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■ The Isomerization of Hydrogenated Adducts Obtained from 1,4-Phthalazinedione

Manuel Lora-Tamayo,* Pilar Navarro, Dolores Romero, and José Luis Soto

*President of the Centro Nacional de Química Orgánica, C. S. I. C., Juan de la Cierva 3 , E-28006 Madrid, Spain

Abstract

The hydrogenated adducts obtained from 1,4-phthalazinedione with 1-vinylcyclohexene I and 1-vinylcyclopentene III, are isomerized with concentrated sulfuric acid to give the spiro-compounds II and IV respectively by contraction of ring C.
This ring contraction also takes place in the hydrogenated adducts X, XII, XIV and XVI corresponding to 1,3-pentadiene, 2-methyl-1,3-pentadiene and 2,4-hexadiene derivatives and it does not occur in the hydrogenated adducts of isoprene and 2,3-dimethylbutadiene derivatives XVIII and XIX.
In all the cases we have studied, the isomerization takes place when of the two carbon atoms involved in the ring contraction, the adjacent to the nitrogen atom is substituted, being not necessary any substitution on the other carbon atom.
The mechanism of the reaction is discussed.