Asymmetric trimethylsilylcyanation of benzaldehyde catalyzed by (salen)Ti(IV) complexes derived from (R)- and/or (S)-4-hydroxy-5-formyl[2.2]paracyclophane and diamines

Benzaldehyde has been asymmetrically trimethylsilylcyanated, using chiral (salen)Ti(IV) catalysts 1a and 1b, 20 and 2b, 3a and 3b prepared in situ from titanium tetraisopropoxide and the Schiff's bases derived from (R)- or (S)-4-hydroxy-5-formyl[2.2]paracyclophane [(R)- and (S)-FHPC] and diaminoethane (EDA) (catalysts 1a or 1b); (R)- or (S)-FHPC and 1,3-diaminopropane (PDA) (catalysts 20 or 2b); (R)- or (S)-FHPC and (1R,2R)-1,2-diaminocyclohexane [(1R,2R) CHDA] (catalysts 3a and 3b). Surprisingly, la and Ib were found to be the most efficient catalysts whereas both enantiomers of 2 were completely inactive. The maximum e.e. of 84% (S) at -78 degrees C was obtained in the reaction catalysed by Ib at 5-10 mol%. The catalyst could be precipitated with hexane from the reaction mixture and reused. (C) 1997 Published by Elsevier Science Ltd.