Lithium diphenylphosphide epoxides

In 1955 Wittig et al. found that triphenylphosphine could induce the deoxygenation of epoxides at 200 Mechanistically, this process probably involves anti opening of the epoxide followed by syn elimination of triphenylphosphine oxide from a betaine intermediate. Accordingly, the reaction proceeds with inversion of stereochemistry, which means that franj-ejjoxides give ci5-alkenes. The systems of bis(di-methylamino)phosphorous acid/butyllithium, o and lithium diphenylphosphide have been examined... 

Olefin inversion.2 Lithium diphenylphosphide in THF opens epoxides stereo-specifically quatemization of the crude product with methyl iodide leads to betaines, which fragment under mild conditions (25°) to give an olefin and methyldiphenyl-phosphine oxide. The product olefins are formed with inversion of stereochemistry relative to the starting epoxide owing to SN2 epoxide opening followed by cis elimination of the phosphine oxide. Thus the oxide of fraus-stilbene (1) is converted into the betaine (2), which at 25° gives cis-stilbene (3) in 95% yield overall. The conversion is stereospecific (> 98%). Similarly cis-stilbene can be converted into franx-stilbene. 

Treatment of epoxides with lithium diphenylphosphide followed by oxidation gives i3-hydroxydiphenylphosphine oxides which can be fragmented to olefins stereospecifically, thus constituting an olefin inversion (Scheme 2). 

Lithium diphenylphosphide in THF reacts with epoxides stereo-specifically. Quaternization of the phosphorus of the product generally led directly to the alkene with inversion of stereochemistry relative to the starting epoxide ... 

Treatment of the epoxides (257) with lithium diphenylphosphide gives stereospecific ring-opening and quaternization of the crude product yields the betaines (258). The latter generally fragment under the conditions of... 

The methods employed in the synthesis of the individual components have tended to follow those for monoenes, namely via acetylenic intermediates (232—236), by allylic Grignard coupling 232, 237), and by Wittig reaction 234, 238). Sonnet (259) isomerized the 7Z,11Z- and 7Z,ll -isomers (as their tetrahydropyranyl ethers) to the 1E,UE- and 7 , llZ-isomers, respectively, by treatment of the corresponding bis-epoxides with lithium diphenylphosphide and then methyl iodide. 

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