Beschreibung:
<jats:p><jats:bold>New Pathways to Precursors of Pentalene</jats:bold></jats:p><jats:p>Pentalene dimers <jats:bold>2</jats:bold> and <jats:bold>3</jats:bold> are easily available in moderate yields by CuCl<jats:sub>2</jats:sub>‐induced oxidative coupling of dilithium‐pentalenediide (<jats:bold>5</jats:bold>) (<jats:italic>Scheme 1</jats:italic>). On the other hand, NBS bromination of 1,5‐dihydropentalene (<jats:bold>4</jats:bold>) or of 1,2‐dihydropentalene (<jats:bold>8</jats:bold>) gives unstable 1‐bromo‐1,2‐dihydropentalene (<jats:bold>9</jats:bold>), while subsequent <jats:italic>in</jats:italic>‐<jats:italic>situ</jats:italic> elimination with Et<jats:sub>3</jats:sub>N exclusively gives <jats:italic>syn</jats:italic>‐<jats:italic>cis</jats:italic>‐pentalene dimer <jats:bold>2</jats:bold> in moderate yields (<jats:italic>Scheme 3</jats:italic>). NMR‐Spectroscopic evidence for compounds <jats:bold>2</jats:bold>, <jats:bold>3</jats:bold>, and <jats:bold>9</jats:bold> is presented, and mechanistic alternatives for the formation of pentalene dimers <jats:bold>2</jats:bold> and <jats:bold>3</jats:bold> are discussed.</jats:p>