New Pathways to Precursors of Pentalene

Article abstract of DOI:10.1002/hlca.19970800520

Pentalene dimers 2 and 3 are easily available in moderate yields by CuCl2-induced oxidative coupling of dilithium-pentalenediide (5) (Scheme 1).On the other hand, NBS bromination of 1,5-dihydropentalene (4) or of 1,2-dihydropentalene (8) gives unstable 1-bromo-1,2-dihydropentalene (9), while subsequent in-situ elimination with Et3N exclusively gives syn-cis-pentalene dimer 2 in moderale yields (Scheme3).NMR-Spectroscopic evidence for compounds 2. 3. and 9 is presented, and mechanistic alternatives for the formation of pentalene dimers 2 and 3 are discussed.