Charge Delocalization in Benz[a]anthrecenium Cations
J . Org. Chem., Vol. 63, No. 21, 1998 7285
(CH), 125.1 (CH), 124.9 (CH), 73.0 (COHMe), 43.3 (CH2), 31.7
(CH2), 28.8 (CH2), 20.2 (Me); 1H NMR δ 9.40 (s), 8.14 (s), 7.94,
7.81, 7.60, 7.36, 6.92, 2.74 (CH2), 2.17 (CH2), 2.01 (CH2), 1.81
(Me).
In summary, we have provided the first direct study
of a series of arenium ions and carbocations/carboxonium
ions in the BA series. Detailed NMR studies and charge
delocalization mapping point to distinct anthracenium
ion character. For carbocations derived from potent
carcinogens and those that could be considered simple
models for the potent bay-region and K-region epoxides
as well as cholanthrylene epoxide, the unifying pattern
is one where positive charge resides at the C-4a/C-6/C-
7/C-8/C-10/C-11a/C-12a positions.
Syn th esis of 9-OH. LiAlH4 (38 mg, 1 mmol) was added to
a dry ether (50 mL) solution of 10 (70 mg, 0.26 mmol) at room
temperature, and the reaction mixture was stirred for 18 h.
After addition of methanol (5 mL) to quench excess LAH, the
reaction mixture was poured into 1 N aqueous HCl (100 mL)
and extracted with ether. After removal of solvent, the product
was purified by column chromatography using chloroform
(yield 67%; MS m/z 222, M+): 13C NMR δ 135.6 (C), 131.4 (C),
129.1 (CH), 128.5 (C), 127.5 (CH), 125.2 (CH), 124.6 (CH),
124.5 (CH), 66.7 (CHOHMe), 23.1 (Me); 1H NMR δ 8.38 (2H),
8.08 (s,1H), 7.75 (2H), 7.28 (4H), 6.02 (q), 2.94 (OH),1.59 (d,
Me).
Syn th esis of 2 (Lit. Ref 30). DDQ (227 mg, 1 mmol) was
added to a dry benzene (50 mL) solution of 5-OH, and the
mixture was refluxed for 6 h under Ar atmosphere. It was
then cooled to room temperature, the resulting precipitate was
filtered off, and the benzene layer was washed twice with
water. After removal of the benzene, the product was sepa-
rated by column chromatography using hexane (yield 40%).
Ca tion Gen er a tion fr om Hyd r oca r bon s a n d Keton es.
Using a HV-line, SO2ClF (0.3 mL) was condensed into a 5 mm
NMR tube containing the substrate (30 mg). After addition
of 0.1 mL of CD2Cl2 (NMR lock and reference), FSO3H (5 drops)
was added to the resulting slurry at dry ice temperature under
an argon atmosphere with vigorous (vortex) mixing. For
generation of 6H22+, 5 drops of FSO3H-SbF5 (4:1) was used
(at dry ice acetone temperature). The monocation 6H+ was
generated at room temperature by addition of either TFAH
(0.3 mL) or TFAH (0.3 mL)-H2SO4 (5 drops) mixture together
with CD2Cl2 (0.1 mL).
Exp er im en ta l Section
Compounds 1, 3, 4, 6, and 10 were purchased from Aldrich
and used without further purification after determining (by
NMR) that their purities were no less than 98%.
FSO3H (Allied) and SbF5 (Aldrich or Fluorochem) were
doubly distilled in an all-glass distillation unit under argon
and stored in Nalgen bottles with Teflon cap-seals under argon.
SO2ClF was prepared from SO2Cl2 with NH4F and TFAH
using a modified procedure of Prakash et al.29 The Hyperchem
package (hypercube 1994) was used for energy minimization
and AM1 calculations.
