RESEARCH FRONT
Synthesis of 1,1ꢀ-Binaphthyls
571
Ph
O
O
R1
O
O
O
O
h
ϩ
2 R1
1
Acetone
R2
R2
R
R
*
*
anti-9f–k
syn-9f–k
Scheme 3.
8f–k
Table 3. Yields of compounds 9f–k
a PDDA reaction. From this point of view, the results are very
encouraging and it is to be expected that highly stereoselective
biaryl synthesis by PDDA reaction will be developed soon.
Mes, 2,4,6-trimethylphenyl
R1
R2
Yield 9 [%]
d.r. 9A
Experimental
f
tBu
Ph
4-CF3-Ph
Mes
Ph
OMe
OMe
OMe
OMe
COOMe
COOMe
86
36
75
47
28
70
50:50
43:57
58:42
38:62
52:48
57:43
g
h
i
j
k
The irradiation of esters 8 was performed in acetone at a con-
centration of ∼10−3 mol L−1 using a high-pressure mercury
arc lamp (150W, TQ150, Heraeus Nobelight GmbH, Hanau,
Germany). Light of wavelength below 300 nm was absorbed
using a Pyrex glass jacket between the lamp and the reaction
vessel. The reaction was monitored by TLC to determine when
the reactant had completely disappeared. The solution was con-
centrated under reduced pressure and the products separated by
flash chromatography (petrol ether/EtOAc 20:1) to give the pure
photoproducts 9 and/or 10. In some cases, the diastereomers of
9 were obtained as an inseparable mixture. The ratio of isomers
was acquired by irradiation of a 4 × 10−4 M solution of 8 in the
appropriate solvent for 1 h, concentration under reduced pres-
sure and determination of the ratio by 1H NMR spectroscopy of
the crude reaction mixture.
Mes
Asyn:anti ratio (syn and anti refer to the relative position of R1 and the
benzene ring marked with an asterisk in Scheme 3).
Exemplarily, the analytical data of compounds syn-9h and
anti-9h are given:
A
B
3-RS-SaRa-4-(2-methoxy-1-naphthyl)-3-(4-trifluoromethyl
phenyl)naphtho[2,3-c]furan-1(3H)-one ( syn-9h): νmax(KBr)/
cm−1 1763, 1313, 1122, 1093. δH (CDCl3, 300 MHz) 8.68
(1H, s), 8.17 (1H, d, 3J 8.5 Hz), 7.96 (1H, d, 3J 9.1 Hz),
7.66–7.56 (2H, m), 7.47–7.37 (2H, m), 7.29–7.27 (2H, m),
7.13–7.08 (1H, m), 6.80–6.72 (2H, m), 6.52–6.48 (2H, m),
6.23 (1H, s), 6.13 (1H, d, 3J 8.5 Hz), 3.86 (3H, s). δC (CDCl3,
75 MHz) 169.2, 154.5, 143.4, 136.2, 133.8, 132.7, 132.02, 131.6,
130.2, 130.0, 129.3, 129.1, 128.8, 128.4, 128.3, 127.7, 126.7,
124.3 (q, 3J 4 Hz), 124.0, 123.8, 122.6, 117.3, 112.8, 82.4,
56.6. m/z (high resolution mass spectroscopy-electron ionization
mass spectrometry) C30H19F3O3 [M]+ Calc. 484.1286. Found
484.1286.
C
Fig. 1. X-Ray structure of anti-9h.
3-SR-RaSa-4-(2-methoxy-1-naphthyl)-3-(4-trifluoromethyl
phenyl)naphtho[2,3-c]furan-1(3H)-one ( anti-9h): νmax (KBr)/
cm−1 1760, 1322, 1118, 1064. δH (CDCl3, 300 MHz) 8.69 (1H,
s), 8.17 (1H, d, 3J 8.3 Hz), 7.95–7.91 (2H, m), 7.63–7.58 (1H,
m), 7.47–7.33 (4H, m), 7.24 (2H, m), 7.09–7.05 (1H, m), 6.92
In summary, we reported on the synthesis of highly func-
tionalized 1,1ꢀ-binaphthyls 9 by PDDA cyclization of esters 8.
Whereas the influence of a bulky alkyl substituent as R1 on the
regio- and stereoselectivity of the cyclization is only marginal,
the weak attractive π-stacking interaction between two aryl
residues clearly influences the 1,1ꢀ-binaphthyl formation. The
photochemical behaviour of 8b–e demonstrates, however, that
this interaction is not strong enough to suppress the forma-
tion of the undesired phenanthrenes 10. This problem could
be circumvented by the introduction of a blocking 2-methoxy
group in the reactant 8. In the case of the resulting esters 8f–k,
a weak but clear asymmetric induction from the chiral centre to
the newly formed chirality axis was observed. Despite the mod-
erate maximum diastereomeric ratio achieved (38:62, 9i), this
is the first example of a diastereomeric synthesis of a biaryl by
3
3
(1H, d, J 9.3 Hz), 6.50 (2H, d, J 8.1 Hz), 5.98 (1H, s), 3.12
(3H, s). δC (CDCl3, 75 MHz) 170.7, 154.2, 142.2, 139.9, 136.3,
133.9, 132.7, 130.7, 130.5, 130.2, 130.0, 129.2, 128.7, 128.5,
3
127.7, 127.5, 127.2, 126.9, 124.5 (q, J 4 Hz), 123.9, 123.5,
122.6, 116.4, 111.8, 82.1, 54.9. m/z (HRMS-EI) C30H19F3O3
[M]+ Calc. 484.1286. Found 484.1286.
References
[1] (a) K. C. Nicolaou, H. Li, C. N. C. Boddy, J. M. Ramanjulu, T.-Y.Yue,
S. Natarajan, X.-J. Chu, S. Bräse, F. Rübsam, Chem. Eur. J. 1999,