Full text of DOI:10.1016/S0040-4039(00)00682-1

Tetrahedron Letters 41 (2000) 4545±4547
Regioselective synthesis of functionalized homophthalates by
cyclizations of 1,3-bis-(trimethylsiloxy)-1,3-butadienes with
a-allenylesters
Peter Langer* and Bettina Kracke
Institut fur Organische Chemie der Georg-August-Universitat Gottingen, Tammannstr. 2, D-37077 Gottingen, Germany
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Received 6 March 2000; accepted 25 April 2000
Abstract
Reaction of 1,3-bis-(trimethylsiloxy)-1,3-butadienes with a-allenylesters resulted in regioselective formation
of functionalized homophthalates which represent useful building blocks for natural product syntheses.
# 2000 Elsevier Science Ltd. All rights reserved.
Despite numerous reports of cycloaddition reactions of alkynes there is a relative paucity of
work on the use of allenes as dienophiles in Diels±Alder reactions.1 This is presumably due to
the instability of many allenes under the increased temperatures required for cycloaddition reactions.
In the course of our interest in cyclization reactions of dianion synthons we have recently reported2
cyclizations of 1,3-bis-(trimethylsiloxy)-1,3-butadienes, synthons of 1,3-dicarbonyl dianions,3
with oxalic acid dielectrophiles to give g-alkylidenebutenolides. Herein, we wish to report, to the
best of our knowledge, the ®rst cycloaddition reactions of allenes with 1,3-bis-(trimethylsiloxy)-
1,3-butadienes.4 These reactions provide a convenient and regioselective access to a variety of
functionalized homophthalates which are of interest as building blocks in the synthesis of natural
products.4
Our ®rst attempts to induce a cyclization reaction of dimethyl allenedicarboxylate 25 with 1,3-
bis-(trimethylsiloxy)-1,3-diene 1a were unsuccessful: when the reaction was carried out in toluene,
no conversion was observed at 20ꢀC. In contrast, at elevated temperatures, decomposition was
observed. Equally disappointing results were observed, when the reaction was carried out in
CH2Cl2 in the presence of Lewis acids. In contrast, a clean cyclization could be induced when the
neat starting materials were stirred at 20ꢀC for 1 h to give homophthalate 3a.4,6 Optimal yields
(up to 75%) were obtained for 3a when the reaction mixture was worked up using triethyl
ammonium ¯uoride7 in 95% ethanol. Formation of 3a can be explained by regioselective cyclization
* Corresponding author. Fax: +551 399475; e-mail: planger@gwdg.de
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00682-1

4546
and subsequent aromatization by ¯uoride-induced cleavage of the trimethylsilyl groups and
elimination of ethanol (Table 1).
Table 1
In order to study the preparative scope of the cyclization reaction the substituents of the 1,3-
bis-(trimethylsiloxy)-1,3-butadienes were systematically varied. Reaction of allene 2 with 1,3-bis-
(trimethylsiloxy)-1,3-dienes 1b±f, containing a methyl-, ethyl-, butyl-, benzyl-, and allyl group at
the terminal carbon atom, a€orded the homophthalates 3b±f in good yields and with very good
regioselectivities. Reaction of 2 with 4-methoxy-1,3-bis-(trimethylsiloxy)-1,3-diene 1g a€orded the
highly functionalized homophthalate 3g. Starting with the 1,3-bis-(trimethylsiloxy)-1,3-diene 1h,
containing a methyl group at the central carbon atom, the homophthalate 3h was isolated (Table 2).
Table 2
Reaction of allene 2 with the diketone derived 1,3-bis-(trimethylsiloxy)-1,3-dienes 1i±l resulted
in regioselective cyclization and elimination of water upon treatment with HNEt3F to give the
homophthalates 3i±l. These products contain an alkyl or an aryl group (R3) rather than a
hydroxy group at carbon C-5. Starting with the dienes derived from acetylacetone, 2-methyl-
acetylacetone, methyl 2-acetyl-acetoacetate and benzoylacetone, the homophthalates 3i±l were
prepared in good yields.

