Easy Synthesis of Functionalized Hetero[7]helicenes

Article abstract of DOI:10.1021/jo990065o

Hetero[7]helicenebisquinones can be synthesized easily on a multigram scale by combining the silyl enol ethers of 3,6-diacetyldibenzofuran, 3,6-diacetyldibenzothiophene, and 3,6-diacetylcarbazole with p-benzoquinone. They can be resolved into their enantiomers by a procedure that had previously been used to resolve carbohelicenebisquinones. Their absolute configurations are assigned.

Full text of DOI:10.1021/jo990065o

J . Org. Chem. 1999, 64, 3671-3678
3671
Ea sy Syn th esis of F u n ction a lized Heter o[7]h elicen es
Spencer D. Dreher, Daniel J . Weix, and Thomas J . Katz*
Department of Chemistry, Columbia University, New York, New York, 10027
Received J anuary 13, 1999
Hetero[7]helicenebisquinones can be synthesized easily on a multigram scale by combining the
silyl enol ethers of 3,6-diacetyldibenzofuran, 3,6-diacetyldibenzothiophene, and 3,6-diacetylcarbazole
with p-benzoquinone. They can be resolved into their enantiomers by a procedure that had previously
been used to resolve carbohelicenebisquinones. Their absolute configurations are assigned.
Sch em e 1
In tr od u ction
By applying steps such as those illustrated in Scheme
1 to a variety of diacetylaromatic hydrocarbons, it had
been possible to synthesize [5]-,1 [6]-,1 and [7]-carbohe-
licenes2 in much larger amounts than before and with
useful functional groups. Because Friedel-Crafts acety-
lation, followed in the case of the nitrogen compounds
by N-alkylation, transforms dibenzofuran, dibenzothio-
phene, and carbazole into their 3,6-diacetyl derivatives
2a -d ,3 the possibility was considered that procedures
similar to Scheme 1 would convert these heterocyclic
diacetyl compounds into hetero[7]helicenes (Scheme 2).
Because it is easier to prepare these diacetyls than those
used for the previous syntheses based on Scheme 1,1,2
these steps would lead easily to functionalized helicenes.
They would also be significant because only three heli-
cenes (and an OH-derivative of one of them4) were known
in which some of the benzene rings are replaced by
furans,5 and only two (and some methyl derivatives) were
known in which they are replaced by pyrroles.6 Of these
oxa- and azahelicenes, only one, an azahelicene, had been
obtained optically active (but in only a minuscule
amount).6d A number of helicenes are known in which
some of the benzene rings are replaced by thiophenes,
but their syntheses require more steps.7 Moreover, he-
licenes synthesized according to Scheme 2 should benefit
from the quinone functions, which in the case of carbocy-
clic analogues were useful for resolving the enantio-
mers,1,2,8 for transforming the molecules into nonracemic
fully conjugated polymers,9 and for promoting the mol-
Sch em e 2
ecules’ self-association into columnar aggregates and
liquid crystals8,10 that exhibit exceptional rotatory8,10 and
nonlinear optical properties.11
We show below that the heterocyclic helicenes 4a -d
can be prepared easily in gram quantities, that they can
(1) 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.
(2) Fox, J . M.; Goldberg, N. R.; Katz, T. J . J . Org. Chem. 1998, 63,
7456.
(3) For 3,6-diacetyldibenzofuran, see: (a) Bruce, M. J .; McLean, G.
A.; Royles, B. L. J .; Smith, D. M.; Standring, P. N. J . Chem. Soc., Perkin
Trans. 1 1995, 1789 and a reference cited therein. For 3,6-diacetyl-
carbazole, see: (b) Buu-Ho¨ı, N. P.; Royer, R. Recl. Trav. Chim. Pays-
Bas 1947, 66, 533. (c) Plant, S. G. P.; Rogers, K. M.; Williams, S. B. C.
J . Chem. Soc. 1935, 741. For 3,6-diacetyldibenzothiophene, see: (a)
above and (d) Albrecht, W. L.; Gustafson, D. H.; Horgan, S. W. J . Org.
Chem. 1972, 37, 3355. (e) Gilman, H.; Nobis, J . F. J . Am. Chem. Soc.
1949, 71, 274. (f) Burger, A.; Wartman, W. B., J r.; Lutz, R. E. J . Am.
Chem. Soc. 1938, 60, 2628.
(4) Erdtman, H.; Ho¨gberg, H.-E. Tetrahedron 1979, 35, 535.
(5) (a) Chatterjea, J . N.; Banerji, K. D. J . Indian Chem. Soc. 1970,
47, 576. (b) Ho¨gberg, H.-E. Acta Chem. Scand. 1973, 27, 2591. (c)
Groen, M. B.; Schadenberg, H.; Wynberg, H. J . Org. Chem. 1971, 36,
2797.
(7) (a) Lehman, P. G.; Wynberg, H. Aust. J . Chem. 1974, 27, 315
and references therein. (b) Tanaka, K.; Osuga, H.; Suzuki, H.; Shogase,
Y.; Kitahara, Y. J . Chem. Soc., Perkin Trans. 1 1998, 935 and
references therein. (c) Osuga, H.; Suzuki, H.; Tanaka, K. Bull. Chem.
Soc. J pn. 1997, 70, 891 and references therein. (d) Tanaka, K.; Kume,
T.; Takimoto, T.; Kitahara, Y.; Suzuki, H.; Osuga, H.; Kawai, Y. Chem.
Lett. 1997, 501. (e) Tanaka, K.; Suzuki, H.; Osuga, H. J . Org. Chem.
1997, 62, 4465 and references therein. (f) Tanaka, K.; Osuga, H.;
Koyama, K.; Suzuki, H.; Imai, K.; Yoshida, Y. Enantiomer 1997, 2,
193. (g) Tanaka, K.; Osuga, H.; Shogase, Y.; Suzuki, H. Tetrahedron
Lett. 1995, 36, 915. (h) Larsen, J .; Bechgaard, K. Acta Chem. Scand.
1996, 50, 71. (i) Dore, A.; Fabbri, D.; Gladiali, S.; Valle, G. Tetrahe-
dron: Asymmetry 1995, 6, 779. (j) Larsen, J .; Bechgaard, K. Acta Chem.
Scand. 1996, 50, 77. (k) Larsen, J .; Bechgaard, K. J . Org. Chem. 1996,
61, 1151.
(6) (a) Fuchs, W.; Niszel, F. Chem. Ber. 1927, 60, 209. (b) Zander,
M.; Franke, W. H. Chem. Ber. 1969, 102, 2728. (c) Teuber, H.-J .; Vogel,
L. Chem. Ber. 1970, 103, 3319. (d) Pischel, I.; Grimme, S.; Kotila, S.;
Nieger, M.; Vo¨gtle, F. Tetrahedron: Asymmetry 1996, 7, 109.
(8) (a) Nuckolls, C.; Katz, T. J .; Castellanos, L. J . Am. Chem. Soc.
1996, 118, 3767. (b) Nuckolls, C.; Katz, T. J .; Katz, G.; Collings, P. J .;
Castellanos, L. J . Am. Chem. Soc. 1999, 121, 79.
(9) Dai, Y.; Katz, T. J . J . Org. Chem. 1997, 62, 1274.
10.1021/jo990065o CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/29/1999

3672 J . Org. Chem., Vol. 64, No. 10, 1999
Dreher et al.
Ta ble 1. Yield s of 4 a n d 5 Wh en 3 Wa s Com bin ed w ith
Sch em e 3
p-Ben zoqu in on e in Tolu en e
enol
ether 3
reaction
temp (°C)
reaction
time (h)
yield of
4 (%)
yield of
5 (%)
a
b
c
d
100
105
90
48
24
11
14
40
33
53
50
22
19
23
a
85
a
Not isolated.
be resolved into their enantiomers by procedures identi-
cal to those used previously to resolve carbohelicenes, and
that the enantiomers do not racemize at an appreciable
rate at room temperature.
structures, 6a -d , which would be expected to have two
doublet and three singlet aromatic resonances, were
detected. Helicenes 4a -d are all easily separable from
their isomers, 5a -d , and in the case of 4d , the separation
could be accomplished simply by triturating the mixture
with pentanes. The isomer is soluble; the helicene is
not! Accordingly, this helicene is easily and cheaply
preparable on a large scale. To separate the other
helicenes (4a -c) from their isomers required silica gel
chromatography, which, although not difficult, is more
expensive.
Side-products analogous to 5 are not observed in
Scheme 1, the corresponding preparation of the carbocy-
clic product 1. The regioselectivity of this reaction is
presumed to reflect the greater reactivity of R-positions
compared to â-positions in naphthalenes, which, as
indicated in Scheme 3 (here X ) CHdCH), can be
attributed to the loss of the second ring’s aromatic
structure when additions are to â- rather than to R-posi-
tions. Accordingly, we speculate that the lower regiose-
lectivity in Scheme 2 is a consequence of an energy
difference between the two modes of reaction in Scheme
3 that is smaller when X ) O, N, and S than when X )
CHdCH.13 Because there are no analogous Diels-Alder
reactions of appropriate vinylbenzofurans, -thiophenes,
or -pyrroles as precedents, we used the Spartan AM1
computer program14 to model simplified transition-state
structures 7 and 8. We then compared the energies of
Resu lts a n d Discu ssion
The four diacetylheteroaromatics in Scheme 2 (2a -d ),
with triisopropylsilyl triflate (TIPSOTf) and triethyl-
amine in methylene chloride, gave the bis(triisopropyl-
silylenol ethers) 3a -d in 91-99% yields, and these
combined with p-benzoquinone in toluene as summarized
in Table 1. Helicenes 4a -d were obtained in acceptable
yields. More significantly, because the starting enol
ethers are so easy to prepare from inexpensive dibenzo-
furan, dibenzothiophene, and carbazole, the amounts that
could be made (in our preparations, between 3.1 and 16.0
g) are large when compared to the amounts of heterohe-
licenes preparable by other procedures. In the reactions
with p-benzoquinone, the helicenes 4a -d form very much
faster than the carbohelicenes previously prepared in
similar ways, which means (for the best case) that the
transformation of carbazole into enantiomerically pure
helicene 9d (see below) takes less than 3 days to
complete.
