Reactivities of Stable Rotamers. XXXII. Chlorodecarboxylation of 3-(1,4-Dimethyl-9-triptycyl)-3-methylbutanoic Acid Rotamers

Rotational isomers of the title carboxylic acid were treated with lead(IV) acetate in the presence of lithium chloride or benzyltriethylammonium chloride in benzene. The ap-isomer afforded a chloride, which was expected from normal chlorodecarboxylation, in addition to a cyclized compound, which was produced by radical addition to a near-by benzene ring. By contrast, the sc-isomer afforded no normal chloride, but a benzylic chloride, which was formed by hydrogen transfer to the radical site in the 9-substituent from the benzylic position, was the main product. In addition, an acetonyl ester of the original sc-carboxylic acid and a small amount each of 1-acetoxymethyl compound and an olefin were obtained. Possible mechanisms of formation of these compounds are discussed on the ground of the stability of the benzylic radical and participation of a methyl group.