4547
Acknowledgements
P.L. thanks Professor A. de Meijere for his support. Financial support from the Fonds der
Chemischen Industrie (Liebig-scholarship and funds for P.L.) and the Deutsche Forschungs-
gemeinschaft is gratefully acknowledged.
References
1. (a) De Schrijver, J.; De Clerq, P. J. Tetrahedron Lett. 1993, 34, 4369; (b) Spitzner, D.; Klein, I. Liebigs Ann. Chem.
1990, 63; (c) Gibbs, R. A.; Bartels, K.; Lee, R. W. K.; Okamura, W. H. J. Am. Chem. Soc. 1989, 111, 3717; (d)
Reich, H. J.; Eisenhart, E. K.; Olson, R. E.; Kelly, M. J. J. Am. Chem. Soc. 1986, 108, 7791; (e) Hayakawa, K.;
Nishiyama, H.; Kanematsu, K. J. Org. Chem. 1985, 50, 512; (f) Fink, M.; Gaier, H.; Gerlach, H. Helv. Chim. Acta
1982, 65, 2563; (g) Danishefsky, S.; Singh, R. K.; Gammill, R. B. J. Org. Chem. 1978, 43, 379; (h) Kozikowski,
A. P.; Floyd, W. C.; Kuniak, M. P. J. Chem. Soc., Chem. Commun. 1977, 582; (i) Banville, J.; Brassard, P. J. Chem.
Soc., Perkin Trans. 1 1976, 1852.
2. (a) Langer, P.; Stoll, M. Angew. Chem. 1999, 111, 1919; Angew. Chem., Int. Ed. 1999, 38, 1803; (b) Langer, P.;
Schneider, T.; Stoll, M. Chem. Eur. J. 2000, in press; (c) Langer, P.; Holtz, E. Angew. Chem. 2000, accepted for
publication.
3. (a) Chan, T.-H.; Brownbridge, P. J. Am. Chem. Soc. 1980, 102, 3534; (b) Molander, G. A.; Cameron, K. O. J. Am.
Chem. Soc. 1993, 115, 830.
4. Homophthalate 3a has been previously prepared and used for the synthesis of a naphthoate precursor to olivin,
see: Roush, W. R.; Murphy, M. J. Org. Chem. 1992, 57, 6622.
5. Bryson, T. A.; Dolak, T. M. Org. Synth. 1977, 57, 62.
6. Procedure for the preparation of homophthalate 3a: To neat allene 2 (0.315 ml, 1.2 mmol) was added neat diene
1a (410 mg, 1.5 mmol) at 0ꢀC under nitrogen. The reaction mixture was stirred at 20ꢀC for 1 h. The solution was
then treated with a solution of triethylammonium ¯uoride (230 mg, 1.8 mmol) in 96% ethanol (2 ml). The solution
was diluted with water and repeatedly extracted with ether. The combined organic extracts were dried (MgSO4),
®ltered and the solvent of the ®ltrate was removed in vacuo. The residue was puri®ed by column chromatography
(silica gel, ether/petrol ether=1:1) to give 3a as a colorless solid (215 mg, 75%): 1H NMR (MeOH-d4, 200 MHz):
3.70, 3.81 (s, 2Â3H, CH3), 3.82 (s, 2H, CH2), 6.23, 6.25 (2Âd, 3 Hz, 2Â1H, CH). 13C NMR (MeOH-d4, 50 MHz):
43.26, 52.10, 52.38, 103.07, 105.05, 114.19, 140.01, 164.24, 166.43, 172.36, 174.19. MS (70 eV, m/z): 240 (M+, 20).
Anal. calcd for C11H12O6: C, 55.00; H, 5.04. Found: C, 55.25; H, 4.92. All new compounds gave satisfactory
spectroscopic and analytical and/or high resolution mass data.
7. Hung, S.; Wehner, G. Synthesis 1975, 180.