Syn th esis of 8.6 AlCl3 (200 mg, 1.5 mmol) was added to a
solution of BA (228 mg, 1 mmol) and CH3COCl (100 mg, 1.3
mmol) in dry 1,2-dichloroethane (30 mL) at room temperature,
and the reaction mixture was stirred for 5 h; it was then
poured into ice-water and extracted with CHCl3. After
removal of the CHCl3 and 1,2-dichloroethane, the product was
isolated and purified by column chromatography using hex-
ane-chloroform (yield 95%): 13C NMR δ 208.3 (CO),137.2
(CCOMe),129.0 (CH),128.7 (CH),128.6 (CH),127.4 (2CH), 127.0
(CH),125.9 (CH),124.1 (CH),122.9 (2CH),122.8 (CH),131.3 (C),-
P r ep a r a tion of Ca r boca tion s fr om Ca r bin ols. Using
a HV-line, SO2ClF (0.3 mL) was first condensed into a 5 mm
NMR sample, and then five drops of FSO3H was added to this
NMR tube at atmospheric pressure at dry ice/acetone tem-
perature under an argon atmosphere. Finally, a CD2Cl2 (0.1
mL) solution of the alcohol (30 mg) was directly added to this
cold tube with efficient mixing (vortex) to generate the
carbocations.
1
130.2 (C),128.3 (C), 128.0 (C),126.9 (C),125.3 (C); H NMR δ
9.16 (s), 8.78, 8.11, 7.84, 7.81, 7.67, 7.63, 7.62, 7.59, 7.56 (2H),
2.80 (Me).
Syn th esis of 7-OH. LiAlH4 (76 mg, 2 mmol) was added to
a dry ether solution (20 mL) of 8 (220 mg, 1 mmol) at room
temperature. After the mixture was stirred for 5 h at room
temperature, methanol (5 mL) was added to destroy excess
LAH, after which the reaction mixture was poured into 1 N
aqueous HCl (200 mL) and extracted with ether. After
removal of ether, the product was purified by column chro-
matography using chloroform as solvent (yield 77%; MS m/z
272, M+ ): 13C NMR δ 136.1 (C), 131.8 (C), 131.1 (C), 130.8
(C), 129.5 (CH), 129.1 (C), 128.2 (CH), 127.6 (C), 127.0 (CH),
126.9 (CH), 126.8 (CH), 125.7 (CH), 125.0 (CH), 124.5 (CH),
123.4 (CH), 122.9 (CH), 122.5 (CH), 67.2 (CHOHMe), 23.5 (Me);
1H NMR δ 9.01 (s), 8.71, 8.59, 8.37, 8.0, 7.76, 7.61, 7.58, 7.52,
7.47, 6.29, 2.31 (OH), 1.83 (Me).
Syn th esis of 5-OH. MeLi (1.4 M, 7.6 mL, 3.64 mmol) was
added to a dry ether (100 mL) solution of 6 (186 mg, 0.76 mmol)
at 0 °C under Ar atmosphere. The reaction mixture was then
warmed to room temperature and stirred for 12 h after which
MeOH (5 mL) was added to quench excess MeLi; the reaction
mixture was poured into water and extracted with ether. After
removal of ether, the product was purified by column chro-
matography with chloroform (yield 76%): 13C NMR δ 135.7
(C), 134.0 (C), 131.9 (C), 131.1 (C), 130.2 (C), 129.3 (C), 129.0
(CH), 128.1 (CH), 127.5 (CH), 127.3 (CH), 126.5 (CH), 126.4
Qu en ch in g of 7+ w ith MeOH. The SO2ClF solution of 7+
was poured into dry CH3OH at 0 °C; the product was extracted
with CHCl3, and the crude reaction mixture was analyzed
directly by NMR: 1H NMR δ 9.20 (s), 8.85 (d), 8.39 (m), 7.84
(d), 7.69-7.55 (7H), 5.93 (q, CHOMe), 3.22 (s,OMe), 1.89 (d,
Me).
Ack n ow led gm en t. Support of our work in the area
of mechanistic carcinogenesis of PAHs by the NCI of
NIH (Grant R15 CA63595-01A1) is gratefully acknowl-
edged.
Su p p or t in g In for m a t ion Ava ila b le: Representative
1H,13C, and 2D NMR spectra of the carbocations and carboxo-
nium ions (29 pages). This material is contained in libraries
on microfiche, immediately follows the article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering.
J O980722X
(29) Reddy, P. V.; Bellow, D. R.; Prakash, G. K. S. J . Fluorine Chem.
1992, 56, 195-197.
(30) Dunning, W. F.; Curtis, M. R. J . Natl. Cancer. Inst. 1960, 25,
387-391.