Total synthesis of heliophenanthrone

Article abstract of DOI:10.1021/jo050400a

The total synthesis of rac-heliophenanthrone (3a) was achieved by a convergent approach, making use of a transition-metal-catalyzed domino process with an intramolecular Diels-Alder reaction at an isobenzopyrylium cation as key step.

Full text of DOI:10.1021/jo050400a

SCHEME 1. Cyclization to Model Phenanthrone 2
Total Synthesis of Heliophenanthrone
Gerald Dyker* and Dirk Hildebrandt
Fakulta¨t fu¨r Chemie, Ruhr-Universita¨t Bochum,
Universita¨tsstrasse 150, D-44780 Bochum, Germany
gerald.dyker@rub.de
Received March 3, 2005
The successful transformation of model compound 17
to phenanthrone 2 via an intramolecular Diels-Alder
reaction confirmed the applicability of this method for
the construction of the target framework (Scheme 1). In
analogy, our retrosynthetic analysis of heliophenanthrone
(3a) suggested the substituted acetophenone 5 and the
heptadiyne diastereoisomer 6a as building blocks for a
convergent total synthesis (Scheme 2).
Coupling component 5 is conveniently synthesized in
just one step from 3-bromotoluene following the proce-
dure of Yu et al.8 For the synthesis of bisalkyne 6a the
glyoxylate 7 was chosen as starting material (Scheme 3).
The first ethynyl group was introduced by a Reformatsky-
type reaction with an organozinc reagent generated in
situ.9 Supported by sonication, this reaction took less
than 5 min. After distillation of the crude product, the
pentynoic ester 8 was obtained in 67% yield. The three-
step sequence of methylation at the hydroxyl function,10
reduction of the ester with LiAlH4,11 and subsequent
Swern oxidation12 gave the corresponding aldehyde 10
The total synthesis of rac-heliophenanthrone (3a) was
achieved by a convergent approach, making use of a transi-
tion-metal-catalyzed domino process with an intramolecular
Diels-Alder reaction at an isobenzopyrylium cation as key
step.
Heliophenanthrone (3a) is a dihydrophenanthrene
derivative which was isolated from Heliotropium ovali-
folium by Hostettmann et al.1 This herbaceous plant is
infamous for its toxicity for cattle and sheep, but has also
delivered some lead compounds for antibacterial and
antifungal benzoquinones.2
We became interested in the synthesis of this natural
product during our studies on gold-catalyzed domino
processes.3 Gold and platinum salts as catalysts are a
focus of current interest: as rather soft and carbophilic
Lewis acids they have demonstrated high activity in
various reactions,4 such as in alkylations of arenes and
â-ketoesters, nucleophilic additions to alkenes and alkynes,
as well as in isomerizations of enynes.5 Gold, platinum,
and copper salts are known for inducing the cyclization
of o-alkynylbenzaldehydes and o-alkynylaryl ketones to
isobenzopyrylium salts, which are interesting reactive
intermediates for subsequent transformations, such as
cycloaddition processes to polycyclic ring systems.6 We
envisioned that the tricyclic heliophenanthrone (3a)
would be a suitable target for such a domino process.
(5) Current examples of gold catalyzed reactions: (a) Shi, Z.; He,
C. J. Am. Chem. Soc. 2004, 126, 5964. (b) Shi, Z.; He, C. J. Org. Chem.
2004, 69, 3669. (c) Luo, Y.; Li, C.-J. Chem. Commun. 2004, 1930. (d)
Shi, Z.; He, C. J. Am. Chem. Soc. 2004, 126, 13596. (e) Kennedy-Smith,
J. J.; Staben, S. T.; Toste, F. D. J. Am. Chem. Soc. 2004, 126, 4526. (f)
Staben, S. T.; Kennedy-Smith, J. J.; Toste, F. D. Angew. Chem. 2004,
116, 5464. Staben, S. T.; Kennedy-Smith, J. J.; Toste, F. D. Angew.
