[2175-91-9] · C8H10 · 6,6-Dimethylfulvene · (MW 106.18)
Physical Data: bp 40-43 °C/8 mmHg.4
Form Supplied in: liquid; commercially available.
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
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
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
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
Charles G. Caldwell
Merck Research Laboratories, Rahway, NJ, USA