Sodium hydride phosphonium ylide synthesis

Intermediates 18 and 19 are comparable in complexity and complementary in reactivity. Treatment of a solution of phosphonium iodide 19 in DMSO at 25 °C with several equivalents of sodium hydride produces a deep red phosphorous ylide which couples smoothly with aldehyde 18 to give cis alkene 17 accompanied by 20 % of the undesired trans olefin (see Scheme 6a). This reaction is an example of the familiar Wittig reaction,17 a most powerful carbon-carbon bond forming process in organic synthesis. 

The cyclohexanone (S3), an intermediate for the synthesis of thromboxane antagonists, has been prepared by a combination of phosphine oxide- and phosphonium ylide-based olefinations.30 Reaction of the lactone (50) with methoxymethyldiphenylphosphine oxide anion gave a poorly characterized adduct (presumably (51)) which on reduction with sodium borohydride, followed by treatment with sodium hydride gave the vinyl ether (52) in 80% overall yield from (SO) (Scheme 8). Further modification gave the required cyclohexanone (53). 

Stepwise deprotonation of methylenebis(triorgano)phosphonium salts with bases yields carbodiphosphoranes via intermediate semi-ylide salts, which may also be accessible by alkylation or phosphinol-ation of corresponding alkylidenephosphoranes (equation 118). " It depends on the starting phosphonium salt and the base whether the intermediate ylide salts can be isolated or not. Suitable bases are sodium amide, alkali metal hydrides, alkylidenetrialkylphosphoranes, potassium and lithium orga-nyls. For the synthesis of hexaphenylcarbodiphosphorane improved methods have been reported by which this compound may be generate without isolation of the ylide salt and on a large scale. 

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