Helicenes 4a-d are accompanied by significant amounts
of the isomeric products with structures 5a -d (see Table
1). Structures 5a -d were assigned on the basis of the
the two structures in the heterocyclic and carbocyclic
systems. In accord with the hypothesis, the calculated
differences between 7a and 8a (4.6 kcal/mol), 7b and 8b
(8.6 kcal/mol), and 7c and 8c (8.6 kcal/mol) are signifi-
cantly lower than between 7d and 8d (17.4 kcal/mol).
Analogy between these Diels-Alder reactions and stil-
bene photocyclizations also provides support: electronic
effects similar to those considered for the two modes of
reaction in Scheme 3 have been invoked to explain the
regioselectivities of the photoprocesses.15 Moreover, in the
absence of significant steric hindrance, the regioselec-
1H NMR spectra, each of which displays aromatic proton
resonances comprised of six doublets and four singlets.
Moreover, in each case, one of the singlets is at δ ca. 10
ppm, indicative of the lone proton in the bay region of
the ring system.12 None of the third possible isomeric
(10) (a) Nuckolls, C.; Katz, T. J . J . Am. Chem. Soc. 1998, 120, 9541.
(b) Nuckolls, C.; Katz, T. J .; Verbiest, T.; Van Elshocht, S.; Kuball,
H.-G.; Kiesewalter, S.; Lovinger, A. J .; Persoons, A. J . Am. Chem. Soc.
1998, 120, 8656.
(11) (a) 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. (b) 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.
(12) (a) Brison, J .; de Bakker, C.; Defay, N.; Geerts-Evard, F.;
Marchant, M.-J .; Martin R. H. Bull. Soc. Chim. Belg. 1983, 92, 901.
(b) Katz, T. J .; Sudhakar, A.; Teasley, M. F.; Gilbert, A. M.; Geiger,
W. E.; Robben, M. P.; Wuensch, M.; Ward, M. D. J . Am. Chem. Soc.
1993, 115, 3182.
(13) The aromatic stabilization of benzene is greater than that of
furan, thiophene, and pyrrole (Bird, C. W.; Cheeseman, G. W. H. In
Comprehensive Heterocylic Chemistry; Katritzky, A. R., Rees, C. W.,
Eds.; Pergamon: Oxford, 1984; Vol. 4, pp 28-32). Accordingly, deriva-
tives of the latter three should lose less upon reaction by pathway â.
(14) Dewar, M. J . S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J . J . P.
J . Am. Chem. Soc. 1985, 107, 3902.

Synthesis of Functionalized Hetero[7]helicenes
J . Org. Chem., Vol. 64, No. 10, 1999 3673
Sch em e 4
Sch em e 5
F igu r e 1. CD spectra of 2.4 × 10-5 M solutions of (P)-(+)-
10a (‚‚‚), (P)-(+)-10b (- - -), and (P)-(+)-10c (s) in CH3CN.
spectra for the isomers of 10a -c that are dextrorotatory
at 589 nm (the wavelength of the sodium D line), and
the Supporting Information includes the spectra of their
diastereomers. The latter are essentially mirror images
of the former. The CD spectrum of (+)-10b between 250
and 350 nm and near 400 nm is similar to the CD spectra
of the dextrorotatory enantiomers of three thiohelicenes
known to have (P)-, or right-handed, helicity: the parent
of 10b, in which the BuO and Z groups are replaced by
Hs;18 11;19 and 12.7e Accordingly, it is likely that (+)-10b
also has (P)-helicity. Moreover, the similarity of the three
CD spectra in Figure 1 implies that all three molecules
have the same helicity. Because the CD spectra of (+)-
and (-)-10d are almost identical to those of (+)- and (-)-
10c, their dextrorotatory isomers, too, undoubtedly have
the same helicity. Accordingly, (+)-10a , (+)-10c, and (+)-
10d are all assigned (P)-configurations. For (+)-10c and
(+)-10d , this assignment agrees with the similarity
between their CD spectra and that of (+)-13, which is
believed to have (P)-helicity because its CD spectrum
matches one calculated.6d,20
a
Reagents and conditions: (a) CsF, n-BuI, DMF, 60 °C (86-
99% yields); (b) (S)-(-)-camphanoyl chloride, Zn, (Me2NCH2)2,
PhMe, reflux (75-92% yields); (c) MeLi or BuLi, then chloranil
(63-88% yields).
tivity of photocyclization, like that of the Diels-Alder
reactions considered above, seems to be lower when X )
S than when X ) CHdCH, at least for the example
illustrated in Scheme 4.16,17
Presumably steric effects can divert the bonds from
forming at the electronically favored R-position. Thus,
that Scheme 2 gives 4 and 5 but not 6 suggests that the
electronic effects that direct the cycloadditions to R in
Scheme 3 cause the first of the Diels-Alders to convert
the ring system into a derivative of [5]helicene, but when
X ) O, N, and S, these effects are partially overcome in
the second Diels-Alder reaction by steric repulsions.
However, when X ) CHdCH, the electronic effect is more
powerful; it is not overcome by similar or greater steric
hindrance. Accordingly, Scheme 1 gives 1 uncontami-
nated by significant amounts of the analogue of 5.
Resolu tion of th e En a n tiom er s of th e Heter oh e-
licen ebisqu in on es. As shown in Scheme 5, cesium
fluoride removed the triisopropylsilyl groups, and alkyl
iodide replaced them with alkyls. Reduction by zinc and
esterification with (S)-(-)-camphanoyl chloride gave
camphanate esters 10a -d , each of which was separated
into its diastereomers by silica gel chromatography. In
each case, the diastereomeric excess was greater than
97%.
That the helicities are unchanged when camphanates
10 are stored and transformed at room temperature into
helicenebisquinones 9 is shown by experiments in which
samples of 9a -c in DMF were heated at 78 °C for 24 h.
The circular dichroisms of 9b and 9c decreased by
5-13%, and that of 9a decreased by 45%. Moreover, the
specific rotations of the (+)- and (-)-9b (prepared,
The absolute configurations of the camphanate esters
are implied by their CD spectra. Figure 1 shows these
(15) Mallory, F. B.; Mallory C. W. Organic Reactions; Wiley: New
York, 1984; Vol. 30, p 48ff.
(18) Gottarelli, G.; Proni, G.; Spada, G. P.; Fabbri, D.; Gladiali, S.;
Rosini, C. J . Org. Chem. 1996, 61, 2013.
(19) (a) Groen, M. B.; Wynberg, H. J . Am. Chem. Soc. 1971, 93, 2968.
(b) Groen, M. B.; Stulen, G.; Visser, G. J .; Wynberg, H. J . Am. Chem.
Soc. 1970, 92, 7218. (c) Tribout, J .; Martin, R. H.; Doyle, M.; Wynberg,
H. Tetrahedron Lett. 1972, 2839. (d) Nakazaki, M.; Yamamoto, K.;
Maeda, M. J . Org. Chem. 1981, 46, 1985.
(16) The dashed line in Scheme 4 indicates that photoirradiation
cyclizes the carbocyclic [5]helicene further, to benzo[g,h,i]perylene.17b
(17) For X ) S, see: (a) Tedjamulia, M. L.; Tominaga, Y.; Castle, R.
N.; Lee, M. L. J . Heterocycl. Chem. 1983, 20, 861. For X ) CHdCH,
see: (b) Dietz, F.; Scholz, M. Tetrahedron 1968, 24, 6845. (c) Le Guen,
M. M. J .; Shafig, Y. E.-D.; Taylor, R. J . Chem. Soc., Perkin Trans. 2
1979, 803.
(20) Grimme, S.; Harren, J .; Sobanski, A.; Vo¨gtle, F. Eur. J . Org.
Chem. 1998, 1491.

3674 J . Org. Chem., Vol. 64, No. 10, 1999
Dreher et al.
prior to use. Zn dust (Aldrich, <10 µm, 98%) was activated
prior to use.21 (S)-(-)-Camphanic acid was prepared on a 100
g scale.22 1,4-Benzoquinone (Aldrich, 98%) was purified by
slurrying it in CH2Cl2 with 4 times its weight of basic alumina,
filtering through Celite, and drying under vacuum. Glassware
was flame-dried under vacuum and cooled under N2. Reactions
were run under N2. Additions by syringe were through rubber
septa. Chromatography refers to flash chromatography. What-
man 60 Å silica plates were used for TLC analyses.