Chem., Int. Ed. 2004, 43, 5350. (g) Yao, X.; Li, C.-J. J. Am. Chem. Soc.
2004, 126, 6884. (h) Hashmi, A. S. K.; Ding, L.; Bats, J. W.; Fischer,
P.; Frey, W. Chem. Eur. J. 2003, 9, 4339. (i) Harrak, Y.; Blaszykowski,
C.; Bernard, M.; Cariou, K.; Mainetti, E.; Mouries, V.; Dhimane, A.-
L.; Fensterbank, L.; Malacria, M. J. Am. Chem. Soc. 2004, 126, 8656.
(j) Nieto-Oberhuber, C.; Mun˜oz, M. P.; Bun˜uel, E.; Nevado, C.;
Ca´rdenas, D. J.; Echavarren, A. M. Angew. Chem. 2004, 116, 2456.
Nieto-Oberhuber, C.; Mun˜oz, M. P.; Bun˜uel, E.; Nevado, C.; Ca´rdenas,
D. J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2004, 43, 2402. (k)
Luzung, M. R.; Markham, J. P.; Toste, F. D. J. Am. Chem. Soc. 2004,
126, 10858. (l) Mamane, V.; Gress, T.; Krause, H.; Fu¨rstner, A. J. Am.
Chem. Soc. 2004, 126, 8654. (m) Hashmi, A. S. K.; Ding, L.; Bats, J.
W.; Fischer, P.; Frey, W. Chem. Eur. J. 2003, 9, 4339. (n) Miki, K.;
Yokoi, T.; Nishino, F.; Kato, Y.; Washitake, Y.; Ohe, K.; Uemura, S. J.
Org. Chem. 2004, 69, 1557. (o) Yao, T.; Zhang, X.; Larock, R. C. J.
Am. Chem. Soc. 2004, 126, 11164.
(6) (a) Asao, N.; Aikawa, H.; Yamamoto, Y. J. Am. Chem. Soc. 2004,
126, 7458. (b) Zhu, J.; Germain, A. R.; Porco, J. A., Jr. Angew. Chem.
2004, 116, 1259. Zhu, J.; Germain, A. R.; Porco, J. A., Jr. Angew. Chem.,
Int. Ed. 2004, 43, 1239. (c) Asao, N.; Takahashi, K.; Lee, S.; Kasahara,
T.; Yamamoto, Y. J. Am. Chem. Soc. 2002, 124, 12650. (d) Dyker, G.;
Stirner, W.; Henkel, G.; Ko¨ckerling, M. Tetrahedron Lett. 1999, 40,
7457.
(7) Preparation of compound 1 is described in the Supporting
Information.
(8) Yu, C. J.; Chong, Y.; Kayyem, J. F.; Gozin, M. J. Org. Chem.
1999, 64, 2070.
(1) Guilet, D.; Guntern, A.; Ioset, J.-R.; Queiroz, E. F.; Ndjoko, K.;
Foggin, C. M.; Hostettmann, K. J. Nat. Prod. 2003, 66, 17.
(2) (a) Creeper, J. H.; Mitchell, A. A.; Jubb, T. F.; Colegate, S. M.
Aust. Vet. J. 1999, 77, 401. (b) Abu Damir, H.; Adam, S. E.; Tartour,
G. Br. Vet. J. 1982, 138, 463. (c) Mohanraj, S.; Kulanthaivel, P.;
Subramanian, P.; Herz, W. Phytochemistry 1981, 20, 1991.
(3) Dyker, G.; Hildebrandt, D.; Liu, J.; Merz, K. Angew. Chem. 2003,
115, 4536. Dyker, G.; Hildebrandt, D.; Liu, J.; Merz, K. Angew. Chem.,
Int. Ed. 2003, 42, 4399.
(4) For reviews on gold catalysis, see: (a) Dyker, G. Angew. Chem.
2000, 112, 4407. Dyker, G. Angew. Chem., Int. Ed. 2000, 39, 4237. (b)
Hashmi, A. S. K. Gold Bull. 2004, 37, 51. (c) Hoffmann-Ro¨der, A.;
Krause, N. Org. Biomol. Chem. 2005, 3, 387.
