Thermal Isomerization of Cyclopropylidenespiropentane—An Unusual Route to Tricyclopropylidene ([3]-Rotane)

✍ Scribed by Dr. Lutz Fitjer; Prof. Dr. Jean-Marie Conia

• Book ID: 101547983
• Publisher: John Wiley and Sons
• Year: 1973
• Tongue: English
• Weight: 205 KB
• Volume: 12
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.197307611

✦ Synopsis

Only after the steric contribution to the I3C-NMR shift has been largely eliminated by the comparisons ( 1 ) / ( 2 ) and ( 3 ) / ( 4 ) is it possible to recognize the high field shift for the bridging C atoms C , and CB of the annulenes which is partially due to the ring current effect. From this it is clear that no ring current is induced in (31, and the compound is not to be regarded as homoaromatic. This finding contradicts the interpretation of the I3C-NMR spectrum of ( 3 ) by Wenkert et who considered ( 3 ) to be the first neutral homoaromatic compound. Further, these authors assigned the resonance of C, incorrectly and thus fortuitously established agreement with the resonance frequency of C-1,6 i n 1,6-methano[IO]annulene (1 14.6 ppmCz1). Figure 1 shows the relevant off-resonance experiment['], whereby the signal at 136.4ppm can be unambiguously recognized as the C, resonance['O].