First Friedel-Crafts diacylation of a phenanthrene as the basis for an efficient synthesis of nonracemic [7]helicenes

Article abstract of DOI:10.1021/jo001055m

Reported are the first examples of Friedel-Crafts reactions used to prepare 3,6-diacylphenanthrenes. 9,10-Dimethoxyphenanthrene gives its 3,6-diacetyl derivative in good yield and in large amounts. The ketone's triisopropylsilyl enol ether when combined with 1,4-benzoquinone forms a [7]helicenebisquinone. This bisquinone's reduction product, a bishydroquinone, when combined with methanolic HCl gives the [7]helicene whose peripheral side chains are all methoxyls but whose interior hydroxyls remain. The diastereomeric (1S)-(-)-camphanates can be separated by crystallization. Their structures, analyzed by X-ray diffraction, demonstrate that the camphanates' lactone functions point away from the ring system when the helicene has the (P) configuration and toward it when the helicene has the (M) configuration. This is because the camphanates' O=C-C-O dihedral angles are, as expected, close to 0°in the former and close to 180°in the latter. Other derivatives of 3,6-diacetylphenanthrene and of [7]helicenebisquinone are prepared, and the crystal structure of one of the latter is analyzed.

Full text of DOI:10.1021/jo001055m

7602
J . Org. Chem. 2000, 65, 7602-7608
F ir st F r ied el-Cr a fts Dia cyla tion of a P h en a n th r en e a s th e Ba sis
for a n Efficien t Syn th esis of Non r a cem ic [7]Helicen es†
Kamil Paruch,‡ Thomas J . Katz,*,‡ Christopher Incarvito,§ Kin-Chung Lam,§
Brian Rhatigan,§ and Arnold L. Rheingold§
Department of Chemistry, Columbia University, New York, New York 10027, and
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
tjk1@columbia.edu
Received J uly 13, 2000
Reported are the first examples of Friedel-Crafts reactions used to prepare 3,6-diacylphenan-
threnes. 9,10-Dimethoxyphenanthrene gives its 3,6-diacetyl derivative in good yield and in large
amounts. The ketone’s triisopropylsilyl enol ether when combined with 1,4-benzoquinone forms a
[7]helicenebisquinone. This bisquinone’s reduction product, a bishydroquinone, when combined with
methanolic HCl gives the [7]helicene whose peripheral side chains are all methoxyls but whose
interior hydroxyls remain. The diastereomeric (1S)-(-)-camphanates can be separated by crystal-
lization. Their structures, analyzed by X-ray diffraction, demonstrate that the camphanates’ lactone
functions point away from the ring system when the helicene has the (P) configuration and toward
it when the helicene has the (M) configuration. This is because the camphanates’ OdC-C-O
dihedral angles are, as expected, close to 0° in the former and close to 180° in the latter. Other
derivatives of 3,6-diacetylphenanthrene and of [7]helicenebisquinone are prepared, and the crystal
structure of one of the latter is analyzed.
Sch em e 1
In tr od u ction
Since the combination of enol ethers of bis(aryl methyl
ketones) with 1,4-benzoquinone has recently made func-
tionalized helicenes available in quantity,1 and a general
procedure that resolves them into their enantiomers has
made them available in nonracemic form,1 these heli-
cenes have been used as the basis for materials that have
novel structural and optical properties,1d,2 that act as
catalysts for enantioselective transformations,3 and that
serve as chiral derivatizing agents.4 The reaction with
1,4-benzoquinone used to prepare these helicenes was
applied first to make [5]- and [6]carbohelicenes,1a,d,55 but,
remarkably, it also is effective in giving [7]carbo-
helicenes1b and a variety of heterohelicenes.1c,6
The preparation of [7]helicene 1, in abundance and
nonracemic, is outlined in Scheme 1.1b It depends on
† Dedicated to Professor J aroslav J onas of Masaryk University,
Brno, Czech Republic.
‡ Columbia University.
threediscoveries: (1) a way to make 3,6-diacetylphenan-
threnes and in large amounts; (2) the observation that,
in the reaction with 1,4-benzoquinone, silyl enol ethers
give higher yields than alkyl enol ethers;7 and (3) the
finding that the procedure previously applied to resolve
a [6]carbohelicene also succeeds for the [7].8
§ University of Delaware.
(1) (a) Katz, T. J .; Liu, L.; Willmore, N. D.; Fox, J . M.; Rheingold,
A. L.; Shi, S.; Nuckolls, C.; Rickman, B. H. J . Am. Chem. Soc. 1997,
119, 10054. (b) Fox, J . M.; Goldberg, N. R.; Katz, T. J . J . Org. Chem.
1998, 63, 7456. (c) Dreher, S. D.; Weix, D. J .; Katz, T. J . J . Org. Chem.
1999, 64, 3671. (d) Nuckolls, C.; Katz, T. J .; Katz, G.; Collings, P. J .;
Castellanos, L. J . Am. Chem. Soc. 1999, 121, 79.
(2) (a) Nuckolls, C.; Katz, T. J .; Castellanos, L. J . Am. Chem. Soc.
1996, 118, 3767. (b) Verbiest, T.; Van Elshocht, S.; Kauranen, M.;
Hellemans, L.; Snauwaert, J .; Nuckolls, C.; Katz, T. J .; Persoons, A.
Science (Washington, D.C.) 1998, 282, 913. (c) Busson, B.; Kauranen,
M.; Nuckolls, C.; Katz, T. J .; Persoons, A. Phys. Rev. Lett. 2000, 84,
79. (d) Fox, J . M.; Katz, T. J .; Van Elshocht, S.; Verbiest, T.; Kauranen,
M.; Persoons, A.; Thongpanchang, T.; Krauss, T.; Brus, L. J . Am. Chem.
Soc. 1999, 121, 3453.
(3) Dreher, S. D.; Katz, T. J .; Lam, K.-C.; Rheingold, A. L. J . Org.
Chem. 2000, 65, 815.
(4) Weix, D. J .; Dreher, S. D.; Katz, T. J . J . Am. Chem. Soc. 2000,
122, in press.
(5) Liu, L.; Katz, T. J . Tetrahedron Lett. 1990, 31, 3983.
(6) Phillips, K. E. S.; Katz, T. J .; J okusch, S.; Turro, N. J .; Lovinger,
A. J . Manuscript in preparation.
Although other approaches to [7]helicenes are being
developed, some of which9 bypass the photocyclization of
(7) The discovery was subsequently applied successfully in a number
of syntheses. See: refs 1a and 1c. Silyl enol ethers of aryl methyl
ketones had been used as dienes prior to the work in refs 1a-c, but
that they gave higher yields than other enol ethers had not been
reported. See: (a) Willmore, N. D. Ph.D. Dissertation, Columbia
University, New York, 1994. (b) Kita, Y.; Yasuda, H.; Tamura, O.;
Tamura, Y. Tetrahedron Lett. 1984, 25, 1813. (c) Kita, Y.; Okunaka,
R.; Honda, T.; Shindo, M.; Tamura, O. Tetrahedron Lett. 1989, 30, 3995.
(8) This discovery was also applied in many other syntheses. See:
Thongpanchang, T.; Paruch, K.; Katz, T. J .; Rheingold, A. L.; Lam,
K.-C.; Liable-Sands, L. J . Org. Chem. 2000, 65, 1850.
10.1021/jo001055m CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/04/2000

Friedel-Crafts Diacylation of a Phenanthrene
J . Org. Chem., Vol. 65, No. 22, 2000 7603
stilbenes,10 the procedure in Scheme 1 is the only one
reported to give a derivative of this structure on a
practical scale. Because it could therefore be useful, and
indeed it has already been used to prepare a helical
phthalocyanine,2d we considered whether and how it
might be improved and extended. The work described
below resulted in two significant improvements. One is
the discovery of an easier, cheaper, and less hazardous
way to prepare derivatives of 3,6-diacetylphenanthrene.