(9) (a) Bohlmann, F.; Herbst, P.; Gleinig, H. Chem. Ber. 1960, 94,
948. (b) Han, B.-H.; Boudjouk, P. J. Org. Chem. 1982, 47, 5030.
(10) Bales, B. C.; Horner, J. H.; Huang, X.; Newcomb, M.; Crich,
D.; Greenberg, M. M. J. Am. Chem. Soc. 2001, 123, 3623.
(11) (a) Colonge, J.; Gelin, R. Bull. Soc. Chim. Fr. 1954, 799. (b)
Stammler, R.; Halvorsen, K.; Gotteland, J.-P.; Malacria, M. Tetrahe-
dron Lett. 1994, 35, 417.
10.1021/jo050400a CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/24/2005
J. Org. Chem. 2005, 70, 6093-6096
6093

SCHEME 2. Retrosynthetic Analysis of Heliophenanthrone (3a)
SCHEME 3. Total Synthesis of Rac-Heliophenanthrone (3a)a
a Key: (a) Zn, Propargyl bromide, dioxane, sonication, 5 min; (b) NaH, MeI, THF; (c) (1) LiAlH4, THF, (2) Swern oxidation; (d) TMS-
acetylene, n-BuLi, THF; (e) (1) + aryl bromide 5, Sonogashira coupling reaction, (2) n-Bu4NF, THF; (f) TBDMSCl, imidazole, DMF; (g)
PtCl2, dioxane, 120 °C, 3 h; (h) HF, CH3CN, 2 h.
in acceptable overall yield. Finally, lithiated trimethyl-
silyl acetylene was classically added to the aldehyde
functionality.13 The resulting mixture of diastereoisomers
6a and 6b in the ratio 1:2.2 was directly coupled with
aryl bromide 5 in a Sonogashira reaction,14 followed by
the cleavage of the TMS group with n-Bu4NF solution in
THF:15 the mixture of diastereomeric ketones 4a and 4b
was obtained by flash chromatography in 50% yield. As
it turned out, the hydroxyl group had to be protected for
the gold-catalyzed step; otherwise, the reaction com-
pletely failed. Silylation with TBDMS chloride was
chosen for protection to give 12a/b in 90% yield.15 The
gold(III) chloride catalyzed cyclization of these dialkynyl
ketones to the TBDMS-protected heliophenanthrone 11a
and its diastereomer 11b gave only a moderate 35%
overall yield. By changing to platinum(II) chloride as
(12) Mancuso, A. J.; Huang, S.-L.; Swern, D. J. Org. Chem. 1978,
43, 2480.
(13) Chen, M.-J.; Lo, C.-Y.; Chin, C.-C.; Liu, R.-S. J. Org. Chem.
2000, 65, 6362.
(15) (a) Faure, S.; Piva-Le-Blanc, S.; Bertrand, C.; Pete, J.-P.; Faure,
R.; Piva, O. J. Org. Chem. 2002, 67, 1061. (b) Hanessian, S.; Lavalle´e,
P. Can. J. Chem. 1975, 53, 2975. (c) Morton, D. R.; Thompson, J. L. J.
Org. Chem. 1978, 43, 2102.
(14) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 4467. (b) Roesch, K. R.; Larock, R. C. J. Org. Chem. 2002, 67,
86.
