Triphenylphosphite, hydrogenation

The Osmium cluster Os3(CO)12 and clusters in the presence of various phosphines and triphenylphosphite have been utilized for the hydrogenation of cinnamaldehyde and crotonaldehyde (Table 15.7) [36]. The results show that good yields of unsaturated alcohols can be obtained by using a large excess of phosphine at elevated hydrogenation temperatures. 

According to earlier reports, palladium-catalyzed conversion of e <7o-5-vinylnorborncnc with hydrogen cyanide in the presence of tetrakis(triphenylphosphite)palladium(0) led to a tricyclic adduct with tram addition of cyanide and the vinyl group32,33. 

In the presence of deuterium, the 24 ortho hydrogens of 27 are exchanged for D at room temperature (48). It is pertinent to note that 27 undergoes a reductive elimination of H2 rather than HCl. When phenol was added to solutions of 27, the phenol was also ortho deuterated indicating that phenol was exchanging with the phenoxy groups of the triphenylphosphite. 

The synthesis of 3 may be simplified further by linking the C20- units 59 or 60 oxidatively or reductively, respectively. Thus reduction of 60 with low-valency titanium compounds [64] or oxidation of 59 with triphenylphosphite-ozone adduct [65] afford 3 in yields of 85% and 75%, respectively. In a process developed at BASF the phosphonium salt 59 is reacted with hydrogen peroxide in aqueous alkaline solution [62]. After separation of triphenylphosphine oxide and thermal isomerization, (all- )-3 conforming to type specifications is obtained in yields of approximately 70% based on vitamin A acetate (26) (Scheme 17). 

If triphenylphosphite [149] or some other phosphorus compounds [928, 1037] with a more complicated structure [928] are used as catalyst modifiers, no such hydrogenation is observed but high yields of aldehydes are obtained. 

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