Two is the discovery of a way that, with the aid of the
Russig-Laatsch reaction11 and an appropriate choice of
side chains, circumvents the need for chromatography
to resolve [7]helicene enantiomers. The design of the
procedure for resolution also resulted for the first time
in the crystallization and X-ray diffraction analyses of
both diastereomers of a 1-helicenol camphanate, and
these analyses demonstrate more vividly than was previ-
ously possible the theory proposed to account for the
effectiveness of camphanates as resolving agents.8 The
crystal structures also confirm the absolute stereochem-
istries previously assigned to [7]helicenes on the basis
of their optical properties.1b The structure of a helicene-
bisquinone also has been analyzed, and it has been found
to consist (for the racemic material) of layers in which
(M)- and (P)-helicenes alternate, stacked with single
enantiomers perfectly superimposed in individual col-
umns.
The key to the synthesis is the discovery of a way to
prepare 3,6-diacetylphenanthrenes by a Friedel-Crafts
acylation. Surprisingly, there seems to be no previous
report of a phenanthrene being transformed in useful and
isolable amounts into a 3,6-disubstituted derivative,
whether by acylation or by any electrophilic substitution.
The Friedel-Crafts acetylation when applied to phenan-
threne itself gives mixtures of 2-, 3-, and 9-acetylphenan-
threnes.12 Benzoylation gives 1-benzoylphenanthrene in
up to 19% yield when the solvent is CS2, and it gives a
mixture consisting mainly of 3-benzoylphenanthrene,
along with the 1- and 2-isomers, when the solvent is
nitrobenzene.12b,13 Of other possible electrophilic substi-
tutions, the sulfonation of phenanthrene-3-sulfonic acid
gives mainly (but not exclusively) the 3,6-disulfonic
acid.14 However, the starting phenanthrene-3-sulfonic
acid can itself be obtained from the sulfonation product
Sch em e 2a
a
Reaction conditions and yields: (a) Na2S2O4, KOH or NaOH,
Bu4NBr, Me2SO4 or C12H25Br, H2O, THF (yields: 2a , 82%; 2b,
80%). (b) AcCl, AlCl3, CH2Cl2 (yields: 3a , 81%; 3b, 66%). (c)
TIPSOTf, TEA, CH2Cl2 (yield: 100%). (d) 1,4-benzoquinone, hep-
tane, reflux (yields: 5a , 23%; 5b, 20%). (e) R′I or AcCl (+DMAP),
CsF, DMF (yields: 5c, 97%; 5d , 82%; 5e, 96%). (f) AlCl3, CH2Cl2
(yield: 78%). (g) TBDMSCl, imidazole, (CH2Cl)2, reflux (yield:
75%). (h) BnBr, K2CO3, acetone, reflux (yield: 54%). (i) Ph2CCl2,
180 °C (yield: 74%).
of phenanthrene in only ca. 25% yield and then only from
a mixture including a comparable amount of the 2-sul-
fonic acid.15 The major disulfonic acid formed by 9,10-
dimethylphenanthrene is the 3,6 isomer, but it is mixed
with much more of the 3- and 2-monosulfonic acids.16
Nitration of 9,10-diacetoxyphenanthrene gives the 2,7-
dinitro derivative.17
Resu lts
As Scheme 2 summarizes, 3,6-diacetylphenanthrenes
can be prepared easily if the Friedel-Crafts acetylation
is applied to 9,10-dialkoxyphenanthrenes (in our case the
9,10-dimethoxy and 9,10-didodecyloxy derivatives), com-
pounds that themselves can be made in good yields from
9,10-phenanthrenequinone by reduction and alkylation.
These methyl ketones can then be transformed quanti-
tatively by reaction with triisopropylsilyl triflate (TIPS
triflate) into their bis(TIPS enol ethers), which with 1,4-
benzoquinone give the [7]helicenebisquinones 5a and 5b.
The TIPS substituents in these helicenes can be
replaced in one step by alkyl or acyl groups (methyl and
dodecyl were the alkyls studied, and acetyl was the acyl
studied) when the helicenes are combined with CsF and
either alkyl iodide or acyl chloride in DMF18 to which, in
the case of the acyl chloride, DMAP has been added.19
Also, the methyls of 3a ’s ethers can be replaced by other
(9) A method that uses the acetylene trimerization to give hydro
derivatives is described in the following: (a) Stara´, I. G.; Stary´, I.;
Kolla´rovicˇ, A.; Teply´, F.; Vyskocˇil, Sˇ.; Sˇaman, D. Tetrahedron Lett.
1999, 40, 1993. (b) Stara´, I. G.; Stary´, I.; Kolla´rovicˇ, A.; Teply´, F.;
Sˇaman, D.; Tichy´, M. J . Org. Chem. 1998, 63, 4046. One that cyclizes
a 3,3′-dimethyl-4,4′-biphenanthryl is described in the following: (c)
Gingras, M.; Dubois, F. Tetrahedron Lett. 1999, 40, 1309.
(10) For uses and deficits of photocylization procedures in syntheses
of [7]helicenes, see: (a) Mallory, F. B.; Mallory, C. W. Organic
Reactions; Wiley: New York, 1984; Vol. 30, p 1. (b) Laarhoven, W. H.;
Prinsen, W. J . C. Top. Curr. Chem. 1984, 125, 63. (c) Sudhakar, A.;
Katz, T. J . Tetrahedron Lett. 1986, 27, 2231. (d) Liu, L.; Yang, B.; Katz,
T. J .; Poindexter, M. K. J . Org. Chem. 1991, 56, 3769. (e) Owens, L.;
Thilgen, C.; Diederich, F.; Knobler, C. B. Helv. Chim. Acta 1993, 76,
2757. (f) Howarth, J .; Finnegan, J . Synth. Commun. 1997, 27, 3663.
(11) See: ref 3 and Dreher, S. D.; Paruch, K.; Katz, T. J . J . Org.
Chem. 2000, 65, 806 and references therein.
(12) (a) Mosettig, E.; van de Kamp, J . J . Am. Chem. Soc. 1930, 52,
3704. (b) Gore, P. H. J . Org. Chem. 1957, 22, 135. (c) Blin, P.; Bunel,
C.; Mare´chal, E. J . Chem. Res., Synop. 1978, 206. (d) Ferna´ndez, F.;
Go´mez, G.; Lo´pez, C.; Santos, A. J . Prakt. Chem. (Leipzig) 1989, 331,
15.
(13) Clar and Kelly, in a report that differs greatly from those in
ref 12, asserted that phthalic anhydride and aluminum chloride
diacylate phenanthrene in the 3 and 6 positions and that benzoyl
chloride plus AlCl3 without solvent give a pure dibenzoylphenanthrene.
See: Clar, E.; Kelly, W. J . Am. Chem. Soc. 1954, 76, 3502.
(14) Fieser, L. F. J . Am. Chem. Soc. 1929, 51, 2471.
(15) Fieser, L. F. Organic Syntheses; Wiley: New York, 1943; Collect.
Vol. II, p 482.
(16) Cerfontain, H.; Koeberg-Telder, A.; Laali, K.; Lambrechts, H.
J . A. J . Org. Chem. 1982, 47, 4069.
(17) Schmidt, J .; Schairer, O. Chem. Ber. 1923, 56, 1331.
(18) For similar replacements by alkyl groups, see ref 1b and
footnote 27 therein.
(19) Hassner, A. In Encyclopedia of Reagents for Organic Synthesis;
Paquette, L. A., Ed.; Wiley: New York, 1995; Vol. 3, p 2022.

7604 J . Org. Chem., Vol. 65, No. 22, 2000
Paruch et al.
Sch em e 3a
F igu r e 1. Structures of (M)-(-)-8 and (P)-(+)-8 according to
X-ray diffraction analyses. The OdC-C-O dihedral angles are
shown. Oxygen atoms are shown in black and carbons in white.
Hydrogens have been omitted for clarity.
a
Reaction conditions and yields: (a) Na2S2O4, Bu4NBr, EtOAc,
CH2Cl2, H2O, then HCl, MeOH, 60 °C (yield: 84%). (b) (1S)-
camphanoyl chloride, DMAP, TEA, (CH2Cl)2, reflux (yields: (P)-
8, 92%; (M)-8, 88%). (c) BuLi, THF, -78 °C, then aqueous NH4Cl
(yields:(P)-7, 96%; (M)-7, 97%).
esterified by reaction with (1S)-(-)-camphanoyl chloride.
The dextrorotatory dicamphanate crystallizes from a
mixture of toluene and cyclohexane, and the levorotatory
diastereomer can be recovered from the mother liquor.