6094 J. Org. Chem., Vol. 70, No. 15, 2005

SCHEME 4. Mechanistic Rationale
20 mL of CH2Cl2 was added dropwise within 5 min and the
mixture stirred an additional 15 min. A 16.0 mL (114 mmol)
portion of triethylamine was added, and after 5 min the reaction
was allowed to warm to room temperature. Water was added,
and the aqueous phase was extracted 3 times with CH2Cl2. The
organic extract was washed with brine and dried over sodium
sulfate. The solvent was removed by distillation under normal
pressure, and the aldehyde 10 was distilled under vacuum (∼30
mbar, 70 °C). The product 10 (1.57 g, 14.0 mmol, 61%) is a
colorless liquid. IR (NaCl): ν˜ ) 3289 (vs), 2993 (w), 2937 (s),
2832 (s), 2735 (w), 2121 (w), 1736 (vs), 1189 (s), 1115 (vs), 1042
catalyst in dioxane at 120 °C the overall yield of 11a/b
was raised to 71%. The mechanistic rationale (Scheme
4) for this domino process includes isobenzopyrylium
cation 13a and the Diels-Alder product 14a as reactive
intermediates.3,6,16
The two diastereoisomers 11a and 11b were easily
separated by flash chromatography, as anticipated with
the minor isomer 11a as the protected natural product.
Desilylation had to be performed under very mild condi-
tions to prevent dehydratization and subsequent aroma-
tization. With aqueous HF in acetonitrile17 this final step
in the synthesis of heliophenanthrone succeeded with
almost quantitative yield, and the spectroscopic data (1H
NMR, MS) of the product proved to be identical with
reported data.1
The transition-metal-catalyzed formation of isoben-
zopyrylium salts with a subsequent Diels-Alder reaction
was proven to be a very valuable method for the con-
struction of highly functionalized carbocyclic ring sys-
tems, with heliophenanthrone (3a) as a representative
example. A high degree of complexity is achieved in just
one preparative step, thus demonstrating the synthetic
potential of this domino process.18
1
(s) cm-1. H NMR (CDCl3, 400 MHz): δ ) 2.05 (t, J ) 2.5 Hz,
1H), 2.61 (m, 2H), 3.53 (s, 3H), 3.72 (td, J ) 6.0, 1.5 Hz, 1H),
9.71 (d, J ) 1.5 Hz, 1H); 13C NMR {1H} (CDCl3, 100 MHz): δ )
20.2 58.7, 71.1, 78.6, 83.2, 201.7. MS (70 eV, EI): m/z ) 112 [M+]
(0.6), 83 (100), 68 (18), 55 (15), 53 (32), 51 (13), 45 (13). Anal.
Calcd for C6H8O2 : C, 64.27; H, 7.16. Found: C, 64.63; H, 7.24.
4-Methoxy-1-trimethylsilanylhepta-1,6-diyn-3-ol (6a/b).
To a solution of 1.65 g (16.8 mmol) of trimethylsilylacetylene in
20 mL of THF was dropped 10.7 mL (16.9 mmol) of n-
butyllithium (1.6 M in hexane) at -78 °C. The mixture was
stirred for 1 h, and then 1.57 g (14 mmol) of 10 in 10 mL of
THF was added. The reaction was warmed to room temperature,
and 50 mL of water was added. The aqueous layer was extracted
three times with 20 mL portions of MTBE. The organic extract
was washed with brine and dried over sodium sulfate. The
solvents were evaporated, and the crude product was distilled
in a vacuum (1 mbar, 95-102 °C). The diastereoisomers 6a and
6b (1.71 g, 8.12 mmol, 58%) were obtained in the ratio 1/2.2 as
a colorless liquid. IR (NaCl): ν˜ ) 3431 (s), 3299 (s), 2959(s), 2900
Experimental Section
(s), 2832 (m), 2174 (m), 2122 (w), 1251 (s), 1114 (s), 1071 (s) cm-1
.
