1972 Volume 45 Issue 7 Pages 1999-2003
Transient 8,8-dimethylisobenzofulvene (5) was generated by thermal decomposition of two materials; one is formally an adduct of cyclopentadienone with 9-isopropylidenebenzonorbornadiene (6), and the other an adduct of 3,6-di(2′-pyridyl)-S-tetrazine with 6. The former was prepared by cycloaddition of 6 to tetrachlorodimethoxycyclopentadiene followed by dechlorination giving a ketal, then hydrolysis of the ketal function. Generation without any trapping reagent instantaneously yielded one kind of dimer of a stereospecific structure. In the presence of dimethyl maleate, dimethyl 9-isopropylidenebenzonorbornene-exo,cis-2,3-dicarboxylate and its endo-cis isomer were formed. In the presence of dimethyl fumarate, the trans isomer was obtained. Trapping with tropone led to a 1 : 1 adduct resulting from participation of the exocyclic C2–C8 double bond in 5. All attempts to isolate 5 or prepare a stable metal complex of 5 by conventional means were unsuccessful.
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