Synthese und Abfangen eines hochgespannten Cyclopropens

Two synthetic sequences towards tricyclo[3.2.1.0]octa-2(4),6-diene (12) have been investigated starting with 1,1,2-tribromo-2-(trimethylsilyl)cyclopropane (13)(Schemes 1 and 2).F--induced elimination 13→14a and reaction with cyclopentadiene gives tricyclic dibromo precursor 15a in a 87% yield. Subsequent reaction of 15a with t-BuLi produces the highly strained cyclopropene 12 which has been trapped by [4+2] cycloaddition with diphenylisobenzofuran (40% yield). NMR-spectroscopic evidence of 2,4-disubstituted tricyclo[3.2.1.0]oct-6-enes 15a, 15b, and 16 (Table) is briefly discussed.