P r ep a r a tion of Dia cetyl Com p ou n d s. Dibenzofuran with
acetyl chloride and AlCl3 in 1,2-dichloroethane gave 2a 3a (mp
161-162; lit.23 161-162 °C). 1H NMR (CDCl3, 400 MHz): δ
8.64 (d, 2H, 1.8 Hz), 8.16 (dd, 2H, 1.8 and 6.8 Hz), 7.64 (d, 2H,
8.7 Hz), 2.74 ppm (s, 6H).24 13C NMR (CDCl3, 75 MHz): δ
196.9, 159.5, 133.1, 128.7, 124.1, 121.9, 112.0, 26.8 ppm.
Dibenzothiophene similarly gave 2b3a (mp 204-205 °C; lit.3d
204-205.5 °C). 1H NMR (CDCl3, 400 MHz): δ 8.81 (d, 2H, 1.6
Hz), 8.09 (dd, 2H, 1.6 and 6.8 Hz), 7.93 (d, 2H, 8.4 Hz), 2.76
ppm (s, 6H).3d 13C NMR (CDCl3, 75 MHz): δ 197.4, 144.7,
135.3, 134.2, 126.9, 122.9, 122.0, 26.8 ppm, similar to that
reported.25
Carbazole with acetyl chloride and AlCl3 in CS2 gave 3,6-
diacetylcarbazole3b (mp 232-233 °C; lit.3b 232 °C). 1H NMR
(DMSO-d6, referenced to the DMSO peak, 400 MHz): δ 12.06
(s, 1H), 9.00 (d, 2H, 1.6 Hz), 8.05 (dd, 2H, 1.6 and 6.9 Hz),
7.59 (d, 2H, 8.6 Hz), 2.68 ppm (s, 6H). 13C NMR (DMSO-d6,
referenced to the DMSO peak, 75 MHz): δ 197.1, 143.3, 129.2,
126.4, 122.7, 122.5, 111.3, 26.7 ppm. With dimethyl sulfate
and KOH in acetone3c the latter gave 2c (mp 195-196 °C, lit.3c
1
F igu r e 2. CD spectra (top, ordinate on the left) and UV-vis
absorption spectra (bottom, ordinate on the right) of 5.4 × 10-5
M solutions of (P)-9a (‚‚‚), (P)-(+)-9b (- - -), and (P)-9c (s) in
CH3CN.
195 °C). H NMR (CDCl3, 400 MHz): δ 8.73 (d, 2H, 1.3 Hz),
8.16 (dd, 2H, 1.7 and 5.9 Hz), 7.41 (d, 2H, 8.6 Hz), 3.88 (s,
3H), 2.73 ppm (s, 6H). 13C NMR (CDCl3, 75 MHz): δ 197.4,
144.3, 129.8, 127.0, 122.8, 121.8, 108.7, 29.5, 26.6 ppm.
3,6-Diacetylcarbazole (10.0 g, 40 mmol) was refluxed for 1
h with 1-iodododecane (35.4 g, 119 mmol, 30.0 mL), KOH-
saturated H2O (50 mL), and acetone (200 mL). After it had
cooled to room temperature, the reaction mixture was diluted
with Et2O, washed twice with H2O, and dried (Na2SO4). The
solvent was removed. The addition of hexanes (ca. 250 mL)
precipitated a white solid, which when filtered, washed with
cold hexanes, and dried, amounted to 15.8 g (95%) of pure 2d ,
respectively, from the (+)- and (-)-diastereomers of 10b)
are identical except for their signs: +1350 and -1300.
Thus, the CD spectra of 9a -d derived from dextrorota-
tory 10a -d (Figure 2 and Supporting Information) are
those of the (P)-enantiomers. In accord with the assign-
ment, the CD peaks between ca. 350 and 400 nm and at
ca. 253 nm are positive, and the one at ca. 279 nm
negative, as in the spectra of (+)-(P)-1 (TIPS replaced
by C12H25, and R ) C12H25 or R,R ) Ph2C).2 We note
incidentally that the specific rotations of 9a , 9c, and 9d
at the D wavelength could not be measured because the
compounds absorb too strongly at 589 nm (Figure 2).
mp 97-99 °C. IR (CCl4) 1680 cm-1 1H NMR (CDCl3, 400
.
MHz): δ 8.80 (d, 2H, 1.6 Hz), 8.18 (dd, 2H, 1.7 and 7.0 Hz),
7.46 (d, 2H, 8.7 Hz), 4.35 (t, 2H, 7.2 Hz), 2.75 (s, 6H), 1.89 (m,
2H), 1.34 (m, 2H), 1.22 (m, 18H), 0.87 ppm (t, 3H, 6.7 Hz). 13
C
NMR (CDCl3, 75 MHz): δ 197.4, 143.9, 129.7, 127.0, 122.8,
122.0, 109.0, 43.6, 31.9, 29.5, 29.3 (m), 28.9, 27.2, 26.7, 22.6,
14.1 ppm. Anal. Calcd for C28H37NO2: C, 80.13; H, 8.90; N,
3.34. Found: C, 79.94; H, 9.06; N, 3.22.
Gen er al P r ocedu r e A. P r epar ation of Silyl En ol Eth er s.
3,6-Bis[1-(t r iisop r op ylsiloxy)-et h en yl]-N-m et h ylca r b a -
zole (3c). Triisopropylsilyl triflate (12.1 g, 39.6 mmol, 10.6
mL) was added to a solution, cooled in an ice bath, of 2c (5.0
g, 18.9 mmol) and Et3N (15.7 mL) in CH2Cl2 (95 mL), and the
mixture was warmed to room temperature and then stirred
for 2 h. The reaction mixture was diluted with CH2Cl2, washed
three times with saturated NaHCO3, and dried (Na2SO4). The
solvent was evaporated. The pink solid was dissolved in a
minimal amount of CH2Cl2, and MeOH was added until a
precipitate formed. The CH2Cl2 was evaporated, and the solid
in the remaining MeOH was filtered, washed with MeOH, and
heated at 100 °C for 2 h in a vacuum, giving 10.2 g (94%) of a
white solid (3c, mp 166-170 °C). 1H NMR (acetone-d6,
referenced to the acetone peak, 300 MHz): δ 8.46 (d, 2H, 1.4
Hz), 7.83 (m, 2H), 7.49 (m, 2H), 4.98 (d, 2H, 1.7 Hz), 4.45 (d,
Con clu sion s
Grams of hetero[7]helicenes 4a -d can be synthesized
in only three or four steps from cheap materials. Fur-
thermore, helicene 4d can be obtained pure without the
need for chromatography. The enantiomers can be re-
solved by the same procedure previously used to resolve
those of carbohelicenes, and their absolute configurations
could be assigned. 9a and 10a are the first nonracemic
oxahelicenes to have been made.
Exp er im en ta l Section
THF was distilled from Na/benzophenone; toluene was
distilled from Na; and CH2Cl2, ClCH2CH2Cl, and Et3N were
distilled from CaH2. Dibenzofuran (97%, Aldrich), AlCl3 (99%,
Aldrich), acetyl chloride (98%, Aldrich), dibenzothiophene
(98%, Aldrich), carbazole (96%, Acros), CS2 (anhydrous, 99+%,
Aldrich), dimethyl sulfate (99+%, Aldrich), triisopropylsilyl
triflate (GFS, 98%), 1-iodobutane (99%, Aldrich), 1-iododode-
cane (99%, Acros), CsF (99%, Aldrich), N,N,N′,N′-tetrameth-
ylethylenediamine (TMEDA, Aldrich, anhydrous, 99.5%), MeLi
(1.6 M in Et2O, Acros), n-BuLi (2.6M in hexanes, Acros), and
chloranil (99%, Aldrich) were used without purification. DMF
(Aldrich, anhydrous, 99.8%) was boiled and cooled under N2
(21) Shriner R. L.; Neumann, F. Organic Syntheses; Wiley: New
York, 1955; Collect. Vol. III, p 73.
(22) Gerlach, H.; Kappes, D.; Boeckmann, R. K.; Maw, G. N. Organic
Syntheses; Wiley: New York, 1993; Vol. 71, p 48.
(23) Helgeson, R. C.; Lauer, M.; Cram, D. J . J . Chem Soc., Chem.
Commun. 1983, 101.
(24) Our 1H NMR spectra of 2a and 2b do not match those in ref
3a. However, the spectrum of 2b does match that in ref 3d.
(25) Filimonov, V. D.; Filippova, T. A.; Lopatinskii, V. P.; Sukhoroslo-
va, M. M. Chem. Heterocycl. Compd. 1984, 20, 165.

Synthesis of Functionalized Hetero[7]helicenes
J . Org. Chem., Vol. 64, No. 10, 1999 3675
2H, 1.7 Hz), 3.91 (s, 3H), 1.36 (m, 6H), 1.19 ppm (m, 38H). 13
NMR (acetone-d6, referenced to the acetone peak, 75 MHz): δ
157.3, 142.0, 129.6, 124.1, 122.9, 117.2, 109.0, 88.5, 18.1, 13.2
ppm.
C
1H), 7.02 (d, 1H, 10.1 Hz), 6.88 (d, 2H, 10.1 Hz), 6.84 (d, 1H,
10.1 Hz), 6.78 (d, 1H, 10.1 Hz), 4.05 (s, 3H), 1.46 (m, 7H), 1.15
ppm (m, 39H). 13C NMR (CDCl3, 75 MHz): δ 187.8, 187.1,
187.0, 183.8, 159.5, 159.3, 146.5, 143.6, 141.7, 141.6, 135.8,
135.6, 135.3, 134.3, 130.3, 128.0, 126.6 (two peaks), 125.1,
124.6, 123.1, 120.2, 116.6, 113.1, 107.2, 106.0, 105.4, 30.2, 18.7,
18.5, 13.6, 13.5 ppm. UV-vis (CH2Cl2, c ) 3.7 × 10-5 M), λmax
(log ꢀ): 580 (3.58), 450 (3.94), 365 (sh, 4.10), 345 (4.20), 290
(4.30), 240 nm (4.30).
