Titanium and Zirconium Hydride-Catalyzed Regioselective Isomerization of 1,4-Dihydrofulvenes: Access to 1-Substituted 1,2-Dihydrofulvenes.

Zirconium hydride-catalyzed C═C double bond migration from nonconjugated to conjugated dienes is described. Applied to 1-substituted 1,4-dihydrofulvenes, the migration leads selectively to 1-substituted 1,2-dihydrofulvenes. The C═C double bond migration can also be catalyzed by titanium hydride, allowing a one-pot procedure to provide 1-substituted 1,2-dihydrofulvenes from pentafulvenes via two titanium-catalyzed steps. This sequence was proven to be temperature-dependent, allowing the selective access to a conjugated or nonconjugated adduct by a simple temperature tuning. The synthetic potential of the methodology was illustrated by the diastereoselective synthesis of a polyhydroxycyclopentane.