The yields are high, 92% for the (+) isomer and 88% for
the (-).
It was possible to grow single crystals of these diaster-
eomers, allowing the structures of both to be analyzed
by X-ray diffraction. These structures, displayed in
Figure 1, identify the absolute stereochemistries of the
diastereomers, for the absolute stereochemistries of their
camphanate moieties are known to be those shown.21
They also provide striking evidence for a theory about
the conformations of camphanate groups with respect to
helicene ring systems.8 In accord with the theory, the
dihedral angles of the camphanates’ OdC-C-O groups
(labeled in half of the molecule as atoms 1, 2, 3, and 4)
are large when the helicene has the (M) configuration
(the angles are 162.2° for both its camphanates) and
small (-1.0 and -34.4°) when the helicene has the (P)
configuration.
Single crystals of racemic 5e also were grown and
analyzed by X-ray diffraction. Their structure exhibits
interesting features. It confirms the assigned connectiv-
ity, but more interestingly (Figure 2), it shows that the
individual molecules are arrayed in layers, each layer
consisting of one enantiomer, the opposite of that in the
adjacent layer. Moreover, the helix axes of molecules of
each enantiomeric configuration are perfectly superim-
posed, which means that helices twisting in the same
direction are stacked in parallel long columns. The
distance between identical molecules in one column is
11.67 Å.
One experiment that failed was to convert the enan-
tiomers of 7 into enantiomerically pure samples of 5c.
The analogous transformation works well when all of the
side chains are dodecyls,11 but when they are methyls,
oxidation with cerric ammonium nitrate gives a complex
mixture from which 5c could be isolated in only 10-21%
yield. When the oxidant was bis(trifluoroacetoxy)iodo-
benzene, the results were similar. DDQ in either pure
MeOH or a mixture of MeOH and CH2Cl2 gave only a
trace of 5c, and air in the presence of CuCl2 gave none
at all.
alkyl or silyl groups, but it requires two steps. In the first,
aluminum chloride in methylene chloride removed the
methyls,20 giving diol 3f, which in a second step was
alkylated with benzyl bromide or dichlorodiphenyl-
methane or silylated with tert-butyldimethylsilyl chloride.
These last replacements are significant because when the
benzyl or silyl groups were introduced earlier in the
synthesis, as the ethers in 2, they did not survive the
Friedel-Crafts acylation. Yet, the silyl derivative 3g is
the one1b among 3a , 3b, 3g, and 3i that gives the
[7]helicene skeleton in highest yield, and the diphenyl-
methylene derivative 3i is one whose protecting group,
after 3i is transformed into the helicene, can be removed
selectively, a property that was used in a synthesis of a
helical phthalocyanine.2d (The benzyl derivative 3h might
be used in the same way.)
To obtain nonracemic helicenes, 5c was transformed
into a mixture of tetracamphanates 6 by the action of
zinc, (1S)-(-)-camphanoyl chloride, and TMEDA in boil-
ing toluene.1b However, attempts to separate these dia-
stereomers by means of either chromatography or crys-
tallization failed. In contrast, an alternative method
(Scheme 3) that had proven to be the simplest to resolve
other helicene enantiomers3,11 was successful. That method
employs the Russig-Laatsch reaction.3,11 Thus, when 5a
is reduced with aqueous sodium dithionite and then
warmed to 60 °C with methanolic HCl, it gives 7, a
molecule with methyls attached to all of the oxygens on
the periphery, including those that had been attached
to triisopropylsilyl groups. However, there are no methyls
attached to the oxygens on the inside of the ring system.
The yield is 84%. The remaining hydroxyls can then be
(20) (a) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis;
Wiley: New York, 1967; Vol. 1, pp 30 and 31. (b) Bhatt, M. V.;
Kulkarni, S. U. Synthesis 1983, 249.
(21) Buckingham, J .; Hill, R. A. Atlas of Stereochemistry, Absolute
Configurations of Organic Molecules, 2nd ed., supplement; Chapman
and Hall: New York, 1986; p 62.

Friedel-Crafts Diacylation of a Phenanthrene
J . Org. Chem., Vol. 65, No. 22, 2000 7605
The structures determined by X-ray diffraction of (+)-
and (-)-8 (Figure 1) confirm these assignments.
The structures also provide the strongest evidence for
the theory proposed to account for why camphanates are
excellent resolving agents for helicen-1-ols.8 According to
that theory, the OdC-C-C-O dihedral angles of the
camphanate groups should, as indicated in Figure 1, be
ca. 180° when the helicene has the (M) configuration and
ca. 0° when the helicene has the (P) configuration.
Previously, this theory was supported by analyses of a
number of structurally different helicenol camphanates
of both helicities by X-ray diffraction and by ROESY
NMR supplemented by molecular mechanics calculations.
However, until now, it has not been possible to use X-ray
diffraction analyses to compare the molecular structures
of two stereoisomers, molecules that differ only in ster-
eochemistry. Figure 1 does, and by showing that the
dihedral angles are approximately those theorized, it
provides the clearest evidence for the hypothesis that the
reason (1S)-camphanates of (P)-helicen-1-ols move much
more slowly upon silica gel chromatography than the
corresponding camphanates of (M)-helicen-1-ols is that
the lactone groups in the former point away from the
helicene and in the latter point toward the helicene.
Figure 1 should also make this clear.
Also worth noting is that the diastereomers of 8
crystallize. Previously, a number of diastereomeric heli-
cene camphanates have been separated, but when the
molecules have many long aliphatic side chains, the
separations could be achieved only by means of chroma-
tography. That the diastereomers can be separated by
crystallization when the side chains are methyls was
demonstrated in two cases.3,11 The example of 8 is the
third. As expected on the basis of the conformational
analysis described, the (P) diastereomer of 8 is less
soluble than the (M) in a mixture of toluene and cyclo-
hexane, and its Rf is lower.
F igu r e 2. Structure of crystals of racemic 5e according to
X-ray diffraction analysis. The (P) enantiomers are shown
dark; the (M) enantiomers are shown light. Only three of the
molecules in each layer are displayed in these pictures. (a)
Horizontal view of five layers. (b) Vertical view of five layers,
each consisting of three molecules of the (M) enantiomer,
interleaved with five layers, each consisting of three molecules
of the (P) enantiomer. To show depth, the latter view is from
a point displaced from the perpendicular to the layers.
Discu ssion
Considering how easy it is to obtain the 3,6-diacetyl
derivatives 3a and 3b from the 9,10-dialkoxyphenan-
threnes 2a and 2b, it is surprising that previously not
only was there no clean Friedel-Crafts acylation of a
phenanthrene, but neither was there any electrophilic
substitution of 9,10-dialkoxyphenanthrene. The reason
is that almost no 9,10-dialkoxy derivatives of phenan-
threne had previously been prepared, and of those few
that had, the amounts were either small or not stated.22
Perhaps the reason for the dearth of 9,10-dialkox-
yphenanthrenes is that the procedure used here for the
alkylation, employing a two-phase system and a phase-
transfer catalyst, is critical to the success of the trans-
formation, and it was unknown in the early years of the
last century. In any case, the availability of 9,10-dialkoxy-
phenanthrenes and the discovery that 9,10-dimethoxy-
and 9,10-didodecyloxyphenanthrene can be acetylated
easily to 3,6-diacetyl derivatives suggest that 3,6-diacy-
lated 9,10-dialkoxyphenanthrenes in general will be easy
to obtain. Moreover, because they are available so simply,
it is likely that other uses will be found for them.
The only previous synthesis for such derivatives was
the one in Scheme 1, developed by Fox.1b It works well
and can be used to make significant quantities of mate-
rial. However, the Stille coupling it employs is less prac-
tical than the Friedel-Crafts reaction used here because
the reagents are more expensive, tin compounds are toxic,
and the removal of side products, mainly Bu3SnBr,
requires chromatography. For the preparation reported
here, no chromatographic purification is required.
