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LETTER
Products; Thieme: Stuttgart, 2000, 608. (e) Krause, S.;
Schmalz, H.-G. In Organic Synthesis Highlights, IV; Wiley-
VCH: Weinheim, 2000, 212. (f) Posner, G. H.; Kahraman,
M. Eur. J. Org. Chem. 2003, 3889. (g) Habermehl, G.;
Hammann, P. E.; Krebs, H. C. Naturstoffchemie; Springer:
Berlin, 2002, 49. (h) Recently, a new method for the
construction of steroids was reported: Sünnemann, H. W.; de
Meijere, A. Angew. Chem. 2004, 116, 913; Angew. Chem.
Int. Ed. 2004, 43, 895. (i) For the use of the D→ABCD
approach in the synthesis of steroids see also: Vollhardt, K.
P. C. Pure Appl. Chem. 1985, 57, 1819. (j) Petit, M.;
Aubert, C.; Malacria, M. Org. Lett. 2004, 6, 3937.
Torr). The residue was dissolved in degassed Et2O–pentane
(1:4, 10 mL) and filtered through celite under an argon
atmosphere. FeCl3·H2O (0.49 g, 1.8 mmol) was dissolved in
MeCN (20 mL), pentane (20 mL) was added and the mixture
cooled to –20 °C. At this temperature the filtrate was added
under stirring, and stirring was continued for 30 min. The
reaction mixture was cooled to –60 °C and the pentane layer
was removed from the frozen MeCN layer. The MeCN layer
was allowed to warm to –20 °C, pentane (15 mL) was added,
and the above procedure was repeated four times. The
pentane layers were combined, the solvent was removed in
vacuo (30 °C/18 Torr), and the residue purified by
(5) Groth, U.; Huhn, T.; Richter, N. Liebigs Ann. Chem. 1993,
49.
chromatography on silica gel (Et2O–pentane, 1:1) to afford
steroids 15 (66.65 mg, 0.18 mmol, 33%).
(6) (a) Haruta, R.; Ishiguro, M.; Ikeda, N.; Yamamoto, H. J. Am.
Chem. Soc. 1982, 104, 7667. (b) Ikeda, N.; Isao, A.;
Yamamoto, H. J. Am. Chem. Soc. 1986, 108, 483.
(7) Pereira, R.; Iglesias, B.; Lera, A. R. Tetrahedron 2001, 57,
7871.
(8) Baldwin, J. E.; Romeril, S. P.; Lee, V.; Claridge, T. D. W.
Org. Lett. 2001, 3, 1145.
(9) Franck, X.; Araujo, M. E. V.; Julian, J.-C.; Hocquemiller,
R.; Figadère, B. Tetrahedron Lett. 2001, 42, 2801.
(10) Eckenberg, P.; Groth, U.; Huhn, T.; Richter, N.; Schmeck,
C. Tetrahedron 1993, 49, 1619.
(11) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 36, 3769.
(12) Cobalt-mediated [2+2+2] cycloaddition: A solution of
enediyne 14 (200 mg, 0.54 mmol) in toluene (80 mL) was
cooled to –70 °C and the apparatus was evacuated for 3 min
(0.5 Torr). The flask was allowed to warm to r.t. and the
apparatus was filled with argon. The solution of enediyne in
toluene was cooled to –70 °C and the above procedure was
repeated twice. CpCo(CO)2 (117 mg, 0.65 mmol) was added
and the reaction mixture was refluxed under radiation with
visible light until no starting material could be detected by
TLC analysis. The reaction mixture was cooled to r.t. and
volatile components were removed in vacuo (20 °C/0.1
Compound 15a/15¢a (signals of the major diastereomeric
pair): Rf = 0.27 (Et2O–PE, 1:1). 1H NMR (250 MHz,
CDCl3): d = 0.76 and 0.84 (2 s, 6 H, 2 × CH3), 1.20–2.80 (m,
16 H, CH2, CH), 3.40 (s, 3 H, OCH3), 3.50–3.64 and 3.66–
3.79 (2 × m, 5 H, OCH2CH2O, OCH), 4.78 (dd, J = 6 Hz,
6 Hz, 2 H, OCH2O), 5.47–5.68 (m, 2 H, C=CHC=CH).
13C NMR (50.3 MHz, CDCl3): d = 13.66 and 13.81 (C-18),
18.05, 18.38, 20.20, 20.23, 26.17, 28.80, 29.06, 33.96,
35.78, 35.85, 35.93, 36.12, 37.08, 38.03, and 38.28 (C-1, C-
2, C-4, C-10, C-11, C-12, C-15, C-16), 20.30 (C-19), 46.27
and 46.58 (C-9), 46.77 (C-13), 59.04 (C-23), 66.78 and
71.79 (C-21, C-22), 70.74 and 75.81 (C-3), 93.35 and 93.73
(C-20), 116.50, 116.57, 119.66 and 119.99 (C-6, C-7),
137.46, 137.94, 140.82 and 142.15 (C-5, C-8), 220.97 and
221.15 (C-17). MS (70 eV): m/z (%) = 374 (2) [M+], 268
+
(100) [M – C4H10O3]+, 89 (35) [C4H10O3 ], 59 (60)
[C3H7O+]. HRMS: m/z calcd C23H34O4 for 374.2457; found:
374. 2459.
(13) Purchased from Aldrich.
(14) (a) Confalone, P. N.; Kulesha, I. D.; Uskoković, M. R. J.
Org. Chem. 1981, 46, 1030. (b) Okabe, M.; Sun, R.-C.;
Scalone, M.; Jibilian, C. H.; Hutchings, S. D. J. Org. Chem.
1995, 60, 767.
Synlett 2006, No. 6, 905–908 © Thieme Stuttgart · New York