Rhodium-catalyzed synthesis of cyclohexenones via a novel [4 + 2] annulation

Organic Letters

Volumn 4, Issue 6, 2002, Pages 933-935

  Tanaka, Ken ^a   Fu, Gregory C ^a  

^a MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

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EID: 0010224792     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol017308v     Document Type: Article

References (14)

1. Tanaka, K.; Fu, G. C. Submitted for publication.
2. (a) For a review of transition metal-catalyzed carbocyclizations, see: Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem. Rev. 1996, 96, 635-662.
3. (b) For a review of transition metal-mediated cycloaddition reactions, see: Lautens, M.; Klute, W.; Tam W. Chem. Rev. 1996, 96, 49-92
4. (c) For a review of transition metal-mediated cycloaddition reactions of alkynes, see: Schore, N. E. Chem. Rev. 1988, 88, 1081-1119.
5. For a recent example of a rhodium-catalyzed intermolecular cycloaddition process that involves an alkyne, see: Wender, P. A.; Barzilay, C. M.; Dyckman, A. J. J. Am. Chem. Soc. 2001, 123, 179-180.
6. For the synthesis of quinones via the reaction of maleoylcobalt complexes with alkynes, see: Iyer, S.; Liebeskind, L. S. J. Am. Chem. Soc. 1987, 109, 2759-2770, and references therein.
7. 2 (2.0 mL) was added by pipet. The Schlenk tube was closed, and the mixture was stirred at room temperature for 24 h. The solution was then concentrated and purified by preparative TLC (hexanes:EtOAc = 10:1). which furnished (E)-6-heptylidene-5-methyl-3-oxo-2-phenylcyclohex-1-enecarboxylic acid ethyl ester (65.2 mg. 0.184 mmol. 66%) and (E)-3-heptylidene-4-methyl-6-oxo-2-phenylcyclohex-1-enecarboxylic acid ethyl ester (9.3 mg. 0.026 mmol, 10%).
8. (a) For all of these annulations, the regioisomers have been separated by chromatography. (b) Use of a large excess of the alkyne leads to a very slow reaction.
9. 4 in the absence of a second alkyne, self-coupling to generate a cyclohexenone proceeds in 80% yield (1.7:1 mixture of regioisomers).
10. 1H NMR.
11. In Scheme 1, for the sake of simplicity, the elementary steps are drawn as irreversible.
12. For mechanistic studies of the rhodium-catalyzed cyclization of 4-alkenals to cyclopentanones, see: (a) Campbell, R. E., Jr.; Miller, R. G. J. Organomet. Chem. 1980, 186, C27-C31. Campbell, R. E., Jr.; Lochow, C. F.; Vora, K. P.; Miller, R. G. J. Am. Chem. Soc. 1980, 102, 5824-5830.
13. For mechanistic studies of the rhodium-catalyzed cyclization of 4-alkenals to cyclopentanones, see: (a) Campbell, R. E., Jr.; Miller, R. G. J. Organomet. Chem. 1980, 186, C27-C31. Campbell, R. E., Jr.; Lochow, C. F.; Vora, K. P.; Miller, R. G. J. Am. Chem. Soc. 1980, 102, 5824-5830.
14. (b) Fairlie, D. P.; Bosnich, B. Organometallics 1988, 7, 946-954.