Aldehydes, catalytic chemoselective reducing

The highly efficient catalytic system for the chemoselective transfer hydrogenation of aldehydes was reported by Xiao et al. [52]. This system consisted of [Cp IrCl2]2 (1), a diamine and HCOONa, and worked on water and in air. A wide range of aromatic aldehydes were reduced to the corresponding primary alcohols in a highly chemoselective manner some representative examples are summarized in Table 5.9. 

Aluminum tris(2,6-diplienylphenoxide) (ATPH), an aluminum-based Lewis acid with bulky substituents, is valuable as an extremely selective activator of less hindered aldehyde carbonyls (Scheme 10.8) [36]. In competitive aldol reactions of two different aldehydes, more fhan one equivalent of ATPH achieves highly chemoselective functionalization of less hindered aldehydes. Unfortunately, catalytic use of ATPH reduces the chemical yield and chemoselectivity. In contrast, a catalytic quantity of aluminum bis(trifluoromethanesulfonyl)amide 13 can promote the chemoselective aldol reaction. 

The hydrogenation of a,j0-unsaturated aldehydes to allylic alcohols in quantitative yields in j -PrOH is catalysed by [FeF(P(PhPPh2)3)][BF4] in the presence of trifluo-roacetic acid. The catalyst could reduce a broad range of aromatic and aliphatic aldehydes in the presence of other reducible moieties (ketones, olefins, esters, etc.) with high chemoselectivity. Computational calculations and detection of the hydride species [FeH(H2)(P(PhPPh2)3)]", in situ, suggest a catalytic cycle. ... 

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