.6, 47.5, 41.2, 34.5, 31.7, 26.9, 24.0, 23.9, 22.7, 22.2,
20.9, 20.6, 16.8; HRMS (EI) m/z calcd for C35H32O2F6 [Mþ]
598.2301, found 598.2284.
Acknowledgment. We are grateful to EPSRC for a research
fellowship (MSMP) and the Royal Society for a research
project grant which supported this work. Prof. Alan Armstrong
and Mr. Alvaro Beneitez Martın are gratefully thanked for
´
initial support and exploratory experiments, respectively, on
this project. The EPSRC Mass Spectrometry Service, Univer-
sity of Swansea, is thanked for mass spectral analysis. We
gratefully thank Dr. Ben Greedy, Miss Hannah Maytum, and
Mr. Andrew Silvanus for assistance with attempted HPLC
separation of helicene diastereomers.
2-(þ)-Menthyloxycarbonyl-12,14-dimethoxy[5]helicene (8c)
was obtained as a 45:55 diastereomeric mixture of M and P
helicenes after chromatography on neutral alumina (diethyl
ether/petroleum ether 4:6): c = 3.5.10-4 M in benzene; pale
yellow oil (32 mg, 35% yield); Rf=0.25 (diethyl ether/petroleum
ether 1:9); FTIR 3050, 2957, 2925, 1700, 1625, 1455, 1405, 1265;
1H NMR (300 MHz, CDCl3) 9.02 (bs, 0.55H), 8.91 (bs, 0.45H),
8.11 (dd, J = 8.3, 1.6 Hz, 0.45H), 8.07 (dd, J = 8.3, 1.6 Hz,
0.55H), 8.01-7.83 (m, 7H), 7.02 (bd, J=2.4 Hz, 1H), 6.49 (d,
J=2.4 Hz, 0.55H), 6.47 (d, J=2.4 Hz, 0.45H), 4.91 (td, J = 10.9,
Supporting Information Available: General experimental
methods, characterization data, and copies of 1H and 13C NMR
spectra for all synthesized compounds. This material is available
J. Org. Chem. Vol. 74, No. 15, 2009 5325