Conformations of Internal Cyclopropylcarbinyl Cations (Benzobicyclo[ 4.1 .O]heptyl Cations) and Their Rearrangements to Naphthalenium Cations

Ionizations of 2-substituted l,l-dimethyl-3,4-methano-1,2,3,4-tetrahydronaphthalen-2-ols (8) (3,3-dimethylbenzobicyclo[4.1 .O]heptan-2-ols) in FS03H/S02CIF at -1 30 O C do not yield the corresponding 2-cations but benzylic (4-) cations 10 as a result of cyclopropylcarbinyl~yclopropylcarbinyl rearrangements. At higher temperatures, 10a and 10b undergo a further series of rearrangements to yield ultimately dialkylnaphthalenium cations. Comparison of the JCmH values of the internal cyclopropylcarbinyl cations with those of model bicyclic ketones give AJ values of approximately 20 Hz, indicating that in all cases bisected cyclopropylcarbinyl geometries prevail. Conformations of these and related cations and of the bicyclic ketones are discussed. Recently it has been reported that when 1,6methano[lO]annulene is treated with FS03H/S02CIF a t -100 OC, a monoprotonated cation is formed, which rearranges a t -60 O C to a cyclopropylcarbinyl cation ( 1).2 Observation of vicinal coupling