Is the CD excitron chirality method applicable to chiral 1,1'- biphenanthryl compounds? [9]

Full text of DOI:10.1021/ja981797l

9086
J. Am. Chem. Soc. 1998, 120, 9086-9087
Is the CD Exciton Chirality Method Applicable to
Chiral 1,1′-Biphenanthryl Compounds?
Tetsutaro Hattori,* Kenta Sakurai, Nobuyuki Koike, and
Sotaro Miyano*
Department of Biomolecular Engineering
Graduate School of Engineering, Tohoku UniVersity
Aramaki-Aoba 07, Aoba-ku
Sendai 980-8579, Japan
Hitoshi Goto, Fuyuka Ishiya, and Nobuyuki Harada*
Institute for Chemical Reaction Science
Tohoku UniVersity, 2-1-1 Katahira, Aoba
Sendai 980-8577, Japan
ReceiVed May 26, 1998
In the last two decades, many axially chiral 1,1′-binaphthyl
derivatives have been successfully used as highly efficient chiral
auxiliaries for chiral molecular recognition as well as asymmetric
syntheses. In some cases, enhanced chiral recognition abilities
have been brought by 4,4′- or 9,9′-biphenanthryl analogues by
virtue of the more expanded aromatic plane.1 To our knowledge,
however, 1,1′-biphenanthryl compounds have never been utilized
as chirality-recognizing auxiliaries, although members of this class
of biaryl derivatives have often been isolated as natural products.2
On the other hand, the CD exciton chirality method has been
established as a nonempirical method for determining absolute
stereochemistry of chiral organic compounds.3 We report here
the synthesis and absolute stereochemistry of chiral 1,1′-biphenan-
thryl compounds and also discuss their anomalous CD behavior
which disagrees with the prediction by the CD exciton chirality
method. It was disclosed that the apparent discrepancy was due
to an extra hidden transition, and simple qualitative predictions
by the CD exciton chirality method are not valid for the
phenanthrene chromophores.
Figure 1. CD and UV spectra of (aR)-1,1′-biphenanthryl derivatives in
EtOH or in 10% v/v 1,4-dioxane/EtOH. In (aR)-(+)-5, two long axes of
phenanthrene chromophores constitute a counterclockwise screw sense.
1,1′-biphenanthryl-2,2′-diyl thiophosphoramide (2) (70%).7 The
mixture was crystallized from ethanol/ethyl acetate (4:1), and
crystals (aS,S)-(+)-2a obtained were washed with refluxing
acetonitrile to remove the remaining more soluble diastereomer
2b. Reduction of amide 2a with LiAlH4 in THF gave enantiopure
(-)-1 (72%), the enantiopurity of which was confirmed by HPLC
on a Pirkle column [(R)-N-(3,5-dinitrobenzoyl)phenylglycine-
modified column] with hexane/2-propanol (7:3).6,8
The absolute configuration of 1 was determined by the axial
chirality recognition method developed by us, which is based on
the steric requirement for the formation of a 12-membered cyclic
diester, e.g., compound 4.9 Treatment of (()-1 with 1.0 mol equiv
of 1,1′-binaphthalene-2,2′-dicarbonyl dichloride (aR)-3 in reflux-
ing benzene/pyridine (60:1) in the presence of 4-(dimethylamino)-
pyridine (DMAP, 2.0 mol equiv) allowed cyclization of only
(aR)-1 to yield diastereomerically pure cyclic diester 4, which
should have (aR,aR) configuration because of less steric hindrance
(Supporting Information). Reductive cleavage of diester (aR,aR)-4
with LiAlH4 recovered (+)-1, the enantiomeric homogeneity of
which was confirmed by chiral HPLC analyses. The aR absolute
stereochemistry was thus assigned to (+)-1.
Prerequisite 2-phenanthrol was easily obtained by alkali fusion
of barium phenanthrene-2-sulfonate which was prepared according
to Fieser’s procedure.4 Oxidative coupling of 2-phenanthrol in
the presence of 1-phenylethylamine-copper (II) complex afforded
1,1′-biphenanthryl-2,2′-diol (1) (72%).5,6 Enantioresolution of
We were very surprised to observe the unexpected shape of
the CD spectra of (+)-1 and its dimethyl ether (+)-5 (Figure 1
and Supporting Information);10 we had expected that the CD
spectra of (aR)-1 and (aR)-5 should show exciton split Cotton
(()-1 was achieved as follows: treatment of (()-1 with thio-
phosphoryl chloride and (S)-1-phenylethylamine in refluxing
pyridine gave a diastereomeric mixture of N-[(S)-1-phenylethyl]-
1
effects3 of negative chirality in the Bb transition region around
(1) Hayashi, T.; Iwamura, H.; Naito, M.; Matsumoto, Y.; Uozumi, Y. J.
