Pentalene dimers 2 and 3 are easily available in moderate yields by CuCI,-induced oxidative coupling of dilithium-pentalenediide (5)(Scheme f). On the other hand, NBS bromination of 1, 5-dihydropentaIene (4) or of 1.2-dihydropentalene (8) gives unstable 1 homo-I, 2-dihydropentalene (9), while subsequent in-siru elimination with Et, N exclusively gives syn-cis-pentalene dimer 2 in moderdle yields (Scheme 3). NMR-Spectroscopic ...