The absolute configurations were previously assigned
to related [7]helicenes on the basis of correlations be-
tween their circular dichroism spectra and those of
helicenes, whose absolute configurations are known.1b
The observation that the diastereomers of tetracam-
phanates 6 could not be separated, while those of dicam-
phanate 8 could be easily separated, accords with the
proposition that it is only the camphanates on the insides
of the helicene structures that change conformation when
the direction in which the helicene twists changes.8
Except for one analysis in a dissertation,24 the struc-
ture displayed in Figure 2 is the first of a helicenebisqui-
none to be analyzed in detail, although two possibly
liquid-crystalline examples of nonracemic helicenebisqui-
nones have been shown by X-ray and electron diffraction
to be organized in hexagonally packed columns of closely
stacked molecules whose helix axes are superimposed.6,25
Con clu sion
9,10-Phenanthrenequinone can be sequentially re-
duced, alkylated, and acetylated, giving good yields of 3,6-
(23) (a) Rio, G.; Berthelot, J . Bull. Soc. Chim. Fr. 1972, 822. (b)
Dannenberg, H.; Keller, H.-H. Chem. Ber. 1967, 100, 23. (c) Adams,
C.; Kamkar, N. M.; Utley, J . H. P. J . Chem. Soc., Perkin Trans. 2 1979,
1767. (d) Sucharda-Sobczyk, A.; Syper, L. Rocz. Chem. 1975, 49, 749.
(e) Santamaria, J .; Ouchabane, R. Tetrahedron 1986, 42, 5559. (f)
Goldschmidt, S.; Schmidt, W. Chem. Ber. 1922, 55, 3197. (g) Fourneau,
E.; Matti, J . Bull. Soc. Chim. Fr. 1942, 633. (h) Kurebayashi, H.; Mine,
T.; Harada, K.; Usui, S.; Okajima, T.; Fukazawa, Y. Tetrahedron 1998,
54, 13495.
(24) Willmore, N. D. Ph.D. Dissertation, Columbia University, New
York, 1994. The structure Willmore describes, of racemic [5]helicene-
bisquinone, like that of racemic 5e, consists of interleaved columns of
single enantiomers.
(22) The best reported yield of 9,10-dimethoxyphenanthrene is, after
two chromatographies, 51%, and the amount prepared was 880 mg.23a
The reductant for the phenanthrenequinone was sodium in diglyme,
and dimethyl sulfate was the alkylating agent. Methyl iodide gave a
2.6% yield of noncrystalline product.23b A cathodic reduction of the
quinone, followed by methyl iodide, was said to give a 49% yield, but
no amounts or details were specified.23c Other reported syntheses of
9,10-dimethoxyphenanthrene do not state yields.23d,e The only other
reported alkylations of phenanthrene-9,10-diol are by 1-chloro-2-
diethylaminoethane, in 10% yield,23f and by 1,2-di(bromomethyl)-
benzene, in 22% yield.23g
(25) Lovinger, A. J .; Nuckolls, C.; Katz, T. J . J . Am. Chem. Soc. 1998,
120, 264.

7606 J . Org. Chem., Vol. 65, No. 22, 2000
Paruch et al.
8.6 Hz, 2H), 8.15 (d, J ) 8.6 Hz, 2H), 2.8 (s, 6H). 13C NMR
(DMSO-d6, 75 MHz): 197.9, 136.8, 132.9, 130.47, 125.6, 125.5,
123.9, 122.0, 27.1 ppm. HRMS (FAB): m/z calcd for C18H14O4,
294.0892; found, 294.0885.
diacetyl-9,10-dialkoxyphenanthrenes. These are expedi-
tiously transformed into [7]helicenebisquinones and then
into easily resolved helicenyl camphanates. X-ray dif-
fraction analyses confirm a theory explaining why cam-
phanates are excellent resolving agents.
3,6-Dia cetyl-9,10-bis(ter t-bu tyld im eth ylsiloxy)p h en a n -
th r en e (3g). A mixture of 3f (150 mg, 0.510 mmol), t-BuMe2-
SiCl (230 mg, 1.53 mmol), and imidazole (173 mg, 2.55 mmol)
in 1,2-dichloroethane (5 mL) was stirred and refluxed under
N2 by heating in an oil bath at 100 °C for 2 days. The mixture
was cooled to 25 °C, CH2Cl2 (10 mL) was added, and the
mixture was washed with 1 M HCl (2 × 30 mL). The aqueous
washings were reextracted with CH2Cl2 (5 mL), and the
combined organics were washed with saturated aqueous
NaHCO3 (30 mL) and dried over Na2SO4. Filtration, evapora-
tion of the solvent, and drying in a vacuum gave a cream-
colored solid (200 mg, 75%) whose1H and 13C NMR spectra
were identical to those published.1b
Exp er im en ta l Section
THF and heptane were distilled from Na/Ph2CO, and CH2-
Cl2 and Et3N from CaH2. DMF (anhydrous), Na2S2O4 (tech,
85%), AlCl3 (98%), AcCl (98%), 1-bromododecane (97%), and
1-iodododecane were purchased from Aldrich; phenanthrene-
quinone (95%) and CsF (99%) from Acros; and TIPSOTf (97%)
from GFS Chemicals. 1,4-Benzoquinone (98%, Aldrich) was
purified by slurrying it in CH2Cl2 with 2 times its weight of
basic alumina, filtering it through Celite, and drying it under
a vacuum. (1S)-(-)-Camphanoyl chloride was synthesized.26
The term “chromatography” refers to flash chromatography
on silica gel.27
3,6-Dia cetyl-9,10-d im eth oxyp h en a n th r en e (3a ). A mix-
ture of 9,10-phenanthrenequinone (52.0 g, 0.250 mol), Bu4NBr
(25.8 g, 0.080 mol), Na2S2O4 (130 g, 0.75 mol), THF (0.5 L),
and H2O (0.5 L) in a 4 L separatory funnel was shaken for 5
min, and then dimethyl sulfate (123 mL, 1.30 mol) was added,
followed by aqueous sodium hydroxide (128 g, 3.20 mol, in 250
mL of H2O). The mixture was shaken for 15 min, during which,
after 3 min, 300 g of ice was added to keep the mixture at
ambient temperature. The aqueous layer was separated and
extracted with EtOAc (3 × 200 mL). The combined organics
were washed with water (300 mL), 14% aqueous NH3 (2 × 200
mL), and brine (100 mL); dried over Na2SO4; and filtered.
Removal of the solvents and drying in a vacuum gave crude
9,10-dimethoxyphenanthrene (2a ) as a thick brown oil (48.7
g, 82%), which was used for the next step.
The oil, dissolved in CH2Cl2 (250 mL) plus acetyl chloride
(250 mL) in a 3 L three-necked flask fitted with an HCl trap,
was stirred and cooled by means of an ice bath. The cooling
bath was removed, and over a period of 5 min, AlCl3 (90 g,
0.67 mol) was added in portions to the stirred solution. The
mixture was then stirred for 15 min at 25 °C and then carefully
poured onto 2 L of crushed ice. The aqueous layer was
extracted with CH2Cl2 (3 × 250 mL), and the combined
organics were washed with water (250 mL) and aqueous 5%
Na2CO3 (250 mL), dried over Na2SO4, and filtered. The solvent
was evaporated, and the residual solid was dried in a vacuum
at 100 °C, shaken with MeOH (250 mL), filtered, and washed
with 150 mL of MeOH. Drying overnight in a vacuum at 100
°C afforded 52.9 g (66% based on phenanthrenequinone) of a
pale yellow solid. Mp: 161-162 °C, after recrystallization from
MeOH. IR (CCl4): 2939, 1687, 1611, 1318, 1059 cm-1. 1H NMR
(CDCl3, 400 MHz): δ 9.31 (d, J ) 1.3 Hz, 2H), 8.32 (d, J ) 8.5
Hz, 2H), 8.20 (dd, J ) 8.5, 1.3 Hz, 2H), 4.13 (s, 6H), 2.82 (s,
6H). 13C NMR (CDCl3, 75 MHz): 198.0, 145.5, 134.7, 132.6,
128.5, 126.3, 123.6, 122.8, 61.1, 27.0 ppm. UV-vis (CH3CN, c
) 1.81 × 10-4 M): λmax (log ꢀ) 266 (4.05), 325 nm (4.06). Anal.
Calcd for C20H18O4: C, 74.52; H, 5.63. Found: C, 74.52, H;
5.66.
