Titanium-Catalyzed Hydroalumination of Conjugated Dienes: Access to Fulvene-Derived Allylaluminium Reagents and Their Diastereoselective Reactions with Carbonyl Compounds

摘要

The described titanium-catalyzed hydroalumination of conjugated dienes opens up a new way to allylaluminium reagents. The reaction is carried out by using diisobu-tylaluminium hydride (DIBAL-H) and a catalytic amount of [Cp_2TiCI_2] (Cp = cyclopentadienyl). When applied to monoand disubstitued pentafulvenes, this reaction proceeds in a highly endocyclic manner. The formed allylaluminium compounds react regio- and stereoselectively with both alde hydes and ketones to afford homoallylic alcohols that are suitable synthons for functionalized cyclopenta nones. An extension of this methodology to simple dienes was also investigated. In the proposed mechanism, the initially formed bimetallic species (Ti/AI) are involved in the two possible catalytic cycles with a direct hydroalumination or/and a hydroti-tanation followed by a titanium to aluminium trans metallation.