Ylide, hydroxy oxido

The jS-oxido-ylides synthesis of trisubstituted olefins has also been applied to the synthesis of farnesol (127). The phosphonium salt (123) with the aldehyde (124) and formaldehyde gave the hydroxy farnesol derivative (125) which was transformed into farnesol (127) and into (126), a position isomer of Cj juvenile hormone. 

A stereospecific total synthesis of prostaglandins E3 and F3, containing an additional double bond in this side chain, starts from the optically active phosphonium salt 161. In this synthesis the ( )-13-double bond and the 15-hydroxy function are generated simultaneously by condensation of the chiral bicyclic aldehyde 163 with the P-oxido ylide 162 obtained by treatment of 161 with methyllithium. The corresponding phosphonium salt S) +)-161, already possessing the (Z)-configurated A17-double bond of prostaglandins, was prepared from (S)(—)-tartaric acid 1351 (Scheme 29). 

There are some additional potential complications with the control experiments. Loss of stereochemistry in method D can be due to product equilibration induced by the phosphine additive as already mentioned. Furthermore, equilibration in method A or E can occur because of competing (reversible) (x-deprotonation to give the oxido ylide 38 or the derived hydroxy ylide 39 (21c). The latter problem can usually 1% avoided by lowering the temperature or by using a weaker base for the deprotonation of the )5-hydroxyphosphonium salt 27 or 28 (21c). Nevertheless, positive equilibration results cannot be attributed to retro-Wittig reaction unless (1) crossover is also demonstrated or (2) labeling results can rule out the intervention of 38 or 39. 

Ylides of hydroxyquinones 416 were synthesized by treatment of 2-hydroxy-1,4-benzoquinones 415 with an equimolar amount of (diacetoxyiodo)benzene (Scheme 2.121) [560]. The most important member of this class, 2-oxido-3-(phenyliodonio)-l,4-naphthoquinone (417), was prepared similarly by treatment of 2-hydroxy-1,4-naphthoquinone (lawsone) with an equimolar amount of (diacetoxyiodo)benzene [561]. 

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