Cycloaddition of isopropylcyclopentadienes and dichloroketene, and the solvolysis of the adducts

Dichloroketene was allowed to react with a mixture of 1- and 2-isopropylcyclopentadienes (1 and 2) to afford a mixture of the cycloadducts 5, 7 and 8. The adducts 5 and 8 were isolated, and an adduct 7 was obtained as a mixture with 5. The structures of these adducts were assigned. Some derivatives of the adducts were prepared and their structures discussed. A mixture of β- and γ-thujaplicins (19 and 20) were produced after a mixture of the adducts was heated in acetic acid containing potassium acetate, 2-Isopropylcyclopentadiene (2) was prepared from cyclopentadienylmagnesium bromide and isopropyl tosylate, and the adduct obtained gave only β-thujaplicin under the same solvolytic reaction conditions.