Reactivities of Stable Rotamers. VIII. Difference in Reactivities of 1,2,3,4-Tetrachloro-9-(2-halo-1,1-dimethylethyl)triptycene Rotamers in Lewis Acid-catalyzed Reactions

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Abstract
±sc-1,2,3,4-Tetrachloro-9-(2-chloro-1,1-dimethylethyl)triptycene was found to react in the presence of titanium(IV) chloride at room temperature to give an isomeric mixture of 1,2-dimethyl-7,8,9,10-tetrachloro-1,2,6,10b-tetrahydro-6,10b-o-benzenoaceanthrylenes. The structure of the latter was confirmed by independent syntheses. In contrast, the ap conformer of the former did not give any sign of the reaction under the same conditions but reacted when antimony(V) chloride was added to give the same mixture. Careful examination of the reaction mixture suggests that the starting material was rapidly converted to (E)-1,2,3,4-tetrachloro-9-(1-methyl-1-propenyl)triptycene and cyclization followed. Action of silver nitrate on ±sc-9-(2-bromo-1,1-dimethylethyl)-1,2,3,4-tetrachlorotriptycene afforded a mixture of the stereoisomers of the olefin while the ap form remained intact.

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