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-cydopentadienyl 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 XXX. 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.

Using a simple apparatus addition of 2-alkenyl halides to precondensed active Mg in THF gave clean solutions of 2-alkenylmagnesium halides which on carbonation furnished β,γ-unsaturated carboxylic acids in high yields.

AbstractCyclopropylmethyl bromide reacts readily at −75° with a Mg/THF slurry formed by evaporation of Mg in a rotating‐solution reactor to yield after carbonation cyclopropyl acetic acid and 4‐pentenoic acid in a ratio of 11:1. Addition of benzaldehyde to the Grignard solution again predominantly yields the addition product containing the cyclopropylmethyl unit. Using the same low temperature Grignard method, benzocyclobutenyl acetic acid is isolated upon carbonation of the Grignard reagent derived from the corresponding bromide, whereas under normal conditions o‐vinylphenylacetic acid, the product corresponding to ring cleaved Grignard is obtained.