3,6-Dia cetyl-9,10-d ih yd r oxyp h en a n th r en e (3f). A solu-
tion of 3a (6.44 g, 20.0 mmol) in CH2Cl2 (30 mL) was added
under N2 to a stirred mixture of AlCl3 (11.2 g, 0.084 mol) in
CH2Cl2 (30 mL) at 0 °C. The mixture was stirred at 0 °C for 5
min and at 25 °C for 24 h and then poured onto a slush of ice
and concentrated HCl (4:1, 500 mL). The solid was filtered,
washed on the filter with 1 M HCl (200 mL), and dissolved in
acetone (200 mL). The acetone solution was filtered and dried
(Na2SO4, 20 g), and the solvent was evaporated. The remaining
solid was suspended in CH2Cl2 (500 mL), filtered, and washed
on the filter with CH2Cl2 (100 mL). Drying in a vacuum at
100 °C gave 4.60 g (78%) of a green solid. Mp: >250 °C. IR
(KBr): 3391, 3167, 1676, 1592, 1357, 1236, 1030 cm-1. 1H NMR
(DMSO-d6, 400 MHz): δ 9.71 (s, 2H), 9.32 (s, 2H), 8.28 (d, J )
3,6-Dia cetyl-9,10-bis(ben zyloxy)p h en a n th r en e (3h ). A
solution of benzyl bromide (0.242 mL, 2.04 mmol) in acetone
(3 mL), added under N2 to a mixture of 3f (150 mg, 0.51 mmol)
and K2CO3 (282 mg, 2.04 mmol), was stirred and refluxed
under N2 for 2 days. CH2Cl2 (10 mL) was added, and the
mixture was filtered through a pad of Celite. The solvents were
evaporated, hexane (20 mL) and sand (2 g) were added to the
residue, and the mixture was shaken for 15 min. The solid
was filtered, washed with hexane (20 mL), and dissolved in
CH2Cl2 (20 mL). The solution was filtered, the solvent was
evaporated, and the residue was dried in a vacuum, boiled with
MeOH (5 mL), and, after cooling to 25 °C, filtered and washed
on the filter with MeOH (5 mL). Drying in a vacuum afforded
130 mg (54%) of 3h , a pale yellow solid. Mp: 165-167 °C. IR
(CCl4): 2927, 1688, 1610, 1431, 1357, 1316, 1046 cm-1 1H
.
NMR (CDCl3, 400 MHz): δ 9.31 (s, 2H), 8.33 (d, J ) 8.6 Hz,
2H), 8.17 (d, J ) 8.6 Hz, 2H), 7.52 (d, J ) 6.5 Hz, 4H), 7.39
(m, 6H), 5.32 (s, 4H), 2.81 (s, 6H). 13C NMR (CDCl3, 75 MHz):
197.9, 145.0, 136.8, 134.7, 132.7, 128.7, 128.4, 126.3, 123.6,
123.2, 75.6, 27.0 ppm. UV-vis (CH3CN, c ) 1.03 × 10-4 M):
λ
max (log ꢀ) 206 (4.27), 262 (4.28), 283 (sh, 4.24), 337 nm (4.17).
HRMS (FAB): m/z + H calcd for C32H26O4, 474.1829; found,
474.1851.
3,6-Dia cet yl-9,10-(d ip h en ylm et h ylen ed ioxy)p h en a n -
th r en e (3i). A mixture of 3f (100 mg, 0.34 mmol) and Ph2-
CCl2 (0.50 mL, 2.61 mmol) was stirred under N2 at 180 °C for
10 min. The resulting brown solution was cooled to 25 °C and
then mixed with hexane (10 mL). The solid was filtered,
washed on the filter with hexane (10 mL), dissolved in a
minimal amount of CH2Cl2, and loaded onto a column (1 in. ×
5 in.) of neutral alumina. Chromatography with CH2Cl2
afforded 115 mg (74%) of a pale yellow solid whose1H and 13C
NMR spectra were identical to those published.1b
9,10-Did od ecyloxyp h en a n t h r en e (2b ). A mixture of
phenanthrenequinone (10.0 g, 0.048 mol), Bu4NBr (10.0 g,
0.031 mol), and Na2S2O4 (48.0 g, 0.276 mol) in H2O (200 mL)
and THF (200 mL) was shaken for 5 min. Dodecyl bromide
(35.9 g, 0.144 mol) was added, followed by aqueous KOH (40.0
g, 0.713 mol, in 200 mL of H2O). The mixture was shaken for
2 days, poured into H2O (1.5 L), and extracted with EtOAc (2
× 200 mL and 1 × 100 mL). The extracts were washed with
H2O (2 × 1 L) and brine (100 mL), dried over Na2SO4, and
filtered. The solvent was evaporated, and the residue was
shaken for 15 min with 500 mL of 100% EtOH. The solid was
filtered and washed with EtOH (2 × 100 mL). Drying in a
vacuum afforded a pale-rose-colored solid (20.9 g, 80%), which
was used directly for the next step. An analytically pure
sample (a white solid, mp 49-50 °C) was obtained by column
chromatography (silica gel, 5:1 hexane/EtOAc). IR (CCl4):
1
2928, 2856, 1327, 1113 cm-1. H NMR (CDCl3, 400 MHz): δ
8.63 (m, 2H), 8.24 (m, 2H), 7.60 (m, 4H), 4.21 (t, J ) 6.7 Hz,
4H), 1.91 (m, 4H), 1.57 (m, 4H), 1.40-1.27 (m, 32H), 0.88 (t, J
) 6.8 Hz, 6H). 13C NMR (CDCl3, 75 MHz): 143.2, 129.6, 128.6,
126.7, 126.0, 122.6, 122.3, 73.6, 31.9, 30.5, 29.7, 29.6, 29.4, 26.3,
22.7, 14.1 ppm. UV-vis (CH2Cl2, c ) 1.05 × 10-4 M): λmax (log
ꢀ) 247 (4.27), 258 (4.21), 281 (4.01), 293 (4.04), 328 (2.97), 345
nm (3.00). Anal. Calcd for C38H58O2: C, 83.46; H, 10.69.
Found: C, 83.33; H, 10.68.
(26) Gerlach, H.; Kappes, D.; Boeckman, R. K., J r.; Maw, G. N. Org.
Synth. 1993, 71, 48.
(27) Still, W. C.; Kahn, M.; Mitra, A. J . Org. Chem. 1978, 43, 2923.

Friedel-Crafts Diacylation of a Phenanthrene
J . Org. Chem., Vol. 65, No. 22, 2000 7607
3,6-Diacetyl-9,10-didodecyloxyph en an th r en e (3b). AlCl3
(18.6 g, 140 mmol) was added in portions during 1 min to a
solution of 9,10-didodecyloxyphenanthrene (20.5 g, 37.6 mmol)
