Reaction of ArSCl (Ar = phenyl or ortho-nitrophenyl) withendo-tricyclo[6.2.1.@~7]undeca-4,9diene-3,6dione
(1) results in arm' addition across the norbcnnene carbon-carbon double bond with concomitant aromatization of the cyclohexenedione ring, thereby affording 4 (87%) and 5 (63%), respectively. The corresponding reaction of PhSCl with 1 in the presence of added Ag(l) proceeds via polar addition across the norbomene carbon-carbon double bond with concomitant intramolecular nucleophilic trapping of au intermediate episulfonium ion by a distant C=O group, thereby affording 6 (57% yield). The xeaction of PhICl2 with 1, when carried out in the presence of SbCls or AgBF4, pmcceds with concomitant Wagner-Meerwein rearraugement and aromatization to afford adducts 7a and t& respectively. Introduction. endo-Tricyclo[6.2.1.@~$mdeca-4,9-diene-3~6dione (l), the exclusive product that results via Diels-Alder [4 + 21 cycloaddition of cyclopentadiene to p-benzoquinone.1 has been employed frequently as an intermediate in the synthesis of substituted pentacyclo[5.4.0.02fi.@~t~.ti~9]undecanes.~ In addition, the mode of addition of electrophiles to the isolated [norbomene C(2)-C(3)] carbon-carbon double bond in 1 has been studied. Interestingly, the addition of BQ (1 equivalent) to 1 has been reported by Singh and Verma3 to affd exclusively the conesponding dibromide. 2, which results via stereoselective exo,cis addition (Scheme 1). Scheme 1 This mode of addition is unusual, since electrophilic addition of bromine to nonconjugated alkenes generpllyprooeeds s&reoselectively anti (via the cmsponding bromonium ion intermediate)4 and only 9933