Hydrocyanation of Other Dienes

A number of dienes are hydrocyanated in the presence of Ni[P(0-o-tolyl)3]4 as the catalyst. Studies are dealing with cumulated, conjugated, and non-conjugated systems. Table 4 summarizes the results of diene hydrocyanation. 

The hydrocyanation of 1,3-cyclohexadiene does not require the presence of Lewis acids, in contrast to the results found in the case of HCN addition to mono-olefins [11, 74, 75]. 

Hydrocyanation of aldehydes opens access to the synthetically valuable cyanohydrins, precursors for hydroxycarboxylic acids, a-hydroxyketones and /S-ami-noalcohols. Applying the principles of homogeneous catalysis to this reaction it is possible to obtain cyanohydrins in the optically active form, depending on how well the catalyst-ligand system is adapted to the substrate. 

When certain cyclodipeptides are used as catalysts for the enantioselective formation of cyanohydrins, an autocatalytic improvement of selectivity is observed in the presence of chiral hydrocyanation products [80]. A commercial process for the manufacture of a pyrethroid insecticide involving asymmetric addition of HCN to an aromatic aldehyde in the presence of a cyclic dipeptide has been described [80]. Besides HCN itself, acetone cyanohydrin is also used (usually in the literature referred to as the Nazarov method), which can be activated cata-lytically by certain lanthanide complexes [81]. Acetylcyanation of aldehydes is described with samarium-based catalysts in the presence of isopropenyl acetate cyclohexanone oxime acetate is hydrocyanated with acetone cyanohydrin as the HCN source in the presence of these catalytic systems [82]. 

A high asymmetric induction was found for the silylcyanation of benzaldehyde in the presence of a slightly altered Sharpless reagent [83]. The classical Sharpless reagent in the presence of two equivalents of 2-propanol [(L-Dipt(Ti)OPr )2] pro- 

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