Am. Chem. Soc. 1994, 116, 775. Lee, G.-H.; Wang, Y.; Tanaka, K.; Toda, F.
Chem. Lett. 1988, 781 and references therein.
(2) Adam, K. P.; Becker, H. Phytochemistry 1994, 35, 139 and references
therein.
(3) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy: Exciton
Coupling in Organic Stereochemistry; University Science Books: Mill Valley,
CA, and Oxford University Press: Oxford, 1983.
(4) Fieser, L. F. Organic Syntheses; Wiley & Sons: New York, 1945;
Collect. Vol. II, 482.
1
260 nm. Since the Bb transition of phenanthrene is polarized
along the long axis of the chromophore (perpendicular to the
(7) Fabbri, D.; Delogu, G.; Lucchi, O. D. J. Org. Chem. 1993, 58, 1748.
(8) Pirkle, W. H.; House, D. W.; Finn, J. M. J. Chromatogr. 1980, 192,
143.
(9) Koike, N.; Hattori, T.; Miyano, S. Tetrahedron: Asymmetry 1994, 5,
1899 and references therein.
(10) (aR)-(+)-1: UV (10% v/v 1,4-dioxane/EtOH) λmax 258.6 nm (ꢀ 101,
000); CD (10% v/v 1,4-dioxane/EtOH) λext 273.8 nm (∆ꢀ +48.7), 258.2
(-80.8). (aR)-(+)-5: UV (10% v/v 1,4-dioxane/EtOH) λmax 260.6 nm (ꢀ 83,
100); CD (10% v/v 1,4-dioxane/EtOH) λext 274.2 nm (∆ꢀ +38.5), 258.0
(-52.5).
(5) Feringa, B.; Wynberg, H. Tetrahedron Lett. 1977, 50, 4447.
(6) (()-1, mp 297-299 °C (EtOAc); (aS)-(-)-1, mp 244-245 °C (EtOAc),
[R]22 -34.0 (c 0.95, CHCl3); (aR)-(+)-1, mp 243-244 °C (EtOAc), [R]19
D
+32.D0 (c 1.60, CHCl3).
S0002-7863(98)01797-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/20/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 35, 1998 9087
Scheme 1a
a (a) Br2, CH2Cl2, 78 °C f room temp, 5 h, 80%. (b) NaH, CH3I,
DMF, 0 °C f room temp, 4 h. (c) 9-MeO2CC3H6-BBN, Pd(PPh3)4,
NaOH, THF, 65 °C, 24 h, 95%. (d) NaOH, aqueous EtOH, reflux, 1.5 h,
88%. (e) PCl5, PhH, room temp, 2 h, and then SnCl4, 5 °C, 1.5 h, 81%.
(f) LiAlH4, THF, room temp, 1 h, and then TsOH, acetone, reflux, 5.5 h,
92%. (g) H2, Pd/C, EtOH, room temp, 21 h, 79%. (h) DDQ, PhMe, 80
°C, 20 h, 73%. (i) BBr3, CH2Cl2, room temp, 2 h, 92%.
Figure 2. CD and UV spectral curves of (aR)-1,1′-biphenanthryl 12
calculated by the π-electron SCF-CI-DV MO method.
biphenanthryl compounds disagree with the prediction by the CD
exciton chirality method. To clarify the mechanism of such
strange CD behavior of 1,1′-biphenanthryls and also to determine
their absolute stereochemistry by the theoretical CD method, we
carried out the theoretical calculation of CD and UV spectra of
(aR)-1,1′-biphenanthryl 12 and (aR)-5 by the π-electron SCF-CI-
DV MO method.3 The calculation of UV spectrum of phenan-
threne revealed that there is another electric transition with short-
axis polarization around 255 nm in addition to the main band of
1Bb transition around 260 nm. It was also clarified that in the
system of (aR)-12, these two transitions in each chromophore
interact with one another (i.e., four sets of interactions) giving
rise to positive first and negative second Cotton effects, which
are opposite in sign to those expected from the qualitative
application of the CD exciton chirality method. It should be
emphasized that the CD exciton chirality method itself is correct,
but the electronic transitions of phenanthrene are complex. For
this reason, simple qualitative predictions based on the exciton
method are not valid for 1,1′-biphenanthryl compounds.
