Stereoselective Syntheses of Spirane Bridged Semi-titanocenes

Abstract

The synthesis of bidentate cyclopentadienyl-alkoxide ligands and their complexation to titanium are described. The focus has been on methodology for stereoselective synthesis of ansa half-sandwich titanocenes with rigid C₂- and C₃-bridges which are embedded in a spirane scaffold. Intermediate reactions involve tandem acylation-alkylation in the conversion of a carbonyl carbon into a quaternary carbon and rhodium(I)-effected spiroannulations. Titanocene formation involved reaction between the dilithiated ligand and titanium(III) chloride, and subsequent oxidation of the trivalent titanium with lead(II) chloride whereby the semi-metallocene was formed.

Key words

spirane scaffold - ansa semi-titanocenes - C₂- and C₃-spirane bridges - geminal acylation-allylation - rhodium(I)-catalyzed spiroannulation

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