[2175-91-9]  · C8H10  · 6,6-Dimethylfulvene  · (MW 106.18)

(hydroazulene synthesis;2 alkene protection3)

Physical Data: bp 40-43 °C/8 mmHg.4

Form Supplied in: liquid; commercially available.

Preparative Method: by reaction of cyclopentadiene with acetone under basic conditions.4-7 The condensation has also been accomplished using pyrrolidine.8

Purification: distillation; chromatography on silica gel.

Handling, Storage, and Precautions: reported to undergo autoxidation to form an insoluble peroxide (C8H10O4) which explodes upon heating to 130 °C. Mixing the peroxide with ether in a mortar has resulted in ignition.9 Addition of hydroquinone is reported to suppress formation of this peroxide.10 Sensitized photooxygenation of 6,6-dimethylfulvene at -70 °C yields a crystalline endoperoxide which explodes at -10 °C upon attempted isolation.11

Hydroazulene Synthesis.

Fulvenes can react as a 2p-, 4p-, or 6p-electron system in cycloaddition reactions.1 6,6-Dimethylfulvene serves as a 6p-addend in a cycloaddition route to hydroazulene derivatives. Treatment of 1-diethylaminobutadiene (1) with 3 equiv of 6,6-dimethylfulvene at rt for 2 days yields a hydroazulene product (2) in 65% yield (eq 1). The isolated material is the product of a [6 + 4] cycloaddition followed by elimination of diethylamine.2,12

Alkene Protection.

The reaction of 2-hydroxymethyl-1,4-benzoquinone (3) with 6,6-dimethylfulvene results in the formation of a 1:1 Diels-Alder adduct. The [4 + 2] cycloaddition product (4) is isolated after subsequent alkene epoxidation. Following ketone reduction and hydroxy protection, a retro-Diels-Alder reaction is accomplished by heating in diglyme (eq 2). The conditions for this retro-cycloaddition are milder than those required for cyclopentadiene Diels-Alder adducts. Analogous reactions have been used in syntheses of DL-senepoxide and DL-crotepoxide.3,13,14

Substituted Fulvenes.

Reaction of the lithium anion of 6,6-dimethylfulvene with aldehydes at low temperature results in functionalization at the 7-position (eq 3).15 Regioselective allylation at the 7-position may be accomplished in the presence of a palladium(0) catalyst (eq 4).16

1. Neuenschwander, M. In The Chemistry of Double-Bonded Functional Groups; Patai, S., Ed.; Wiley: Chichester, 1989; Vol. 2, Part 2, pp 1131-1268.
2. Dunn, L. C.; Houk, K. N. TL 1978, 3411.
3. Ichihara, A.; Kobayashi, M.; Sakamura, S.; Sakai, R. T 1979, 35, 2861.
4. Smith, W. B.; Gonzales, C. JOC 1963, 28, 3541.
5. Thiele, J. CB 1900, 33, 666.
6. Thiele, J.; Balhorn, H. LA 1906, 348, 1.
7. Crane, G.; Boord, C. E.; Henne, A. L. JACS 1945, 67, 1237.
8. Stone, K. J.; Little, R. D. JOC 1984, 49, 1849.
9. Engler, C.; Frankenstein, W. CB 1901, 34, 2933.
10. Skorianetz, W.; Schulte-Elte, K. H.; Ohloff, G. HCA 1971, 54, 1913.
11. Harada, N.; Uda, H.; Ueno, H.; Utsumi, S. CL 1973, 1173.
12. Dunn, L. C.; Chang, Y.-M.; Houk, K. N. JACS 1976, 98, 7095.
13. Ichihara, A.; Oda, K.; Kobayashi, M.; Sakamura, S. TL 1974, 4235.
14. Oda, K.; Ichihara, A.; Sakamura, S. TL 1975, 3187.
15. Nyström, J.-E.; Byström, S. E.; Ristola, T.; Ekström, J. TL 1988, 29, 4997.
16. Nyström, J.-E.; Vågberg, J. O.; Söderberg, B. C. TL 1991, 32, 5247.

Charles G. Caldwell

Merck Research Laboratories, Rahway, NJ, USA

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