4-Oxo-3,4-dihydro-1H-phenanthrene-2,2-dicarboxylic
Acid Diethyl Ester (2). In a screw-capped flask, 170 mg (0.50
mmol) of 1 and 4.5 mg (15 µmol) of AuCl3 were dissolved in 10
mL of acetonitrile. The mixture was stirred at 80 °C for 3 h,
and after cooling to room temperature it was filtered through a
short silica pad (eluent: ethyl acetate). Evaporation of the
solvents and flash chromatography of the residue (SiO2, petro-
leum ether/MTBE (4:1) Rf ) 0.27) gave product 2 (160 mg, 0.47
mmol) in a yield of 94% as colorless crystals (mp 83 °C). IR
(KBr): ν˜ ) 3055 (m), 2988 (s), 2904 (m), 2877 (m), 1755 (vs),
1729 (vs), 1673 (s), 1594 (s), 1511 (s), 1442 (m), 1434 (s), 1384
(m), 1371 (s), 1330 (s), 1306 (vs), 1253 (vs), 1209 (vs), 1188 (vs),
1162 (s), 1151 (s), 1139 (s), 1125 (s), 1092 (m), 1078 (s), 1053 (s),
1H NMR (CDCl3, 400 MHz): δ ) 0.18 (s, 9H), 2.02 (“t”, 1H), 2.58
(m, 2H), 3.44-3.49 (m, 1H), 3.53 and 3.57 (s, 3H), 4.45 and 4.58
(d, J ) 5.0 and 4.5 Hz, 1H). 13C NMR {1H} (CDCl3, 100 MHz):
δ ) -0.09 and -0.06, 20.2 and 20.6, 59.0 and 59.4, 64.1 and
64.3, 70.2 and 70.6, 80.3 and 80.9, 82.0 and 82.2, 91.9, 102.8
and 103.7. MS (70 eV, EI): m/z ) 210 (M+, 0.4), 164 (5), 99 (10),
89 (10), 83 (100), 78 (7), 73 (73). Anal. Calcd for C11H18O2Si: C,
62.81; H, 8.63. Found: C, 62.60; H, 8.59.
1-[2-(5-Hydroxy-4-methoxyhepta-1,6-diynyl)-4-methylphen-
yl]ethanone (4a/b). In a screw-capped flask 480 mg (2.25 mmol)
of acetophenone 5, 521 mg (2.48 mmol) of dialkyne 6a and 6b,
47.0 mg (0.07 mmol, 3 mol %) of PdCl2(PPh3)2, and 6.00 mg (0.03
mmol, 1.5 mol %) of CuI were suspended in 20 mL of triethy-
lamine. The mixture was heated under stirring at 80 °C for 5 h.
The suspension was filtered through a short silica pad with ethyl
acetate as eluent. After evaporation of the solvents, the residue
was dissolved in 2 mL of THF. Five milliliters of a 1 M n-Bu4-
NF solution in THF was added, and the solution was stirred for
2.5 h at room temperature. Brine was added, and the aqueous
layer was extracted with MTBE. The organic extract was washed
with an aqueous 5% HCl solution and dried over sodium sulfate.
Evaporation of the solvents and flash chromatography of the
residue (SiO2, petroleum ether/ethyl acetate (2:1) Rf ) 0.26) gave
product 4a/b (304 mg, 1.13 mmol, 50%) as yellow oil. IR (NaCl):
ν˜ ) 3425 (vs, br), 3289 (vs), 2926 (m), 2831 (s), 2328 (m), 2227
(w), 2116 (w), 1677 (vs), 1600 (s), 1357 (s), 1280 (s), 1249 (s),
1039 (s), 1012 (s), 819 (s), 752 (s) cm-1 1H NMR (CDCl3, 400
.
MHz): δ ) 1.16 (t, J ) 7.0 Hz, 6H), 3.26 (s, 2H), 3.67 (s, 2H),
4.15 (q, J ) 7.0 Hz, 4H), 7.35 (d, J ) 8.0 Hz, 1H), 7.51 (td, J )
7.5, 1.0 Hz, 1H), 7.64 (td, J ) 7.8, 1.5 Hz, 1H), 7.81 (d, J ) 8.0
Hz, 1H), 7.97 (d, J ) 8.5 Hz, 1H), 9.44 (d, J ) 9.0 Hz, 1H). 13C
NMR {1H} (CDCl3, 100 MHz): δ ) 14.2 36.9, 45.4, 55.1, 62.2,
126.37, 126.42, 126.88, 126.92, 128.5, 129.4, 131.3, 133.3, 135.4,
142.2, 169.9, 195.6. MS (70 eV, EI): m/z ) 340 [M+] (48), 295
(7), 267 (100), 239 (16), 221 (16), 195 (52), 177 (14), 165 (46),
140 (12). Anal. Calcd for C20H20O5: C, 70.57; H, 5.92. Found:
C, 70.19; H, 5.73.