3,6-Bis-[1-(tr iisopr opylsiloxy)eth en yl]diben zofu r an (3a).
Procedure A. Triisopropylsilyl triflate (10.1 g, 33 mmol, 8.9
mL), CH2Cl2 (80 mL), Et3N (13.0 mL), and 2a (4.0 g, 15.7
mmol) were used. The oily product was purified by dissolving
it in 1:1 hexanes/benzene (+3% Et3N) and quickly flushing it
with the same solvents down a short column of neutral
Oxa h elicen ebisqu in on e 4a . Procedure B. Compound 3a
(8.4 g, 14.8 mmol) in toluene (55 mL) was combined with
p-benzoquinone (48.0 g, 440 mmol) and heated at 100 °C for
48 h. The crude product was divided into two portions, and
each was chromatographed (eluents from 4:1 CH2Cl2/hexanes
to CH2Cl2). The silica gel was washed, and mixed fractions
were rechromatographed on it. This gave 4.5 g (39%) of a
brilliant orange solid (4a , Rf 0.80, CH2Cl2; mp > 225 °C). IR
1
alumina. This gave 8.5 g (96%) of a yellow oil (3a ). H NMR
(acetone-d6, referenced to the acetone peak, 300 MHz): δ 8.40
(d, 2H, 1.6 Hz), 7.87 (dd, 2H, 8.7 Hz), 7.60 (dd, 2H, 8.6 Hz),
5.05 (d, 2H, 2.0 Hz), 4.51 (d, 2H, 1.9 Hz), 1.36 (m, 6H), 1.18
ppm (d, 38H, 7.1 Hz). 13C NMR (acetone-d6, referenced to the
acetone peak, 75 MHz): δ 157.5, 156.7, 134.1, 126.0, 124.8,
118.2, 112.0, 90.3, 18.5, 13.5 ppm.
3,6-Bis[1-(t r iisop r op ylsiloxy)e t h e n yl]d ib e n zot h io-
p h en e (3b). Procedure A. Triisopropylsilyl triflate (8.8 g, 28.5
mmol, 7.7 mL), CH2Cl2 (70 mL), Et3N (11.3 mL), and 2b (3.6
g, 13.4 mmol) were used. The oily product was purified in the
same way as 3a . This gave 7.2 g (91%) of a light yellow oil
(3b). 1H NMR (acetone-d6, referenced to the acetone peak, 300
MHz): δ 8.58 (d, 2H, 1.5 Hz), 7.96 (dd, 2H, 8.5 Hz), 7.85 (dd,
2H, 8.5 Hz), 5.12 (d, 2H, 2.0 Hz), 4.57 (d, 2H, 2 Hz), 1.40 (m,
6H), 1.19 ppm (d, 36H, 7.2 Hz). 13C NMR (acetone-d6, refer-
enced to the acetone peak, 75 MHz): δ 156.4, 140.1, 135.8,
135.3, 124.9, 123.0, 118.5, 90.5, 18.1, 13.1 ppm.
(CCl4) 1663, 1570 cm-1 1H NMR (CDCl3, 300 MHz): δ 8.45
.
(d, 2H, 9.1 Hz), 7.92 (d, 2H, 9.0 Hz), 7.40 (s, 2H), 6.74 (d, 2H,
10.2 Hz), 6.50 (d, 2H, 10.2 Hz), 1.53 (m, 8H), and two doublets
(10.8 Hz) at 1.23 and 1.20 ppm (39H). 13C NMR (CDCl3, 75
MHz): δ 185.9, 182.7, 159.1, 156.8, 140.1, 135.6, 133.5, 127.8,
127.6, 124.8, 123.1, 122.1, 114.6, 107.1, 18.0, 13.0 ppm. UV-
vis (CH2Cl2, c ) 3.2 × 10-5 M), λmax (log ꢀ): 490 (3.82), 390
(3.72), 340 (4.22), 319 (4.25), 260 (4.37), 240 nm (4.37). Anal.
Calcd for C46H52O7Si2: C, 71.46; H, 6.79. Found: C, 71.57; H,
6.78.
Also isolated in the chromatographic procedure was 2.5 g
(22%) of orange/red solid 5a (Rf 0.64, CH2Cl2; mp > 225 °C).
1H NMR (CDCl3, 300 MHz): δ 9.97 (s, 1H), 8.62 (d, 1H, 9.2
Hz), 8.28 (s, 1H), 7.96 (d, 1H, 9.1 Hz), 7.57 (s, 1H), 7.50 (s,
1H), 7.12 (d, 1H, 10.2 Hz), 6.99 (d, 1H, 10.1 Hz), 6.96 (d, 1H,
10.1 Hz), 6.90 (d, 1H, 10.1 Hz), 1.53 (m, 9H), and a pair of
doublets (10.2 and 10.3 Hz, respectively) at 1.22 and 1.19 ppm
(42H). 13C NMR (CDCl3, 75 MHz): δ 187.0, 186.2, 183.6, 160.5,
159.1, 158.8, 157.9, 141.2, 140.8, 135.6, 135.3, 135.2, 134.2,
131.0, 127.9, 127.2, 126.5, 125.6, 123.3, 120.3, 119.0, 115.2,
108.5, 107.6, 106.0, 18.3, 18.1, 13.3, 13.1 ppm. UV-vis
(CH3CN, c ) 3.4 × 10-5 M), λmax (log ꢀ): 490 (3.75), 410 (3.96),
343 (sh, 4.10), 320 (4.20), 260 (4.34), 210 nm (4.35).
3,6-Bis[1-(t r iisop r op ylsiloxy)-et h en yl]-N-d od ecylca r -
ba zole (3d ). Procedure A. Triisopropylsilyl triflate (21.8 g, 71
mmol, 19.1 mL), CH2Cl2 (160 mL), Et3N (28 mL), and 2d (14.2
g, 34 mmol) were used. The oily product was purified in the
same way as 3a . This gave 24.5 g (99%) of a light yellow oil
(3d ). 1H NMR (acetone-d6, referenced to the acetone peak, 300
MHz): δ 8.46 (d, 2H, 1.4 Hz), 7.81 (dd, 2H, 1.7 and 6.9 Hz),
7.52 (d, 2H, 8.8 Hz), 4.97 (d, 2H, 1.6 Hz), 4.44 (d, 2H, 1.6 Hz),
4.40 (t, 2H, 7 Hz), 1.87 (m, 2H), 1.42 (m, 6H), 1.21 (m, 52H),
0.85 ppm (t, 3H, 7 Hz). 13C NMR (acetone-d6, referenced to
the acetone peak, 75 MHz): δ 157.7, 141.8, 129.9, 124.4, 123.5,
117.7, 109.5, 88.8, 43.6, 32.6, 29.6 (m), 27.8, 23.3, 18.6, 14.4,
13.6 ppm.
Gen er a l P r oced u r e B. P r ep a r a tion of Heter o[7]-
h elicen ebisqu in on es. Aza h elicen ebisqu in on e 4c. A flask
containing 3c (9.1 g, 15.8 mmol) and p-benzoquinone (51.3 g,
474 mmol) was fitted with a reflux condenser and then
evacuated and filled with N2 three times. Toluene (60 mL) was
syringed in, and the mixture was heated in an oil bath at 90
°C for 11 h. The reaction mixture was then cooled to room
temperature, and CH2Cl2 was added. The mixture was filtered
through Celite, and the solvent was evaporated. Sublimation
at 120 °C under a vacuum of ca. 1 mmHg transferred excess
benzoquinone into a cold trap. The crude material was divided
into two equal portions, and each was chromatographed
(eluents from 1:1 hexanes/CH2Cl2 to 20:1 CH2Cl2/ethyl acetate)
on a 600 mL coarse fritted funnel packed with silica gel. The
silica gel was washed with acetone until it was colorless, and
it was then reused. The mixed fractions were rechromato-
graphed similarly on the recycled silica gel. The resulting red/
purple solid (Rf 0.64, CH2Cl2), after it had been heated
overnight in a vacuum at 120 °C, amounted to 6.5 g (53%) of
4c (mp > 225 °C). IR (CCl4) 1663, 1570 cm-1. 1H NMR (CDCl3,
300 MHz): δ 8.32 (d, 2H, 9.0 Hz), 7.74 (d, 2H, 9.0 Hz), 7.29 (s,
2H), 6.66 (d, 2H, 10.1 Hz), 6.39 (d, 2H, 10.1 Hz), 4.07 (s, 3H),
1.51 (m, 6H), and a pair of doublets (10.4 Hz) at 1.21 and 1.20
ppm (37H). 13C NMR (CDCl3, 75 MHz): δ 186.2, 182.0, 159.4,
141.0, 140.3, 135.1, 133.7, 127.4, 126.4, 123.3, 121.3, 119.5,
112.9, 106.6, 29.6, 18.1, 13.1 ppm. UV-vis (CH3CN, c ) 3.7 ×
10-5 M), λmax (log ꢀ): 500 (3.56), 420 (3.77), 350 (4.13), 335
(4.13), 310 (4.19), 285 (sh, 4.25), 260 nm (4.29). Anal. Calcd
for C47H55NO6Si2: C, 71.80; H, 7.07; N, 1.78. Found: C, 71.67;
H, 6.93; N, 1.73.
