Ozone-triphenylphosphine adduct

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). 

Phosphines and phosphites are readily oxidized by ozone (81). The 1 1 adducts have pentacovalent phosphorus structures (82). Ozonides are reductively cleaved by triphenylphosphine (83). 

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