in CH2Cl2 (95 mL) and CH3COCl (130 mL) that was cooled to
5 °C. The mixture was stirred for 8 min at 25 °C and then
poured slowly onto 800 mL of crushed ice. Brine (50 mL) was
added, the organic layer was separated, and the aqueous part
was extracted with CH2Cl2 (2 × 200 mL). The combined
organics were washed with water (2 × 500 mL), saturated
aqueous NaHCO3 (100 mL), and brine (100 mL); dried over
Na2SO4; and filtered. After the solvent had been evaporated,
the residue was dried in a vacuum at 25 °C, suspended in
MeOH (300 mL), and shaken for 45 min. The solid was filtered,
washed with MeOH (150 mL), and dried on the filter. Drying
in a vacuum afforded 15.7 g (66%) of a white solid. Mp: 86-
88 °C. IR (CCl4): 2928, 1686, 1609, 1357, 1316 cm-1. 1H NMR
(CDCl3, 400 MHz): δ 9.29 (d, J ) 1.3 Hz, 2H), 8.31 (d, J ) 8.6
Hz, 2H), 8.17 (dd, J ) 8.6, 1.4 Hz, 2H), 4.24 (t, J ) 6.7 Hz,
4H), 2.80 (s, 6H), 1.92 (m, 4H), 1.57 (m, 4H), 1.41-1.27 (m, 32
H), 0.88 (t, J ) 6.8 Hz, 6 H). 13C NMR (CDCl3, 75 MHz): 197.8,
144.9, 134.5, 133.0, 128.4, 126.1, 123.5, 122.9, 73.8, 31.9, 30.4,
29.6, 29.5, 29.3, 26.9, 26.2, 22.7, 14.1 ppm. UV-vis (CH2Cl2, c
) 7.78 × 10-5 M): λmax (log ꢀ) 215 (4.20), 253 (4.40), 274 (sh,
4.29), 330 nm (4.24). Anal. Calcd for C42H62O4: C, 79.95; H,
9.91. Found: C, 79.82; H, 9.76.
6,9,10,13-Tetr am eth oxy[7]h elicen ebisqu in on e (5c). DMF
(11 mL) and MeI (1.60 mL, 25.7 mmol) were added under N2
to a mixture of 5a (0.90 g, 1.07 mmol) and CsF (0.63 g, 4.15
mmol). The mixture was stirred at 60 °C for 18 h, poured into
H2O (80 mL) plus brine (10 mL), and extracted with CH2Cl2
(5 × 10 mL). The organic part was washed with H2O (5 × 50
mL), dried over Na2SO4, and filtered. The solvent was evapo-
rated, and the residue was suspended in MeOH (20 mL),
filtered, washed on the filter with MeOH (20 mL), and dried
in a vacuum at 100 °C. The yield of a brick-red solid (mp >250
°C) was 580 mg (97%). IR (CCl4): 2939, 1662, 1607, 1462, 1384,
1
1296, 1103 cm-1. H NMR (CDCl3, 400 MHz): δ 8.46 (d, J )
8.9 Hz, 2H), 8.39 (d, J ) 8.9 Hz, 2H), 7.40 (s, 2H), 6.49 (d, J
) 10.1 Hz, 2H), 5.93 (d, J ) 10.1 Hz, 2H), 4.22 (s, 6H), 4.18 (s,
6H). 13C NMR (CDCl3, 75 MHz): 184.8, 183.5, 160.0, 145.2,
140.6, 134.0, 133.2, 129.7, 127.7, 127.4, 125.8, 125.0, 123.4,
120.5, 100.1, 61.2, 56.5 ppm. UV-vis (CH3CN, c ) 7.58 × 10-5
M): λmax (log ꢀ) 205 (4.41), 258 (4.41), 296 (4.38), 351 (4.14),
429 nm (3.69). Anal. Calcd for C34H22O8: C, 73.11; H, 3.97.
Found: C, 73.06; H, 3.95.
6,13-D ia c e t o x y -9,10-d im e t h o x y [7]h e lic e n e b is q u i-
n on e (5e). AcCl (0.339 mL, 4.75 mmol) and DMF (3.5 mL)
were added under N2 to a mixture of 5a (200 mg, 0.24 mmol),
CsF (144 mg, 0.95 mmol), and DMAP (58 mg, 0.48 mmol). The
reaction mixture was stirred vigorously for 13 h, poured into
1 M HCl (50 mL), and extracted with CH2Cl2 (1 × 10 mL and
2 × 5 mL). The combined extracts were dried over Na2SO4 and
filtered, and the solvent was evaporated. The residue was
chromatographed with 5:1 CH2Cl2/EtOAc, giving 140 mg (96%)
of an orange solid, mp >250 °C. Crystals for X-ray diffraction
analysis were grown from a solution in 2:1 PhCH3/CH2Cl2 that
was allowed to evaporate slowly at room temperature. Purple
crystals formed. IR (KBr): 2939, 1773, 1664, 1609, 1385, 1190,
1069 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.48 (d, J ) 8.9 Hz,
2H), 8.00 (d, J ) 8.9 Hz, 2H), 7.80 (s, 2H), 6.53 (d, J ) 10.2
Hz, 2H), 6.23 (d, J ) 10.2 Hz, 2H), 4.22 (s, 6H), 2.56 (s, 6H).
13C NMR (CDCl3, 75 MHz): 184.6, 183.5, 168.8, 150.8, 145.6,
140.5, 134.6, 131.9, 129.6, 129.5, 129.3, 127.5, 125.5, 124.8,
119.7, 115.2, 61.3, 21.0 ppm. UV-vis (CH3CN, c ) 5.77 × 10-5
M): λmax (log ꢀ) 251 (4.52), 285 (sh, 4.42), 327 (4.28), 425 nm
3,6-Bis(1-(tr iisop r op ylsiloxy)eth en yl)-9,10-d im eth oxy-
p h en a n th r en e (4a ). Triisopropylsilyl triflate (28.2 mL, 0.105
mol) was added under N2 to a solution of 3a (16.1 g, 0.050
mol) in CH2Cl2 (160 mL) plus Et3N (55.8 mL) that was cooled
in an ice bath. The mixture was stirred at 0 °C for 15 min and
then at 25 °C for 1 h, and after hexane (0.5 L) had been added,
it was washed with 10% aqueous KOH (1 × 300 mL and 2 ×
100 mL), dried over K2CO3, and filtered. The solvent was evap-
orated, and the oily residue was dried overnight in a vacuum
at 100 °C. The resulting slightly brown oil (32.0 g, 101%) was
used directly for the next step. IR (CCl4): 2946, 2868, 1607,
1464, 1322, 1292, 1113, 1015 cm-1 1H NMR (CDCl3, 400
.
MHz): δ 8.96 (d, J ) 1.5 Hz, 2H), 8.17 (d, J ) 8.6 Hz, 2H),
7.90 (dd, J ) 8.6, 1.6 Hz, 2H), 5.06 (d, J ) 1.8 Hz, 2H), 4.57
(d, J ) 1.8 Hz, 2H), 4.11 (s, 6H), 1.35 (m, 6H), 1.18 (d, J ) 7.3
Hz, 36H). 13C NMR (CDCl3, 75 MHz): 156.4, 144.1, 135.4,
129.1, 128.6, 124.3, 122.0, 119.5, 90.8, 61.0, 18.2, 12.8 ppm.
(sh, 3.52). Anal. Calcd for C36H22O10
Found: C, 70.31; H, 3.38.
: C, 70.36; H, 3.61.
3,6-Bis(1-(tr iisop r op ylsiloxy)eth en yl)-9,10-d id od ecyl-
oxyp h en a n th r en e (4b). Triisopropylsilyl triflate (1.99 mL,
7.40 mmol) was added to a solution of 3b (2.28 g, 3.62 mmol)
in CH2Cl2 (20 mL) and Et3N (5.0 mL) that was cooled in an
ice bath. The mixture was stirred at 0 °C for 15 min and then
at 25 °C for 1 h. Hexane (60 mL) was added, and the mixture
was washed with 10% aqueous KOH (30 mL, 2 × 10 mL), dried
over K2CO3, and filtered. The solvent was evaporated, and the
oily residue in a vacuum was dried overnight at 100 °C. The
resulting colorless oil (3.37 g, 99%) was used directly for the
next step. IR (CCl4): 2927.2, 2867, 1605, 1465, 1321, 1015
6,13-Bis(tr iisopr opylsiloxy)-9,10-dim eth oxy[7]h elicen e-
bisqu in on e (5a ). Heptane (250 mL) was added under N2 to
4a (32.0 g, 50.4 mmol) and p-benzoquinone (81 g, 0.75 mol) in
a 1 L round-bottomed flask that was fitted with a reflux
condenser. The mixture was stirred and heated in an oil bath
at 120 °C for 3 days. Then it was cooled to 25 °C, CH2Cl2 (50
mL) was added, the solid was broken into small pieces, and
the mixture was shaken for 15 min. The supernatant liquid
was decanted, and the residue was extracted with 1:1 hexane/
CH2Cl2 (6 × 200 mL). The combined solutions were filtered
through a pad of Celite, the solvents were evaporated, and the
residual benzoquinone was sublimed away in a vacuum at 100
°C. The residue was suspended in MeOH (250 mL) and shaken
until the solid became finely suspended (ca. 30 min). Water
(50 mL) was added; the mixture was shaken for 10 min; and
the solid was filtered, washed on the filter with 5:1 MeOH/
H2O, and dried in a vacuum at 100 °C. The resulting powder
was loaded onto a plug of silica gel (5 in. wide × 3 in. high),
impurities were eluted with 1:1 hexane/CH2Cl2, and the
product was eluted with 1:3 hexane/CH2Cl2. Evaporation of
the solvent and drying in a vacuum at 100 °C gave 9.47 g (23%
based on 3a ) of a dark red solid. Mp: >250 °C. IR (CCl4): 2948,
2870, 1665, 1610, 1573, 1471, 1385, 1295, 1096 cm-1. 1H NMR
(CDCl3, 400 MHz): δ 8.46 (d, J ) 8.9 Hz, 2H), 8.40 (d, J ) 8.9
Hz, 2H), 7.38 (s, 2H), 6.48 (d, J ) 10.1 Hz, 2H), 5.92 (d, J )
10.1 Hz, 2H), 4.21 (s, 6H), 1.51 (m, 6H), 1.24 (d, J ) 7.5 Hz,
18H), 1.20 (d, J ) 7.5 Hz, 18H). 13C NMR (CDCl3, 75 MHz):
184.6, 183.6, 157.4, 145.3, 140.4, 134.1, 133.0, 129.9, 129.6,
128.0, 126.1, 125.0, 123.3, 121.1, 107.7, 61.2, 18.1, 13.0 ppm.