Th ia h elicen ebisqu in on e 4b. Procedure B. Compound 3b
(7.1 g, 12 mmol) in toluene (45 mL) was combined with
p-benzoquinone (39 g, 360 mmol) and heated at 110 °C for 24
h. This gave, after chromatography as for 4c, 3.1 g (33%) of
orange solid 4b (Rf 0.84, CH2Cl2; mp > 225 °C). IR (CCl4) 1663,
1
1570 cm-1. H NMR (CDCl3, 300 MHz) δ 8.32 (d, 2H, 8.7 Hz),
8.01 (d, 2H, 8.7 Hz), 7.37 (s, 2H), 6.61 (d, 2H, 10.1 Hz), 6.11
(d, 2H, 10.1 Hz), 1.53 (m, 7H), 1.22 ppm (m, 38H). 13C NMR
(CDCl3, 75 MHz) δ 185.5, 180.8, 159.7, 141.3, 140.3, 134.3,
132.9, 128.9, 127.5, 123.4, 122.1, 121.4, 107.1, 18.1, 13.0 ppm.
UV-vis (CH3CN, c ) 3.8 × 10-5 M), λmax (log ꢀ): 500 (3.69),
400 (3.92), 330 (4.20), 250 nm (4.31). Anal. Calcd for C46H52O6-
SSi2: C, 69.99; H, 6.65. Found: C, 69.83; H, 6.49.
Also isolated was 1.8 g (19%) of orange/red solid 5b (Rf 0.63,
1
CH2Cl2; mp > 225 °C). H NMR δ (CDCl3, 300 MHz): δ 10.24
(s, 1H), 8.63 (s, 1H), 8.47 (d, 1H, 8.8 Hz), 8.06 (d, 1H, 8.8 Hz),
7.58 (s, 1H), 7.48 (s, 1H), 6.97 (m, 2H), 6.91 (m, 2H), 1.53 (m,
13H), 1.20 (m, 67H!); 13C NMR (CDCl3, 75 MHz): δ 186.9,
186.1, 186.0, 183.7, 158.7, 158.5, 145.2, 141.9, 141.0, 140.5,
136.7, 135.5, 135.3, 135.0, 134.1, 130.6, 129.3, 127.0, 123.7,
123.0, 121.5, 121.2, 119.7, 108.0, 106.1, 18.2, 18.0, 13.0 ppm
(two peaks). UV-vis (CH3CN, c ) 3.9 × 10-5 M), λmax (log ꢀ):
490 (3.60), 420 (3.81), 330 (sh, 4.10), 290 (4.26), 260 (4.27),
230 nm (4.26).
Aza h elicen ebisqu in on e 4d . Procedure B. Compound 3d
(24.5 g, 33.5 mmol) in toluene (125 mL) was combined with
p-benzoquinone (108 g, 1 mol) and heated at 85 °C for 14 h.
The reaction mixture was then diluted with CH2Cl2 and
filtered through Celite, and the solvent was evaporated. The
residue was triturated with 200 mL of pentanes and filtered
on Celite. The solids were washed with pentanes until the
filtrate came through clear. The collected solid, containing 4d
and benzoquinone, was washed from the Celite with CH2Cl2,
and the solvent was evaporated. Benzoquinone was removed
by sublimation under vacuum at 100 °C for several hours.
Also isolated in this chromatographic procedure was 2.9 g
(23%) of a green/black solid (5c, Rf 0.44, CH2Cl2; mp > 225
1
°C). H NMR (CDCl3, 300 MHz) δ 9.77(s, 1H), 8.50 (d, 1H, 9.1
Hz), 8.33 (s, 1H), 7.74 (d, 1H, 9.1 Hz), 7.43 (s, 1H), 7.38 (s,

3676 J . Org. Chem., Vol. 64, No. 10, 1999
Dreher et al.
Obtained was 16.0 g (50%) of a red/purple solid (mp 210-211
into a N2-purged flask with condenser containing 9c (0.45 g,
0.77 mmol), Zn (0.78 g, 11.9 mmol), and (S)-(-)-camphanoyl
chloride (2.5 g, 11.5 mmol). The reaction mixture was heated
at reflux for 1 h, whereupon it turned yellow. It was cooled to
room temperature and filtered through Celite. After the filtrate
had been diluted with CH2Cl2, washed twice with 1 N HCl
and twice with saturated aqueous NaHCO3, and dried
(Na2SO4), the solvent was removed, giving a yellow/orange
foam. Chromatography on silica gel (eluents from toluene to
5:1 toluene/THF) gave the levorotatory diastereomer, (M)-
(-)-10c (0.45 g, 91%), mp > 225 °C, and the dextrorotatory
diastereomer, (P)-(+)-10c (0.46 g, 92%), mp > 225 °C. The
latter was purified further by chromatography. The same
solvents were used.
1
°C). IR (CCl4) 1663, 1569 cm-1. H NMR (CDCl3, 400 MHz) δ
8.30 (d, 2H, 9.0 Hz), 7.73 (d, 2H, 9.0 Hz), 7.27 (s, 2H), 6.65 (d,
2H, 10.1 Hz), 6.40 (d, 2H, 10.1 Hz), 4.47 (t, 2H, 7.6 Hz), 2.02
(m, 2H), 1.51 (m, 5H), 1.40 (m, 1H), 1.20 (m, 48H), 0.87 ppm
(t, 3H, 7.0 Hz). 13C NMR (CDCl3, 75 MHz) δ 186.3, 181.9, 159.3,
140.5, 140.3, 135.1, 133.6, 127.5, 123.2, 121.2, 119.6, 113.0,
106.4, 43.7, 31.2, 30.1, 29.5, 29.3 (m), 27.4, 22.7, 18.1, 14.1,
13.0 ppm. Anal. Calcd for C58H77O6NSi2: C, 74.06; H, 8.27; N,
1.49. Found: C, 73.84; H, 8.28; N, 1.37.
Gen er a l P r oced u r e C. Rep la cem en t of Siloxy w ith
Alk yl Sid e Ch a in s. Aza h elicen ebisqu in on e 9c. A flask
containing 4c (1.5 g, 1.9 mmol) and CsF (1.16 g, 7.6 mmol)
was evacuated and filled with N2 three times. n-Butyl iodide
(8.7 g, 47.5 mmol, 5.4 mL) was added by syringe, and DMF
(90 mL) was added through a cannula. The reaction mixture
was heated to 70 °C for 3 h, cooled to room temperature, and
poured into H2O (0.5 L). The resulting mixture was filtered
through Celite and washed with H2O (200 mL). The purple/
red solid was rinsed from the Celite with CH2Cl2, washed with
H2O (3 × 300 mL), dried (Na2SO4), and to remove trace
impurities, poured onto ca. 50 g of silica gel in a fritted funnel
and washed from it with CH2Cl2. The solvent was evaporated,
giving 1.0 g (94%) of a red/purple solid (9c, mp > 225 °C). IR
The 1H NMR spectra of the diastereomers would have
detected 3% of (P)-(+)-10c in the sample of (M)-(-)-10c and
1% of (M)-(-)-10c in the sample of (P)-(+)-10c. Accordingly,
the enantiomeric purities of (+)- and (M)-(-)-10c were g99%
and g97%, respectively. Similar analyses (see below) showed
the enantiomeric purities of (+)- and (M)-(-)-10a to be g99%
and g98%, respectively, of both (+)- and (M)-(-)-10b to be
g99%, and of both (P)-(+)-10d and (M)-(-)-10d to be g99%.
(M)-(-)-10c: [R]D -280 (c 0.060, CH2Cl2). IR (CCl4) 1799,
1752 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.76 (d, 2H, 8.8 Hz),
7.93 (d, 2H, 8.8 Hz), 7.17 (d, 2H, 8.4 Hz), 7.11 (s, 2H), 6.00 (d,
2H, 8.4 Hz), 4.33 (m, 4H), 4.26 (s, 3H), 2.76 (m, 2H), 2.43 (m,
2H), 2.12 (m, 2H), 2.04 (m, 4H), 1.89 (m, 2H), 1.70 (m, 4H),
1.35 (s, 6H), 1.31 (s, 6H), 1.26 (s, 7H), 1.15 (m, 2H), 1.09 (t,
3H, 7.3 Hz), 0.79 (s, 6H), 0.41 (m, 2H), 0.27 (s, 6H), 0.19 ppm
(m, 2H). 13C NMR (CDCl3, 75 MHz): δ 178.0, 177.3, 166.5,
164.5, 155.1, 144.3, 141.3, 139.2, 127.0, 124.7, 122.7, 121.2,
120.8, 120.0, 119.6, 114.9, 108.6, 93.3, 91.5, 89.3, 68.2, 55.1,
54.6, 53.9, 53.6, 31.5, 31.2, 29.8, 29.1, 28.3, 28.0, 19.7, 17.3,
17.1, 16.0, 15.1, 14.0, 9.9, 9.5 ppm. UV-vis (CH3CN, c ) 2.4
× 10-5 M): λmax (log ꢀ) 417 (3.81), 396 (3.72), 330 (4.23), 300
(4.29), 273 (4.36), 230 nm (4.34). CD (c ) 2.4 × 10-5, CH3CN),
nm (∆ꢀ): 210 (-137), 245 (306), 281 (-253), 294 (-36), 335
(-204), 418 (75). Anal. Calcd for C77H83O18N: C, 70.56; H, 6.40;
N, 1.07. Found: C, 70.26; H, 6.48; N, 0.96.
