Asymmetric cyanohydrin synthesis using an aluminium(salan) complex

作者：North Michael^*; Stewart Emma L; Young Carl

来源：Tetrahedron: Asymmetry , 2012, 23(15-16): 1218-1225.

DOI：10.1016/j.tetasy.2012.07.011

The asymmetric addition of trimethylsilyl cyanide to aldehydes catalysed by chiral metal(salan) complexes has been investigated. Salan complexes of titanium and vanadium displayed only low catalytic activity, but a bimetallic aluminium(salan) complex gave high levels of catalytic activity and reasonable asymmetric induction when used with triphenylphosphine oxide as a cocatalyst. Mechanistic studies showed that the reactions were first order in catalyst and aldehyde concentrations, but zero order in trimethylsilyl cyanide and triphenylphosphine oxide concentrations. A Hammett analysis indicated that there was no significant change in the electron density at the aldehyde benzylic position during the rate determining step of the catalytic cycle. On the basis of the kinetic data, a catalytic cycle is proposed which accounts for the differences observed between [Al(salen)](2)O and [Al(salan)](2)O based catalysts.

• 出版日期2012-8-31