The CD and UV spectra of (aR)-12 quantitatively calculated
by the π-electron SCF-CI-DV MO method are shown in Figure
2; the calculated CD and UV curves are in a good agreement
with the observed spectra, although there is a weak negative CD
band around 290 nm (see also Supporting Information). The
absolute stereochemistries of 1,1′-biphenanthryl-2,2′-diol (+)-1
and its dimethyl ether (+)-5 were thus theoretically determined
to be aR in consistency with the chemical correlation results
described above. Further studies for other biphenanthryl deriva-
tives are now in progress.
symmetry axis of C2V phenanthrene),11 two long axes of phenan-
threne chromophores constitute a counterclockwise screw sense,
i.e., negative exciton chirality, as illustrated in Figure 1. Both
compounds (aR)-(+)-1 and (aR)-(+)-5, however, exhibit positive
and negative CD Cotton effects around 274 and 260 nm,
respectively, although their ∆ꢀ values are relatively small.10 This
unexpected and strange CD behavior prompted us to reinvestigate
the absolute stereochemistry of 1,1′-biphenanthryl derivatives.
The absolute stereochemistry of (+)-1 and its derivatives was
unambiguously determined by chemical correlation to 1,1′-
binaphthyl-2,2′-diol (aR)-(+)-6 (Scheme 1). Bromination of
enantiopure (aR)-(+)-6, followed by methylation gave bis(bromo
ether) (aR)-(-)-7, which was subjected to the Suzuki coupling
reaction with 9-[(3-methoxycarbonyl)propyl]-9-borabicyclo[3.3.1]-
nonane and then alkaline hydrolysis yielding dicarboxylic acid
(aR)-(-)-8. The Friedel-Crafts cyclization of (aR)-(-)-8 af-
forded diketone (aR)-(+)-9,12 which was reduced with LiAlH4
and then dehydrated with p-toluenesulfonic acid to give tetrahy-
drobiphenanthryl (aR)-(-)-11. Hydrogenation of (aR)-(-)-11
gave octahydrobiphenanthryl (aR)-(+)-10. Hydrocarbon (aR)-
(-)-11 was dehydrogenated with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ) affording dimethyl ether (aR)-(+)-5, which
was converted to (aR)-(+)-1 by demethylation with boron
tribromide: total yield, 27% based on the starting binaphthol 6.
The aR absolute stereochemistry of (+)-1 was thus established.
The CD spectrum of octahydrobiphenanthryl (aR)-(+)-10
shows typical and intense exciton split CD Cotton effects of
negative chirality reflecting the counterclockwise screw sense
between two long axes of naphthalene chromophores (Figure 1).13
Tetrahydrobiphenanthryl (aR)-(-)-11 also exhibits bisignate Cot-
ton effects of negative exciton chirality. On the other hand, the
CD spectra of 1,1′-biphenanthryl compounds (aR)-(+)-1 and (aR)-
(+)-5 show positive first and negative second Cotton effects
(Figure 1 and Supporting Information).10 These CD data of 1,1′-
Acknowledgment. This work was supported in part by grants from
the Ministry of Education, Science, Sports, and Culture, Japan (Scientific
Research (A) No. 08405058 and (B) No. 10555318 to S.M., Scientific
Research (A) No. 07408032, (B) No. 10554035, Priority Areas No.
10146205, and International Joint No. 10045022 to N.H.) and the Ciba-
Geigy Foundation (Japan) for the Promotion of Science (to N.H.).
(11) Yamamura, K.; Ono, S.; Ogoshi, H.; Masuda, H.; Kuroda, Y. Synlett.
1989, 18. Harada, N.; Hattori, T.; Suzuki, T.; Okamura, A.; Ono, H.; Miyano,
S.; Uda, H. Tetrahedron: Asymmetry 1993, 4, 1789.
(12) Bachmann, W. E.; Cortes, G. D. J. Am. Chem. Soc. 1943, 65, 1329.
(13) (aR)-(+)-10: UV (EtOH) λmax 233.8 nm (ꢀ 116 000); CD (EtOH) λext
239.8 nm (∆ꢀ -197.1), 227.8 (+133.3). (aR)-(-)-11: UV (EtOH) λmax 245.8
nm (ꢀ 74 900); CD (EtOH) λext 249.6 nm (∆ꢀ -112.6), 236.4 (+60.5).
Supporting Information Available: Spectral and physical data of
compounds 1-11, CD and UV spectra of (aR)-(+)-1, and calculated CD
and UV curves of (aR)-5 (4 pages, print/PDF). See any current masthead
page for ordering information and Web access instructions.
JA981797L