(CCl4) 1662, 1573 cm-1 1H NMR (CDCl3, 300 MHz): δ 8.34
.
(d, 2H, 9.0 Hz), 7.72 (d, 2H, 9.0 Hz), 7.28 (s, 2H), 6.69 (d, 2H,
10.1 Hz), 6.43 (d, 2H, 10.1 Hz), 4.35 (m, 4H), 4.07 (s, 3H), 1.98
(m, 4H), 1.65 (m, 4H), 1.08 ppm (t, 6H, 7.4 Hz). 13C NMR
(CDCl3, 75 MHz): δ 186.4, 182.0, 161.2, 140.9, 140.0, 135.1,
133.9, 126.7, 124.0, 123.1, 120.7, 119.2, 112.8, 99.3, 68.9, 31.1,
29.6, 19.4, 13.9 ppm. Anal. Calcd for C37H31NO6: C, 75.87; H,
5.35; N, 2.38. Found: C, 75.80; H, 5.36; N, 2.57.
Oxa h elicen ebisqu in on e 9a . Procedure C. Compound 4a
(0.70 g, 0.91 mmol), CsF (0.55 g, 3.6 mmol), n-butyl iodide (4.3
g, 22.9 mmol, 2.6 mL), and DMF (30 mL) were used. Obtained
was 0.51 g (99%) of a red solid (9a , mp > 225 °C). IR (CCl4)
1664, 1571 cm-1 1H NMR (CDCl3, 300 MHz) δ 8.48 (d, 2H,
.
9.1 Hz), 7.92 (d, 2H, 9.1 Hz), 7.38 (s, 2H), 6.76 (d, 2H, 10.1
Hz), 6.50 (d, 2H, 10.1 Hz), 4.38 (m, 4H), 2.00 (m, 4H), 1.66 (m,
4H), 1.08 ppm (t, 7H). 13C NMR (CDCl3, 75 MHz) δ 186.1,
182.8, 161.0, 156.7, 139.9, 135.7, 133.8, 127.0, 125.5, 124.5,
122.6, 122.0, 114.6, 100.0, 69.2, 31.1, 19.4, 13.9 ppm. HRMS
(FAB): m/z calcd for C36H28O7: 573.2249, found 573.1910.
Th ia h elicen ebisqu in on e 9b. Procedure C. Compound 4b
(0.50 g, 0.64 mmol), CsF (0.39 g, 2.56 mmol), n-butyl iodide
(2.9 g, 16.0 mmol, 1.8 mL), and DMF (30 mL) were used.
Obtained was 0.34 g (91%) of an orange solid (9b, mp > 225
°C). IR (CCl4) 1664, 1570 cm-1. 1H NMR (CDCl3, 300 MHz): δ
8.34 (d, 2H, 8.8 Hz), 8.03 (d, 2H, 8.7 Hz), 7.37 (s, 2H), 6.65 (d,
2H, 10.1 Hz), 6.21 (d, 2H, 10.1 Hz), 4.37 (m, 4H), 2.02 (m, 4H),
1.68 (m, 5H), 1.10 ppm (t, 7H, 7.4 Hz). 13C NMR (CDCl3, 75
MHz): δ 185.7, 180.8, 161.5, 141.4, 140.1, 134.6, 134.2, 132.8,
127.0, 126.8, 123.4, 122.0, 120.9, 99.9, 69.2, 31.1, 19.4, 13.9
ppm. Anal. Calcd for C36H28O6S: C, 73.44; H, 4.80. Found: C,
73.13; H, 4.95.
(P)-(+)-10c: [R]D +220 (c 0.045, CH2Cl2). IR (CCl4) 1799
cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.69 (d, 2H, 8.8 Hz), 7.99
(d, 2H, 8.9 Hz), 7.13 (d, 2H, 8.4 Hz), 6.99 (s, 2H), 6.02 (d, 2H,
8.3 Hz), 4.33 (m, 2H), 4.32 (m, 3H), 4.24 (m, 2H), 2.82 (m, 2H),
2.46 (m, 2H), 2.15 (m, 2H), 2.04 (m, 4H), 1.92 (m, 2H), 1.71
(m, 3H), three singlets (20H total) at 1.30, 1.27, and 1.26, 1.14
(m, 2H), 1.11 (t, 6H, 7.4 Hz), 0.82 (s, 6H), 0.33 (s, 12H), 0.05
(m, 2H), -0.27 ppm (m, 2H). 13C NMR (CDCl3, 75 MHz): δ
177.7, 177.2, 166.6, 164.2, 155.0, 144.7, 141.5, 140.0, 126.8,
124.6, 121.8, 120.3, 120.2, 119.5, 115.4, 110.0, 93.1, 91.2, 90.0,
68.1, 55.0, 54.5, 54.1, 53.6, 31.3, 31.2, 30.0, 29.2, 28.7, 26.7,
19.8, 17.2, 17.1, 16.1, 13.9, 9.8, 9.4 ppm. UV-vis (CH3CN, c )
2.4 × 10-5 M), λmax (log ꢀ): 417 (3.81), 396 (3.70), 330 (4.18),
300 (4.25), 273 (4.34), 230 nm (4.31). CD (c ) 2.4 × 10-5
,
CH3CN), nm (∆ꢀ): 210 (72), 245 (-160), 281 (135), 294 (19),
335 (94), 418 (-40). Anal. Calcd for C77H83O18N: C, 70.56; H,
6.40; N, 1.07. Found: C, 70.41; H, 6.49; N, 0.97.
Aza h elicen ebisqu in on e 9d . Procedure C. Compound 4d
(0.50 g, 0.53 mmol), CsF (0.32 g, 2.1 mmol), 1-iodododecane
(4.0 g, 13.5 mmol, 3.3 mL), and DMF (26 mL) were used. The
reaction mixture was poured into 100 mL of Et2O and washed
three times with 100 mL of H2O. After it had been dried
(Na2SO4), the solvent was evaporated. Chromatography, elut-
ing first with pure hexanes to remove excess 1-iodododecane
and then with CH2Cl2, gave 0.44 g (86%) of a red/purple solid
Tetr a ca m p h a n a te 10a . Procedure D. Compound 9a (0.35
g, 0.61 mmol), toluene (25 mL), TMEDA (7.2 g, 61 mmol, 9.4
mL), Zn (0.62 g, 9.7 mmol), and (S)-(-)-camphanoyl chloride
(2.0 g, 9.2 mmol) were used. Column chromatograpy on silica
gel (eluents from 10:1 hexanes/ethyl acetate to 1.5:1 hexanes/
ethyl acetate) gave the levorotatory diastereomer, (M)-(-)-10a
(0.34 g, 85%), mp > 225 °C, and the dextrorotatory diastere-
omer, (P)-(+)-10a (0.30 g, 76%), mp > 225 °C. The latter was
purified further by chromatography. The same solvents were
used.
(M)-(-)-10a : [R]D -310 (c 0.027, CH2Cl2). IR (CCl4) 1800,
1753 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.75 (d, 2H, 8.8 Hz),
8.01 (d, 2H, 8.8 Hz), 7.17 (d, 2H, 8.4 Hz), 7.10 (s, 2H), 6.03 (d,
2H, 8.4 Hz), 4.34 (m, 2H), 4.27 (m, 2H), 2.75 (m, 2H), 2.41 (m,
2H), 2.11 (m, 2H), 2.04 (m, 4H), 1.89 (m, 2H), 1.68 (d, 4H, 7.0
Hz), three singlets (20H total) at 1.34, 1.29, and 1.25, 1.17 (m,
2H), 1.08 (t, 6H, 7.3 Hz), 0.82 (m, 2H), 0.82 (s, 6H), 0.35 (s,
6H), 0.27 (m, 2H), 0.25 ppm (s, 6H). 13C NMR (CDCl3, 75
MHz): δ 177.8, 176.9, 166.4, 164.9, 155.1, 154.9, 144.5, 141.3,
1
(9d , mp 208-209 °C). IR (CCl4) 1662 cm-1. H NMR (CDCl3,
300 MHz): δ 8.32 (d, 2H, 9.0 Hz), 7.72 (d, 2H, 9.0 Hz), 7.26 (s,
2H), 6.68 (d, 2H, 10.1 Hz), 6.42 (s, 2H, 10.1 Hz), 4.49 (m, 2H),
4.33 (m, 4H), 2.01 (m, 6H), 1.61 (m, 6H), 1.28 (m, 54H), 0.87
ppm (m, 10H). 13C NMR (CDCl3, 75 MHz): δ 186.5, 182.0,
161.3, 14.5, 140.1, 135.2, 134.0, 126.9, 124.0, 123.2, 120.7,
119.5, 112.9, 99.3, 43.8, 31.9, 30.1, 29.6 (m), 29.4, 27.4, 26.2,
22.7, 14.1 ppm. Anal. Calcd for C64H85NO6: C, 79.69; H, 8.90;
N, 1.45. Found: C, 79.81; H, 9.19; N, 1.40.
