9-[l-(Methylthio)ethylidene]bicyclo[4.2.1]nonane (41).This compound is prepared and isolated as described for 15; yield 68%. Extremely pure product was obtained with the aid of high-performance LC (hexane): MS, m/e 196; 1H NMR (CDC13) 3.30 (m, 1), 3.03 (m, 1), 2.20 (s, 3), 1.97 (s, 3), 2.0-1.2 (m, 12). syn -9-Acetyl-9-chlorobicyclo[4.2.1]nona-2,4,7-triene (44). To a solution of vinyl ether 13 in S02 at -78 °C was added an excess (3 equiv) of S02C1F. The reaction was instantaneous. The reaction mixture was poured onto saturated aqueous NaHC03 and extracted into Et20. After the extract was dried (MgS04) and concentrated, hydrolysis of the intermediate ester was effected by passing the reaction mixture through a column of Si02 (CHC13 as eluent): NMR (CDC13) 6.0-5.7 (m, 4), 5.30 (d, 2), 3.53 (d, 2), 2.27 (s, 3); MS, m/e 194, 196. Carbocation Generation. NMR samples were prepared by condensing S02 from a gas cylinder into an NMR tube containing the substrate and cooled in a dry ice/acetone bath. The concentration of the samples was about 100-200 mg/0.3 mL of solvent. To the cooled solution, was carefully added freshly prepared HFS03/SbF5 (5:1) via the wall of the tube. In the case of the unsaturated substrates 13, 15, and 19,1 equiv of acid was used; the cations 47a-c were generated with a twofold excess of acid. Mixing was effected by shaking the samples vigorously with the aid of a vibromixer. Samples were checked with 60-MHz NMR spectroscopy. Spectroscopic investigations were performed in the temperature range of -100 to -30 °C. Quenching was effected by pouring the samples onto saturated aqueous NaHC03.
AppendixTables IV and V contain collections of various and 13C NMR spectral data, respectively.