2-Methoxypent-4-ynal (10). In a 250 mL, three-neck flask
equipped with a mechanical stirrer and two dropping funnels
was added with stirring a mixture of 2.30 mL (25.1 mmol) of
oxalyl chloride and 60 mL of CH2Cl2 at -70 °C. A 3.90 mL (50.2
mmol) portion of DMSO in 10 mL of CH2Cl2 was added dropwise.
After 2 min, 2.60 g (22.8 mmol) of 2-methoxy-pent-4-yn-1-ol in
1112 (s), 1064 (s) cm-1 1H NMR (CDCl3, 400 MHz): δ ) 2.35
.
(s, 3H), 2.52 (“t”, 1H), 2.67 (s, 3H), 2.76-2.96 (“dd” and “dd”,
2H), 3.49-3.65 (m, 1H), 3.57 and 3.59 (s, 3H), 4.61 and 4.71 (dd,
J ) 4.8, 2.0 Hz and 4.3, 2.0 Hz, 1H), 7.16 (d, J ) 8.0 Hz, 1H),
7.32 (s, 1H), 7.63 (d, J ) 8.0 Hz, 1H). 13C NMR {1H} (CDCl3,
100 MHz): δ ) 21.3 21.4 and 21.5, 29.6 and 29.7, 58.9 and 59.1,
63.9 and 64.0, 74.4 and 74.7, 81.6, 82.0 and 82.1, 82.2, 91.0 and
91.1, 122.09 and 122.13, 128.90 and 128.92, 129.20 and 129.24,
(16) Straub, B. F. Chem. Commun. 2004, 1726.
(17) Newton, R. F.; Reynolds, D. P. Tetrahedron Lett. 1979, 41, 3981.
(18) Tietze, L. F.; Beifuss, U. Angew. Chem. 1993, 105, 137. Tietze,
L. F.; Beifuss, U. Angew. Chem., Int. Ed. Engl. 1993, 32, 131.
J. Org. Chem, Vol. 70, No. 15, 2005 6095

135.0 and 135.1, 137.89 and 137.93, 142.1, 199.7. MS (70 eV,
EI): m/z ) 269 [M+] (0.8), 255 (6), 221 (10), 215 (40), 196 (100),
185 (18), 172 (44), 146 (13), 128 (36), 115 (15). Anal. Calcd
C17H18O3 : C, 75.53; H, 6.71. Found: C, 75.46; H, 6.70.