UV-vis (CH3CN, c ) 5.50 × 10-5 M): λmax (log ꢀ) 241 (4.54),
285 (4.48), 342 (4.18), 417 nm (3.76). Anal. Calcd for C50H58O8-
Si2: C, 71.22; H, 6.93. Found: C, 70.99; H, 6.87.
1
cm-1. H NMR (CDCl3, 400 MHz): δ 8.95 (d, J ) 1.3 Hz, 2H),
8.17 (d, J ) 8.6 Hz, 2 H), 7.88 (dd, J ) 8.6, 1.3 Hz, 2H), 5.05
(d, J ) 1.7 Hz, 2H), 4.56 (d, J ) 1.7 Hz, 2H), 4.20 (t, J ) 6.7
Hz, 4H), 1.90 (m, 4H), 1.56 (m, 4H), 1.40-1.22 (m, 38 H), 1.18
(d, J ) 7.4 Hz, 36H), 0.88 (t, J ) 6.8 Hz, 6H). 13C NMR (CDCl3,
75 MHz): 156.5, 143.4, 135.2, 129.6, 128.5, 124.2, 122.1, 119.4,
90.7, 73.7, 32.0, 30.5, 29.7, 29.6, 29.4, 26.3, 22.7, 18.2, 14.1,
12.8 ppm.
6,13-Bis(t r iisop r op ylsiloxy)-9,10-d id od e cyloxy[7]-
h elicen ebisqu in on e (5b). A mixture of 4b (3.37 g, 3.58
mmol) and p-benzoquinone (5.82 g, 53.8 mmol) in heptane (50
mL) was stirred under N2 and heated at reflux in an oil bath
at 120 °C for 4 days. The mixture was cooled to 25 °C and
filtered through a pad of Celite, and the filter cake was washed
with hexane (ca. 200 mL) until the filtrate was colorless. The
solvent was evaporated, and the residue was chromato-
graphed, eluting with 1:2 CH2Cl2/hexane. The yield of a dark
red solid (mp 116-118 °C) was 0.82 g (20%). IR (CCl4): 2928,
2870, 1665, 1608, 1573, 1461, 1351, 1295, 1098 cm-1. 1H NMR
(CDCl3, 400 MHz): δ 8.46 (d, J ) 8.9 Hz, 2H), 8.38 (d, J ) 8.9
Hz, 2H), 7.38 (s, 2H), 6.47 (d, J ) 10.1 Hz, 2H), 5.92 (d, J )
10.1 Hz, 2H), 4.45 (m, 2H), 4.20 (m, 2H), 1.98 (m, 4H), 1.62-

7608 J . Org. Chem., Vol. 65, No. 22, 2000
Paruch et al.
1.20 (m, 78H), 0.89 (m, 6H). 13C NMR (CDCl3, 75 MHz): 184.7,
183.6, 157.3, 144.8, 140.4, 134.0, 132.9, 130.0, 129.8, 128.0,
126.0, 125.1, 123.5, 121.0, 107.6, 74.0, 31.9, 30.5, 29.7, 29.6,
29.4, 26.2, 22.7, 18.1, 14.1, 13.0 ppm. UV-vis (CH2Cl2, c )
5.98 × 10-5 M): λmax (log ꢀ) 246 (4.51), 288 (4.49), 345 (4.21),
425 nm (3.78). Anal. Calcd for C72H102O8Si2: C, 75.08; H, 8.93.
Found: C, 75.17; H, 8.91.
with PhCH3 (3 × 30 mL). Drying in a vacuum gave 3.50 g
(92%) of (P)-(+)-8 (a yellow solid, mp 237-239 °C). Crystals
for X-ray diffraction analysis were grown from a saturated
solution in acetone that was allowed to evaporate slowly at
room temperature. [R]D: +1646 (c ) 0.019, CH3CN). IR
(CCl4): 2938, 1798, 1774, 1602, 1284, 1236, 1110 cm-1 1H
.
NMR (CDCl3, 400 MHz): δ 8.31 (s, 4H), 7.07 (s, 2H), 6.36 (d,
J ) 8.4 Hz, 2H), 5.91 (d, J ) 8.4 Hz, 2H), 4.17 (s, 6H), 4.08 (s,
6H), 3.92 (s, 6H), 1.73 (m, 2H), 1.43 (m, 2H), 1.31 (m, 2H),
1.06 (m, 2H), 0.97 (s, 6H), 0.70 (s, 6H), 0.50 (s, 6H). 13C NMR
(CDCl3, 75 MHz): 177.5, 165.6, 153.9, 152.2, 144.2, 138.5,
128.0, 126.7, 125.0, 124.3, 123.2, 122.0, 121.0 (2 peaks), 115.7,
103.5, 97.1, 90.4, 61.2, 56.1, 55.5, 54.4, 54.1, 28.7 (2 peaks),
16.7, 16.5, 9.5 ppm. UV-vis (CH3CN, c ) 1.59 × 10-5 M): λmax
(log ꢀ) 208 (4.80), 253 (3.66), 285 (4.59), 325 (sh, 4.35), 349 nm
(sh, 3.74). CD (c ) 1.59 × 10-5 M, CH3CN), nm (∆ꢀ): 237 (178),
288 (-103), 372 (101), 399 (sh, 63).
6,9,10,13-Tetr a d od ecyloxy[7]h elicen ebisqu in on e (5d ).
DMF (20 mL) and 1-iodododecane (1.70 mL, 6.9 mmol) were
added to a mixture of 5b (0.36 g, 0.31 mmol) and CsF (0.211
g, 1.39 mmol) under N2. The mixture was stirred at 60 °C for
14 h, poured into H2O (300 mL), and extracted with CH2Cl2
(5 × 30 mL). The combined extracts were washed with H2O
(4 × 300 mL), dried over Na2SO4, and filtered. The residue
was dissolved in hexane (20 mL) and filtered through a plug
(1 in. wide × 2 in. high) of silica gel, which was washed with
hexane (100 mL) and 3:1 hexane/CH2Cl2 (50 mL). The product
was eluted with CH2Cl2 and, after removal of the solvent and
drying in a vacuum, triturated with MeOH (30 mL). The solid
was filtered, washed with MeOH (2 × 30 mL), and dried in a
vacuum. The yield of a red solid was 300 mg (82%). The 1H
and 13C NMR spectra were identical to those published.3
P r ep a r a tion of Ra cem ic 7. All operations were performed
in the absence of direct light. A solution of 5a (8.00 g, 9.50
mmol) in 3:1 EtOAc/CH2Cl2 (480 mL) was added to a solution
of Na2S2O4 (41.3 g, 237 mmol) and Bu4NBr (160 mg) in H2O
(640 mL). The mixture, in a 2 L separatory funnel, was shaken
until it became yellow (ca. 10 min) and then for 5 min more.
Brine (30 mL) was added, and the organic layer was separated,
washed with brine (2 × 150 mL), briefly dried over Na2SO4,
and filtered. The solvent was evaporated, and the resulting
yellow solid was dried in a vacuum at 25 °C. A saturated
solution of HCl gas in MeOH (40 mL) plus additional MeOH
(152 mL) were added to the solid, and the mixture, at 60 °C,
was stirred under N2 for 5 h. It was then poured into H2O (1
L) and extracted with EtOAc (300 mL). The organic part was
washed with brine (100 mL), dried over Na2SO4, and filtered.
