4-(1-HYDROPEROXY-1-METHYLETHYL)-1,3-CYCLOPENTADIENYL METHYL KETONE: ITS FORMATION FROM α-TERPINEOL AND BEHAVIOR AS A DIMETHYLFULVENE EPOXIDE.

Article abstract of DOI:10.1016/S0040-4020(01)87395-6

Ozonolysis of α-terpineol (1) then steam distillation in presence of acid gives the known 4-isopropylidenecyclopentenyl methyl ketone (4).This is oxidized in air to 4-(1-hydroperoxy-1-methylethyl)-1,3-cyclopentadienyl methyl ketone (10), a compound frequently reacting as if it were one of the elusive dimethylfulvene epoxides.It is converted by silica gel to two dimers (12, 13) of 2-acetyl-6,6-dimethylfulvene epoxide (19).Catalytic reduction of the dimers occurs mostly by exo addition of hydrogen to the conjugated double bond, and thermolysis of the dimers yields 4-acetyl-6,6-dimethylcyclohexa-2,4-dienone (20).With triphenylphosphine the hydroperoxide (10) yields two <6+4> dimers of 2-acetyl-6,6-dimethylfulvene (26).This is the first reported isolation of <6+4> dimers of a fulvene.The hydroperoxide (10) adds diazomethane to give an unstable pyrazoline (28); this pyrazoline loses nitrogen to yield a single isomer o' 5-acetyl-3',3'-dimethylbicyclo<3.1.0>hex-3-ene-2-spiro-2'-oxirane (29).Catalytic hydrogenation of the latter involves ring opening of the epoxide.