1H), 7.90 (d, J ) 8.6 Hz, 1H), 9.25 (s, 1H).; 13C NMR {1H} (CDCl3,
100 MHz): δ ) -4.3, -4.1, 18.4, 20.5, 22.3, 26.1, 42.2, 57.0, 72.7,
80.5, 124.0, 124.8, 126.1, 126.7, 128.5, 131.0, 131.3, 138.7, 142.0,
144.6, 197.7. MS (70 eV, EI): m/z ) 384 [M+] (1.5), 327 (100),
295 (9), 209 (5), 179 (5), 149 (5). 11b. IR (KBr): ν˜ ) 2928 (s),
2854 (s), 1664 (vs), 1140 (s), 1112 (s), 1075 (s), 986 (s), 838 (vs),
1-{2-[5-(tert-Butyldimethylsilanyloxy)-4-methoxyhepta-
1,6-diynyl]-4-methyl-phenyl}ethanone (12a/b). To a solution
of 288 mg (1.07 mmol) of 4a/b in 10 mL of DMF 241 mg (1.60
mmol) of tert-butyldimethylsilyl chloride and 254 mg (3.73 mmol)
of imidazole were successively added. After being stirred over-
night, the mixture was diluted with 20 mL of brine and extracted
with MTBE (5 × 10 mL). The organic layer was washed with a
cooled aqueous 5% HCl solution and with brine and dried over
sodium sulfate. Evaporation of the solvents and flash chroma-
tography of the residue (SiO2, petroleum ether/ethyl acetate (10:
1) Rf ) 0.16) gave product 12a/b (369 mg, 0.96 mmol, 90%) as
yellow oil. IR (NaCl): ν˜ ) 3305 (s), 2953 (vs), 2928 (vs), 2889
(s), 2856 (vs), 2229 (w), 2115 (w), 1680 (vs), 1602 (s), 1358 (s),
1278 (s), 1253 (vs), 1118 (vs), 838 (vs), 781 (vs), 671 (s) cm-1. 1H
NMR (CDCl3, 400 MHz): δ ) 0.14 and 0.15 (s, 3H), 0.17 (s, 3H),
0.92 and 0.93 (s, 9H), 2.34 (s, 3H), 2.45 (“t”, 1H), 2.71 and 2.72
(s, 3H), 2.74-2.94 (m, 2H), 3.46-3.54 (m, 1H), 3.56 and 3.58 (s,
3H), 4.58-4.59 (“dd”, 1H), 7.14 (d, J ) 8.0 Hz, 1H), 7.31 (s, 1H),
7.62 (d, J ) 8.0 Hz, 1H). 13C NMR {1H} (CDCl3, 100 MHz): δ )
-5.0, -4.9, -4.6 , -4.5, 18.3 and 18.4, 21.3, 21.8 and 21.9, 25.9,
30.1 and 30.2, 59.3 and 59.6, 64.5 and 64.7, 73.8 and 74.4, 81.1
and 81.5, 82.5 and 82.9, 83.0 and 83.2, 92.7 and 93.3, 122.4,
128.8, 128.9, 134.8, 138.3, 141.9, 200.2 and 200.3. MS (70 eV,
EI): m/z ) 384 [M+] (2), 353 (8), 327 (43), 295 (5), 215 (25), 196
(41), 185 (7), 171 (50), 157 (5), 141 (5), 128 (16), 115 (8), 89 (100).
HRMS (ESI) calcd for C23H33O3Si (M+ + H) 385.2193, found
385.2205.
1
776 (s), 676 (m) cm-1. H NMR (CDCl3, 400 MHz): δ ) 0.10 (s,
3H), 0.21 (s, 3H), 0.90 (s, 9H), 2.56 (s, 3H), 2.73 (s, 3H), 2.87
and 3.17 (dd and dd, J ) 17.0, 4.5 Hz and 17.0, 8.5 Hz, 2H),
3.45 (s, 3H), 3.86 (ddd, J ) 8.5, 4.5, 2.5 Hz, 1H), 5.09 (d, J ) 2.5
Hz, 1H), 7.35 (s, 1H), 7.39 (dd, J ) 8.8, 1.5 Hz, 1H), 7.91 (d, J )
8.5 Hz, 1H), 9.25 (s, 1H).; 13C NMR {1H} (CDCl3, 100 MHz): δ )
-4.4, -4.2, 18.5, 20.5, 22.3, 25.9, 41.6, 56.9, 71.6, 78.5, 124.1,
124.9, 125.8, 126.5, 128.5, 131.1, 131.4, 139.8, 142.1, 144.4, 198.3.
