of an organolithium (4) or free radical (5) intermediate. While
we recognized that steric and conformational considerations
might work against the desired transformation, the ready
availability of cyclization substrate 2 in one step from 8-iodo-
1-naphthaldehyde6 made this an appealing route for our initial
studies. In the event, however, we were unable to effect the
desired transformation under any of a variety of conditions,
obtaining from each experiment either unreacted 2, or a
complex mixture of uncharacterizable products.
transformed to 8 by addition of the corresponding naphth-
yllithium species to acrolein followed by desilylation. The
key intramolecular Pauson-Khand reaction11 then proceeded
in good yield to furnish the desired cyclopentenone 9 as an
87:13 mixture of isomers in which the C-7 hydroxyl is cis
to the adjacent ring junction hydrogen in the major product.
Reduction of 9 was accomplished smoothly and with high
stereoselectivity using Li(s-Bu3)BH to furnish diol 10 (87:
13 ratio at C-7), which was also converted to the corre-
sponding diacetate (11) using standard acetylation conditions.
Unfortunately, all attempts to achieve the transformation
of these intermediates to cyclopenta[a]phenalene proved
unsuccessful. No cyclopenta[a]phenalene could be detected
among the products of either stepwise or “double elimina-
tion” reactions of diol 10 or its derivatives under a wide
variety of conditions, and attempts to effect the desired
elimination via flash vacuum pyrolysis of diacetate 11
(trapping of products at -198 °C) also proved fruitless.
Surmising now that cyclopenta[a]phenalene might in fact be
less stable than prior theoretical studies had suggested, we
turned our attention to the application of cyclopentenone 9
in the synthesis of substituted cyclopenta[a]phenalenes that
we anticipated might exhibit greater stability than the parent
compound.
We next turned our attention to a less direct route to
cyclopenta[a]phenalene in which a tetrahydro derivative
would first be constructed and then the requisite additional
unsaturation introduced in a stepwise fashion under carefully
controlled conditions. In this approach an intramolecular
Pauson-Khand reaction7 serves as the key step for the
assembly of the cyclopenta[a]phenalene carbon skeleton.
Synthesis of the Pauson-Khand substrate 8 proceeded
smoothly as outlined in Scheme 2. Thus, Sonogashira
Scheme 2
Scheme 3 outlines the results of this study, which
eventuated in the first syntheses of simple alkyl- and aryl-
Scheme 3
a Key: (a) 1.2 equiv of Me3SiCtCH, 0.04 equiv of Pd(PPh3)2Cl2,
0.08 equiv of CuI, Et3N, 16 h, 50-65%; (b) 1.1 equiv of n-BuLi,
Et2O, -30 °C, 15 min; then 2.0 equiv of acrolein, -78 °C, 1 h,
77-83%; (c) 0.1 equiv of K2CO3, MeOH, 2 h, 86-94%; (d) 1.1
equiv of Co2(CO)8, CH2Cl2; then 8.0 equiv of NMO, 4 h, 69-
73%; (e) 1.1 equiv of Li(s-Bu3)BH, THF, -78 °C, 15 min, 77-
80%; (f) 20 equiv of Ac2O, cat. DMAP, pyridine, 5 h, 76%.
substituted cyclopenta[a]phenalenes. The preparation of
9-phenylcyclopenta[a]phenalene was examined first. Addi-
tion of phenyllithium to cyclopentenone 9 proceeded poorly,
(5) Becker, D. A.; Danheiser, R. L. J. Am. Chem. Soc. 1989, 111, 389.
(6) Bailey, R. J.; Card, P. J.; Shechter, H. J. Am. Chem. Soc. 1983, 105,
6096.
(7) Schore, N. E. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Kidlington, 1995;
Vol. 12, pp 703-739.
(8) Sonogashira, K. In Metal-catalyzed Cross-Coupling Reactions;
Diederich, F., Stang, P. J., Eds.; Wiley-VCH: New York, 1998; pp 203-
230.
(9) Diiodide 6 was prepared in one step from the corresponding
commercially available diamine by the procedure of House et al.: House,
H. O.; Koepsell, D. G.; Campbell, W. J. J. Org. Chem. 1972, 37, 1003.
(10) For previous routes to this compound, see: (a) Feldman, K. S.;
Ruckle, R. E., Jr.; Ensel, S. M.; Weinreb, P. H. Tetrahedron Lett. 1992,
33, 7101. (b) Cobas, A.; Guitia´n, E.; Castedo, L. J. Org. Chem. 1997, 62,
4896.
coupling8 of trimethylsilylacetylene with 1,8-diiodonaphtha-
lene9 afforded the known naphthyl iodide 7,10 which was
(2) (a) Zahradnik, R.; Michl, J.; Koutechy, J. Collect. Czech. Chem.
Commun. 1964, 29, 1932. (b) Zahradnik, R.; Michl, J. Collect. Czech. Chem.
Commun. 1965, 30, 520. (c) Andes Hess, B., Jr.; Schaad, L. J. J. Org. Chem.
1971, 36, 3418. (d) Aihara, J. Bull. Chem. Soc. Jpn. 1980, 53, 2689. (e)
Zhou, Z.; Parr, R. G. J. Am. Chem. Soc. 1989, 111, 7371. (f) Ghosh, G.;
Ghosh, D.; Das Gupta, N. K. Bull. Chem. Soc. Jpn. 1991, 64, 3109.
(3) (a) Aitken, I. M.; Reid, D. H. J. Chem. Soc. 1956, 3487. (b) Kemp,
W.; Storie, I. T.; Tulloch, C. D. J. Chem. Soc., Perkin Trans. 1 1980, 2812.
(c) Blum, J.; Baidosi, W.; Badrieh, Y.; Hoffman, R. E. J. Org. Chem. 1995,
60, 4738 and references therein.
(4) (a) Sugihara, Y.; Fujita, H.; Murata, I. J. Chem. Soc., Chem. Commun.
1986, 1130. (b) Sugihara, Y.; Hashimoto, R.; Fujita, H.; Abe, N.; Yamamoto,
H.; Sugimura, T.; Murata, I. J. Chem. Soc., Perkin Trans. 1 1995, 2813.
(11) Best results were obtained using the general procedure of Shambayati
et al.: Shambayati, S.; Crowe, W. E.; Schreiber, S. L. Tetrahedron Lett.
1990, 31, 5289.
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Org. Lett., Vol. 2, No. 15, 2000