Gen er a l P r oced u r e D. P r ep a r a tion of Tetr a ca m p h a -
n a te Ester s. Tetr a ca m p h a n a te 10c. Toluene (35 mL) and
TMEDA (8.9 g, 88 mmol, 11.6 mL) were syringed sequentially

Synthesis of Functionalized Hetero[7]helicenes
J . Org. Chem., Vol. 64, No. 10, 1999 3677
127.4, 124.8, 123.0, 121.4, 121.1, 120.3, 114.6, 110.8, 94.2, 91.4,
89.0, 68.3, 55.1, 54.5, 54.0, 53.8, 31.4, 31.2, 29.0, 28.7, 28.3,
19.6, 17.2, 17.1, 16.0, 15.6, 14.0, 9.8, 9.4 ppm. UV-vis
(CH3CN, c ) 2.4 × 10-5 M), λmax (log ꢀ): 405 (3.96), 386 (3.83),
322 (4.31), 300 (4.39), 260 (sh, 4.51), 210 nm (4.57). CD (c )
2.4 × 10-5, CH3CN), nm (∆ꢀ): 210 (-90), 228 (133), 236 (110),
248 (156), 272 (-197), 292 (15), 314 (-138), 319 (-132), 325
(-160), 408 (40). Anal. Calcd for C76H80O19: C, 70.34; H, 6.23.
Found: C, 70.28; H, 6.28.
(P)-(+)-10a : [R]D +260 (c 0.027, CH2Cl2). IR (CCl4) 1801,
1759 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.70 (d, 2H, 8.8 Hz),
8.08 (d, 2H, 8.8 Hz), 7.16 (d, 2H, 8.4 Hz), 7.02 (s, 2H), 6.07 (d,
2H, 8.4 Hz), 4.34 (m, 2H), 4.24 (m, 2H), 2.79 (m, 2H), 2.45 (m,
2H), 2.14 (m, 2H), 2.03 (m, 4H), 1.92 (m, 2H), 1.70 (m, 4H),
three singlets (22H total) at 1.30, 1.27, and 1.26, 1.10 (t, 6H,
7.4 Hz), 0.84 (s, 6H), 0.52 (m, 2H), 0.34 (s, 6H), 0.31 (s, 6H),
-0.11 ppm (m, 2H). 13C NMR (CDCl3, 75 MHz) 177.6, 176.8,
166.6, 164.6, 155.5, 154.7, 144.8, 141.3, 127.1, 124.3, 124.0,
122.1, 121.8, 121.4, 120.7, 115.4, 112.2, 94.3, 90.9, 89.9, 68.2,
54.9, 54.4, 54.0, 53.7, 31.2, 29.6, 29.0, 28.5, 27.1, 19.6, 17.1,
16.1, 16.0, 13.8, 9.7, 9.3 ppm. UV-vis (CH3CN, c ) 2.4 × 10-5
M), λmax (log ꢀ): 405 (3.96), 386 (3.83), 322 (4.31), 300 (4.39),
260 (sh, 4.51), 225 (sh, 4.49), 210 nm (4.57). CD (c ) 2.4 ×
10-5, CH3CN), nm (∆ꢀ): 210 (102), 228 (-121), 236 (-93), 249
(-160), 272 (203), 292 (-19), 314 (127), 319 (121), 325 (145),
408 (-45). HRMS (FAB): m/z calcd for C76H80O19: 1296.6206,
found 1296.5303.
Tetr a ca m p h a n a te 10b. Procedure D. Compound 9b (0.31
g, 0.52 mmol), toluene (25 mL), TMEDA (6.1 g, 52 mmol, 7.9
mL), Zn (0.52 g, 8.1 mmol), and (S)-(-)-camphanoyl chloride
(1.7 g, 8.1 mmol) were used. Chromatography on silica gel
(eluents from CH2Cl2 to 3:1 CH2Cl2/ethyl acetate) gave the
levorotatory diastereomer, (M)-(-)-10b (0.31 g, 91%), mp >
225 °C, and the dextrorotatory diastereomer, (P)-(+)-10b (0.24
g, 71%), mp > 225 °C. The latter was purified further by
chromatography. The same solvents were used.
(M)-(-)-10b: [R]D -470 (c 0.031, CH2Cl2). IR (CCl4) 1799,
1754 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.71 (d, 2H, 8.5 Hz),
8.12 (d, 2H, 8.5 Hz), 7.07 (d, 2H, 9.4 Hz), 7.04 (s, 1H), 6.09 (d,
2H, 8.4 Hz), 4.36 (m, 2H), 4.22 (m, 2H), 2.72 (m, 2H), 2.41 (m,
2H), 2.10 (m, 2H), 2.04 (m, 4H), 1.87 (m, 2H), 1.67 (m, 4H),
three singlets (22H total) at 1.30, 1.28, and 1.24, 1.08 (t, 6H,
7.4 Hz), 1.00 (m, 2H), 0.43 (s, 6H), 0.32 (s, 6H), -0.10 ppm
(m, 2H). 13C NMR (CDCl3, 75 MHz): δ 177.8, 177.2, 166.1,
164.9, 154.8, 144.4, 141.8, 138.2, 133.1, 127.3, 126.3, 125.4,
122.2, 121.0, 120.9, 120.0, 116.1, 94.7, 91.2, 89.1, 68.3, 55.0,
54.5, 54.1, 53.9, 31.3, 31.2, 29.0, 28.8, 28.3, 19.5, 17.2, 17.0,
16.1, 15.7, 13.9, 9.7, 9.4 ppm. UV-vis (CH3CN, c ) 2.4 × 10-5
M), λmax (log ꢀ): 420 (3.68), 335 (4.28), 320 (4.31), 306 (4.32),
276 (4.50), 260 nm (sh, 4.45). CD (c ) 2.4 × 10-5, CH3CN),
nm (∆ꢀ): 210 (-161), 230 (101), 250 (268), 281 (-198), 338
(-213), 418 (67). Anal. Calcd for C76H80O18S: C, 69.48; H, 6.15.
Found: C, 69.21; H, 6.08.
levorotatory diastereomer, (M)-(-)-10d (0.25 g, 75%), mp 159-
160 °C, and the dextrorotatory diastereomer, (P)-(+)-10d (0.27
g, 77%), mp 163-165 °C. The latter was purified further by
chromatography. The same solvents were used.
(M)-(-)-10d : [R]D -300 (c 0.057, CH2Cl2). IR (CCl4) 1799,
1750 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.74 (d, 2H, 8.8 Hz),
7.91 (d, 8.8 Hz), 7.16 (d, 2H, 8.5 Hz), 7.10 (s, 2H), 6.0 (d, 8.5
Hz), 4.69 (m, 2H), 4.30 (m, 4H), 2.77 (m, 2H), 2.43 (m, 2H),
2.10 (m, 2H), 2.05 (m, 6H), 1.89 (m, 2H), 1.31 (m, 72H), 1.11
(m, 2H), 0.89 (m, 9H), 0.78 (s, 6H), 0.45 (m, 2H), 0.29 (s, 6H),
0.13 (m, 2H), 0.03 ppm (s, 6H). 13C NMR (CDCl3, 75 MHz): δ
177.9, 177.1, 166.4, 164.5, 155.1, 144.3, 141.3, 138.5, 127.0,
124.8, 122.6, 121.1, 120.8, 119.9, 119.5, 114.7, 108.7, 93.2, 91.4,
89.2, 68.5, 55.1, 54.5, 53.9, 53.5, 43.5, 31.9, 31.2, 29.9, 29.6
(m), 22.7, 17.3, 17.1, 16.0, 15.3, 14.1, 9.8, 9.5 ppm. UV-vis
(CH3CN, c ) 2.6 × 10-5 M), λmax (log ꢀ): 417 (3.93), 397 (3.84),
334 (4.37), 300 (4.45), 280 (sh, 4.52), 273 (4.53), 230 (sh, 4.51),
210 nm (4.58). CD (c ) 2.6 × 10-5, CH3CN), nm (∆ꢀ): 210
(-70), 245 (153), 281 (-137), 294 (-15), 335 (-105), 418 (38).
Anal. Calcd for C104H137NO18
: C, 73.93; H, 8.19; N, 0.83.
Found: C, 73.98; H, 8.29; N, 0.70.
(P)-(+)-10d : [R]D +220 (c 0.065, CH2Cl2). IR (CCl4) 1799
cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.71 (d, 2H, 8.8 Hz), 7.99
(d, 2H, 8.8 Hz), 7.16 (d, 2H, 8.3 Hz), 7.01 (s, 2H), 6.02 (d, 2H,
8.3 Hz), 4.76 (t, 2H, 7.3 Hz), 4.35 (m, 2H), 4.24 (m, 2H), 2.84
(m, 2H), 2.49 (m, 2H), three multiplets (11H total) at 2.17, 2.07,
and 1.95, 1.50 (m, 6H), 1.30 (m, 77H), 1.15 (m, 2H), 0.92 (m,
9H), 0.86 (s, 6H), 0.39 (s, 6H), 0.32 (s, 6H), 0.10 (m, 2H), -0.39
ppm (m, 2H). 13C NMR (CDCl3, 75 MHz): δ 177.6, 177.1, 166.5,
164.3, 154.9, 144.7, 141.4, 139.1, 126.8, 124.6, 121.8, 120.3,
120.1, 119.3, 115.5, 110.0, 93.1, 91.1, 90.0, 68.4, 54.9, 54.5, 54.1,
53.6, 43.7, 31.9, 31.1, 29.6 (m), 29.5, 29.4, 29.1, 28.6, 27.4, 26.8,
22.7, 17.2, 17.1, 16.1, 14.1, 9.8, 9.4 ppm. UV-vis (CH3CN, c )
2.5 × 10-5 M): λmax (log ꢀ) 417 (3.93), 397 (3.84), 3340 (4.37),
300 (4.45), 280 (4.52), 273 (4.53), 230 (4.51), 210 nm (4.58).