The solvent was evaporated, and the residue, dissolved in CH2-
Cl2 (200 mL), was loaded onto a plug of silica gel (4 in. wide ×
3 in. high) that was soaked with CH2Cl2. Impurities were
eluted with CH2Cl2 (ca. 0.5 L), and then the product was eluted
with 15:1 CH2Cl2/EtOAc. The yellow fractions, which contained
the product, were collected, and the solvent was evaporated.
The solid was dried in a vacuum, suspended in pentane (2 ×
100 mL), and filtered. Drying in a vacuum at 100 °C gave 4.70
g (84%) of pure 7, a bright yellow solid. Mp: >240 °C. IR
(CCl4): 3607, 3567, 2940, 1604, 1374, 1289, 1234, 1110, 1087
The solvent was removed from the filtrate from which (P)-
(+)-8 had been separated. The residue was dissolved in 10:1
PhCH3/THF (50 mL) and loaded onto a plug of silica gel (2.5
in. wide × 4 in. high). The diastereomer with higher Rf eluted
with 10:1 PhCH3/THF. The yield of (M)-(-)-8 (a yellow solid,
mp 202-204 °C) was 3.33 g (88%). Crystals for X-ray diffrac-
tion analysis were grown by allowing a solution in 4:1 EtOAc/
MeOH to evaporate slowly at room temperature. The crystals
were yellow. [R]D: -1799 (c ) 0.018, CH3CN). IR (CCl4): 2938,
1794, 1747, 1603, 1284, 1236, 1090 cm-1. 1H NMR (CDCl3, 400
MHz): δ 8.40 (s, 4H), 7.04 (s, 2H), 6.34 (d, J ) 8.4 Hz, 2H),
5.96 (d, J ) 8.4 Hz, 2H), 4.17 (s, 6H), 4.08 (s, 6H), 3.92 (s,
6H), 1.52 (m, 2H), 1.33 (m, 4H), 0.94 (m, 2H), 0.93 (s, 6H),
0.59 (s, 6H), 0.43 ppm (s, 6H). 13C NMR (CDCl3, 75 MHz):
177.9, 165.9, 154.1, 152.2, 143.9, 138.4, 127.6, 126.8, 125.1,
123.9, 122.4, 122.1, 121.5, 120.8, 115.0, 103.1, 96.7, 89.6, 61.0,
56.0, 55.4, 54.2, 29.7, 28.5, 16.2, 16.1, 9.5 ppm. UV-vis (CH3-
CN, c ) 2.11 × 10-5 M): λmax (log ꢀ) 208 (4.77), 252 (4.63), 284
(4.62), 320 (sh, 4.39), 373 (sh, 3.83), 392 nm (sh, 3.74). CD (c
) 2.11 × 10-5 M, CH3CN), nm (∆ꢀ): 206 (62), 236 (-202), 285
(133), 320 (sh, 65), 374 (-111), 393 (sh, -80). Anal. Calcd for
C
56H54O14: C, 70.72; H, 5.72. Found: C, 70.44; H, 5.72.
(P )-(+)- a n d (M)-(-)-7. n-BuLi in hexanes (16.0 mL, 2.5
M, 40 mmol) was added slowly under N2 to a stirred solution
of (P)-(+)-8 (1.90 g, 2.00 mmol) in dry THF (50 mL) that was
cooled to -78 °C. The mixture was stirred for 20 min at -78
°C, quenched with 5 M HCl (10 mL), and then stirred for 5
min at 25 °C. The yellow solution was poured into 1 M HCl
(150 mL) and extracted with EtOAc (30 mL). The organic part
was washed with H2O (100 mL), dried over Na2SO4, and
filtered. The solvent was evaporated, and the residue was
loaded onto a short column of silica gel (1.5 in. wide and 5.5
in. high). The yellow product was eluted with 1:1 hexane/
EtOAc. Evaporation of the solvent and drying in a vacuum
gave 1.13 g (96%) of (P)-(+)-7. Mp: >240 °C. [R]D: +2563 (c )
0.018, CH3CN). The 1H and 13C NMR spectra were identical
to those of the racemic material. UV-vis (CH3CN, c ) 3.60 ×
10-5 M): λmax (log ꢀ) 249 (4.66), 301 (4.56), 362 nm (sh, 4.04).
CD (c ) 3.60 × 10-5 M, CH3CN), nm (∆ꢀ): 233 (109), 249 (sh,
42), 272 (-105), 301 (-88), 361 (78). The same procedure, when
applied to (M)-(-)-8, gave 1.14 g (97%) of (M)-(-)-7. [R]D: -2581
(c ) 0.015, CH3CN). UV-vis (CH3CN, c ) 3.98 × 10-5 M): λmax
(log ꢀ) 249 (4.68), 301 (4.58), 362 nm (sh, 4.04). CD (c ) 3.98
× 10-5 M, CH3CN), nm (∆ꢀ): 233 (-110), 249 (sh, -42), 273
(106), 301 (sh, 90), 361 (-78).
1
cm-1. H NMR (CDCl3, 400 MHz): δ 8.48 (d, J ) 8.6 Hz, 2H),
8.42 (d, J ) 8.6 Hz, 2H), 7.12 (s, 2H), 6.33 (d, J ) 8.4 Hz, 2H),
5.89 (d, J ) 8.4 Hz, 2H), 4.25 (s, 6H), 4.10 (s, 6H), 3.85 (s,
6H), 3.45 (s, 2H). 13C NMR (CDCl3, 75 MHz): 152.8, 148.0,
144.4, 143.5, 127.6, 126.1, 124.0, 123.9, 122.5, 121.3, 120.1,
117.8, 109.3, 105.2, 97.5, 61.4, 55.9, 55.7 ppm. HRMS (FAB)
m/z calcd for C36H30O8, 590.1941; found, 590.1959.
(P )-(+)- a n d (M)-(-)-8. 1,2-Dichloroethane (150 mL) and
Et3N (30 mL) were added under N2 to a mixture of 7 (4.70 g,
7.97 mmol), (1S)-(-)-camphanoyl chloride (5.18 g, 23.9 mmol),
and DMAP (1.95 g, 16.0 mmol). The mixture was stirred and
refluxed under N2 for 3 h, cooled to 25 °C, poured into 1 M
HCl (0.5 L), and extracted with EtOAc (0.5 L). The organic
layer was washed with 1 M HCl (0.5 L), 2:1 saturated aqueous
NaHCO3/brine (2 × 300 mL), and brine (100 mL); dried over
Na2SO4; and filtered. The solvent was evaporated, MeOH (50
mL) was added to the solid, and the solvent was again
evaporated. The solid residue in a vacuum was dried at 60 °C
and then mixed with MeOH (200 mL) and sand (20 g), and
the mixture was shaken for 30 min. The finely suspended
yellow solid was filtered on Celite, washed with MeOH (2 ×
100 mL), and dissolved in CH2Cl2. The solution was filtered,
and the solvent was evaporated. Drying in a vacuum at 60 °C
afforded 7.26 g of a clean mixture of the two diastereomers.
The solid was boiled in 150 mL of PhCH3 for 5 min. Cyclo-
hexane (34 mL) was added, and the mixture was cooled to 25
°C and then allowed to stand overnight in a refrigerator at 4
°C. The precipitated solid was filtered and washed on the filter
Ack n ow led gm en t. We thank the NSF for grant
support (CHE98-02316) and Dr. Alfred Bader for a
Bader Fellowship to K.P.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
and IR spectra of 2b, 3a ,b,f,h , 4a ,b, 5a -c,e, 7, (+)-8, and (-)-
8. UV spectra of 2b, 3a ,b,h , 5a -c,e, (+)-7, (-)-7, (+)-8, and
(-)-8. CD spectra of (+)-7, (-)-7, (+)-8, and (-)-8. Details of
the X-ray diffraction analyses of (P)-(+)-8, (M)-(-)-8, and 5e.
This material is available free of charge via the Internet at
http://pubs.acs.org.
J O001055M