Synthesis of spirane-bridged rigidified oxalkyl cyclopentadienyl ligands

Methods for the preparation of constrained spirane-bridged oxalkyl indenyl ligands are described. The cis,cis-α,α′-spirane derivatives were synthesised in several steps from spiro[4.4]nonane-1,6-dione. Carbylation was achieved by Wittig methenylation. A subsequent stereoselective hydroboration by 9-BBN followed by peroxide treatment furnished the corresponding cis-methanol. Further manipulations provided the cis-carboxylic ester, which in a double Grignard reaction with α,α′-dichloro-o-xylene, furnished the corresponding indenyl derivative. The final products were cis,cis-α-(2-indenyl)-α′-(methoxy or methoxymethyl)spiro[4.4]nonanes.