CD (c ) 2.5 × 10-5, CH3CN), nm (∆ꢀ): 210 (72), 245 (-145),
281 (132), 294 (15), 335 (83), 418 (-39). Anal. Calcd for
C
104H137NO18: C, 73.93; H, 8.19; N, 0.83. Found: C, 73.82; H,
8.23; N, 0.91.
Gen er a l P r oced u r e E. P r ep a r a tion of Non r a cem ic
Heter oh elicen es 9 fr om Tetr a ester s 10. (M)-Aza h eli-
cen ebisqu in on e 9c. MeLi in Et2O (9.9 mL, 1.6 M, 7.1 mmol)
was added to a solution of (M)-(-)-10c (0.43 g, 0.32 mmol) in
THF (40.0 mL) that had been cooled to -78 °C in a dry ice/
acetone bath. After several minutes, the bath was removed,
and after the reaction mixture had warmed to room temper-
ature, it was stirred for 1 h. Saturated aqueous NH4Cl was
added to quench the reaction. The mixture was then washed
once with aqueous HCl (1 N) and twice with H2O and dried
(Na2SO4). Chloranil (0.260 g, 1.06 mmol) was added, and the
reaction mixture was stirred for 15 min at room temperature,
whereupon it turned from bright yellow to red/brown. After
this mixture had been filtered, it was washed twice with
NaHCO3 and dried (Na2SO4). The solvent was stripped, and
the dark solid was chromatographed (eluents from 1:1 hexanes/
CH2Cl2 to CH2Cl2), giving (M)-9c (0.12 g, 63%), a red/purple
solid (mp > 225 °C). UV-vis (CH3CN, c ) 5.4 × 10-5 M): λmax
(log ꢀ) 500 (3.55), 420 (3.78), 350 (4.06), 340 (sh, 4.00), 305
(sh, 4.09), 260 nm (4.16). CD (c ) 5.4 × 10-5, CH3CN), nm
(∆ꢀ): 217 (95), 253 (-105), 284 (47), 308 (-32), 330 (2), 352
(-29), 366 (-19), 389 (-26), 445 (5), 569 (-8). The same
reaction conditions converted (P)-(+)-10c into (P)-9c (0.21 g,
85%). The 1H and 13C NMR spectra of (M)-9c, (P)-9c, and
racemic 9c were identical.
(M)-9a . Procedure E. MeLi in Et2O (10.0 mL, 1.6 M, 6.3
mmol) was added to (M)-(-)-10a (0.33 g, 0.25 mmol) in THF
(16 mL) at -78 °C. The mixture was warmed to room
temperature for 1 h, and saturated aqueous NH4Cl was added.
Chloranil oxidation and chromatography gave (M)-9a (0.12 g,
80%), mp 225 °C. UV-vis (CH3CN, c ) 5.4 × 10-5 M), λmax
(log ꢀ): 490 (3.77), 390 (3.68), 340 (4.17), 314 (4.19), 255 nm
(4.26). CD (c ) 5.4 × 10-5, CH3CN), nm (∆ꢀ): 212 (98), 249
(-108), 271 (48), 288 (-44), 313 (48), 341 (-35), 358 (-18),
402 (-48), 487 (18). (P)-(+)-10a similarly gave (P)-9a (0.11 g,
(P)-(+)-10b: [R]D +460 (c 0.031, CH2Cl2). IR (CCl4) 1800,
1754 cm-1. 1H NMR (CDCl3, 400 MHz): δ 8.61 (d, 2H, 8.5 Hz),
8.17 (d, 2H, 8.5 Hz), 7.06 (d. 2H, 8.4 Hz), 6.99 (s, 2H), 6.06 (d,
2H, 8.4 Hz), 4.25 (m, 4H), 2.80 (m, 2H), 2.43 (m, 2H), 2.14 (m,
2H), 2.03 (m, 4H), 1.93 (m, 2H), 1.60 (m, 4H), 1.50 (m, 2H),
three singlets (16H total) at 1.27, 1.25, and 1.22, 1.11 (t, 6H,
7.4 Hz), 0.91 (s, 6H), 0.63 (m, 2H), 0.48 (s, 6H), 0.43 (s, 6H),
0.10 ppm (m, 2H). 13C NMR (CDCl3, 75 MHz): δ 177.7, 177.0,
166.2, 164.8, 154.6, 144.8, 142.1, 139.7, 133.2, 127.5, 125.9,
125.4, 122.1, 121.9, 121.0, 120.9, 117.4, 94.7, 91.2, 90.0, 68.2,
55.0, 54.7, 54.3, 53.9, 31.3, 30.8, 29.2, 28.8, 27.4, 19.8, 17.2,
16.9, 16.2 (two peaks), 14.0, 9.8, 9.5 ppm. UV-vis (CH3CN, c
) 2.4 × 10-5 M): λmax (log ꢀ) 420 (3.68), 335 (4.28), 320 (4.31),
306 (4.30), 276 (4.45), 260 nm (sh, 4.42). CD (c ) 2.4 × 10-5
,
CH3CN), nm (∆ꢀ): 208 (110), 230 (-26), 253 (-141), 280 (81),
300 (29), 342 (116), 423 (-28). Anal. Calcd for C76H80O18S: C,
69.48; H, 6.15. Found: C, 69.15; H, 6.12.
Tetr a ca m p h a n a te 10d . Procedure D. Compound 9d (0.40
g, 0.42 mmol), toluene (20 mL), TMEDA (4.9 g, 42 mmol, 6.3
mL), Zn (0.42 g, 6.5 mmol) and (S)-(-)-camphanoyl chloride
(1.4 g, 6.3 mmol) were used. Chromatography on silica gel
(eluents from hexanes to 3:1 hexanes/ethyl acetate) gave the

3678 J . Org. Chem., Vol. 64, No. 10, 1999
Dreher et al.
87%), mp > 225 °C. The 1H and 13C NMR of (M)-9a , (P)-9a ,
and racemic 9a were identical.
(M)-(-)-9b. Procedure E. n-BuLi in hexanes (2.0 mL, 2.6
M, 5.2 mmol) was added to (M)-(-)-10b (0.26 g, 0.19 mmol) in
THF (15 mL) at -78 °C. After the reaction mixture had
remained at -78 °C for 20 min, saturated aqueous NH4Cl was
added. Chloranil oxidation followed by silica gel chromatog-
350 (3.98), 335 (3.97), 305 (sh, 4.00), 260 nm (4.05). CD (c )
5.8 × 10-5, CH3CN), nm (∆ꢀ): 216 (95), 253 (-109), 284 (46),
308 (-28), 330 (3), 352 (-28), 366 (-19), 389 (-25), 445 (7),
569 (-7). (P)-(+)-10d similarly gave (P)-9d (0.11 g, 84%). The
1H and 13C NMR of (M)-9d , (P)-9d , and racemic 9d were
identical.
raphy gave (M)-(-)-9b (0.074 g, 65%), mp > 225 °C. [R]D
)
Ack n ow led gm en t. We thank the NSF for grant
support (CHE98-02316) and Columbia University’s I.
I. Rabi Scholars Program for its support of D.J .W.
-1300 (c 0.030, CH2Cl2); UV-vis (CH3CN, c ) 5.4 × 10-5 M),
λmax (log ꢀ): 490 (3.61), 405 (3.85), 335 (4.08), 320 (4.07), 280
(sh, 4.21), 250 nm (4.23). CD (c ) 5.4 × 10-5, CH3CN), nm
(∆ꢀ): 218 (71), 234 (71), 256 (-111), 283 (53), 303 (-41), 328
(-4), 347 (-41), 363 (-21). (P)-(+)-10b similarly gave (P)-(+)-
9b (0.095 g, 75%), mp > 225 °C. [R]D ) +1350 (c 0.030,
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of 2a -d , 3a -d , 4a -d , 5a -c, 9a -d , (P)-(+)-10a -d ,
and (M)-(-)-10a -d ; IR spectra of 3c, 4a -d , 9a -d , (P)-(+)-
10a -d , and (M)-(-)-10a -d ; UV spectra of 4a -c, 5a -c, (P)-
9a -d , (M)-9a -d , (P)-(+)-10a -d , and (M)-(-)-10a -d ; and CD
spectra of (P)-9a -d , (M)-9a -d , (P)-(+)-10a -d , and (M)-(-)-
10a -d . This material is available free of charge via the
Internet at http://pubs.acs.org.
1
CH2Cl2). The H and 13C NMR spectra of (M)-(-)-9b, (P)-(+)-
9b, and racemic 9b were identical.
(M)-9d . Procedure E. MeLi in Et2O (2.0 mL, 1.6M, 3.0 mmol)
was added to (M)-(-)-10d (0.21 g, 0.12 mmol) in THF (14 mL)
at -78 °C. The mixture was warmed to room temperature for
1 h, and saturated aqueous NH4Cl was added. Chloranil
oxidation and chromatography gave (M)-9d (0.11 g, 88%). UV-
vis (CH3CN, c ) 5.8 × 10-5), λmax (log ꢀ): 500 (3.53), 420 (3.76),
J O990065O