MS (70 eV, EI): m/z ) 384 [M+] (1), 327 (65), 221 (6), 179 (5),
89 (100). Anal. Calcd C23H32O3Si: C, 71.83; H, 8.39. Found: C,
71.68; H, 8.51.
rac-Heliophenanthrone (3a). In a 25 mL flask,30 mg (77
µm) of 11a was dissolved in 2 mL of 5% of a 40% aqueous
solution of HF in acetonitrile. After 2 h of stirring at room
temperature, 10 mL of chloroform and 10 mL of water were
added. The organic phase was removed, and the aqueous layer
was extracted once again with 10 mL of chloroform. Evaporation
of the solvents and flash chromatography of the residue (SiO2,
petroleum ether/ethyl acetate (1:2) Rf ) 0.23) gave product 3a
(21 mg, 73 µm, 93%) as colorless crystals (mp 157-158 °C). IR
(KBr): ν˜ ) 3330 (br, s), 2924 (s), 1662 (vs), 1595 (s), 1243 (m),
1177 (m), 1145 (m), 1113 (s), 1079 (m), 1051 (m), 833 (m), 815
(m), 750 (m) cm-1. 1H NMR (CDCl3, 400 MHz): δ ) 2.57 (s, 3H),
2.65 and 3.31 (dd and dd, J ) 16.3, 10.6 Hz and 16.3, 4.5 Hz,
2H), 2.76 (s, 3H), 3.52 (s, 3H), 3.71 (ddd, J ) 10.6, 8.5, 4.5 Hz,
1H), 4.91 (d, J ) 8.5 Hz, 1H), 7.41 (dd, J ) 8.5, 1.5 Hz, 1H),
7.70 (s, 1H), 7.93 (d, J ) 8.5 Hz, 1H), 9.28 (s, 1H). 13C NMR
{1H} (CDCl3, 100 MHz): δ ) 20.6, 22.4, 43.3, 57.0, 72.7, 80.7,
123.6, 123.7, 124.2, 126.4, 128.7, 130.9, 131.2, 139.1, 143.0, 144.2,
196.9.; MS (70 eV, EI): m/z ) 270 [M+] (51), 212 (100), 184 (36),
169 (17), 155 (23), 141 (8), 128 (5), 115 (5).
1-(tert-Butyldimethylsilanyloxy)-2-methoxy-6,9-dimeth-
yl-2,3-dihydro-1H-phenanthren-4-one (11a) and (11b). In
a screw-capped flask 107 mg (0.28 mmol) of 12a/b and 4.0 mg
(14 µmol) of PtCl2 were dissolved in 20 mL of dioxane. The
mixture was stirred at 120 °C for 3 h, and after being cooled to
room temperature it was filtered through a short silica pad
(eluent: ethyl acetate). Evaporation of the solvents and flash
chromatography of the residue (SiO2, petroleum ether/ethyl
acetate (16:1), Rf ) 0.30, 0.23) gave product 11a (fraction 1, 27.0
mg, 0.07 mmol, 25%) and product 11b (fraction 2, 49.0 mg 0.13
mmol, 46%) in an overall yield of 71% as yellow resin (11a, mp
104-105 °C; 11b, mp 89-90 °C). 11a. IR (KBr): ν˜ ) 2962 (s),
2927 (s), 2895 (s), 2855 (s), 1663 (s), 1259 (s), 1242 (s), 1142 (s),
Acknowledgment. We gratefully acknowledge fi-
nancial support from the Deutsche Forschungsgemein-
schaft (DFG) and the Fonds der Chemischen Industrie.
We offer special thanks to Werner Karow from the
University of Essen for measuring the HRMS spectra.
1
1106 (s), 1095 (s), 778 (m), 676 (w) cm-1. H NMR (CDCl3, 400
Supporting Information Available: Characterization
data and spectra of all products. This material is available free
of charge via the Internet at http://pubs.acs.org.
MHz): δ ) 0.15 (s, 3H), 0.23 (s, 3H), 0.94 (s, 9H), 2.55 (s, 3H),
2.72 (s, 3H), 2.77 and 3.29 (dd and dd, J ) 16.6, 7.0 Hz and
16.6, 4.0 Hz, 2H), 3.42 (s, 3H), 3.78 (“ddd”, J ) 6.5, 4.0 Hz, 1H),
4.90 (d, J ) 6.0 Hz, 1H), 7.39 (dd, J ) 8.5, 1.5 Hz, 1H), 7.41 (s,
JO050400A
6096 J. Org. Chem., Vol. 70, No. 15, 2005