Regiospecific Reagents for Allyl Anions

The allyl phosphine oxide approach to diene and polyene synthesis has been used by Lythgoe28- in his vitamin D3 synthesis, and by Pattenden29-1 in syntheses of compounds such as 31. 

The main classes of allyl phosphine oxide which cannot be used in diene syntheses, as they react in the 7-position30, are those with an aryl group in the a-posi-tion 32, or with a four 33 or five 34 membered ring. Those with just one a-sub-stituent and no 0- or 7-substituents 35 also give some 7-adduct31.  

Synthesis of Allyl Alcohols from a Vinyl Anion Equivalent 

The carbonyl adducts of allyl phosphine oxides, e. g., 24 and 29 can also be used to make allyl alcohols32 by the reductive removal of the Ph2PO group with lithium aluminium hydride a reaction involving transposition of the double bond, e. g., 24 36. In this approach, the allyl anion of 23 is a reagent for the vinyl anion synthon 37. 

In open chain compounds, the E isomer of the allyl alcohol is formed stereo-selectively, e. g., 38 in 80% yield32). 

---