Complex reducing agents unsaturated carbonyl compounds

Triethylammonium formate is another reducing agent for q, /3-unsaturated carbonyl compounds. Pd on carbon is better catalyst than Pd-phosphine complex, and citral (49) is reduced to citronellal (50) smoothly[55]. However, the trisubstituted butenolide 60 is reduced to the saturated lactone with potassium formate using Pd(OAc)2. Triethylammonium formate is not effective. Enones are also reduced with potassium formate[56]. Sodium hypophosphite (61) is used for the reduction of double bonds catalyzed by Pd on charcoal[57]. 

Asymmetric reduction of a,/ -unsaturated carbonyl compounds using chiral complexes (Section 5.4.1, p. 521) could feasibly lead to optically active allylic alcohols. Other reducing agents which have some merit of regioselectivity, but not stereoselectivity, are sodium cyanoborohydride,244 and sodium boro-hydride in the presence of lanthanide salts.245... 

Other cobalt catalysts that have been used for enantioselective C—C double bond reduction of a,/ -unsaturated carbonyl compounds are vitamin B12 in combination with zinc/acetic acid (up to 33% ee)S7 and bis(dimcthylglyoximato)cobalt(II) (12) with chiral amines as cocatalysts88 and molecular hydrogen as reducing agent. The best results have been obtained with complex 12 and quinine or (2.S )-A -[(/ )-1 -phenethyl]-2-quinuclidinecarboxaniide (hydrogenation of 1,2-diphenyl-2-propen-l-one 49% ee A, /V -dimethyl-5-benzylidenehydantoin 79% ee). 

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