Phosphorane methylenetriphenyl

The teal value of the Wittig reaction is that it yields a pure alkene of defined structure. The C=C bond in the product is always exactly where the OO group was in the reactant, and no alkene isomers (except E,Z isomers) are formed. For example, Wittig reaction of cyclohexanone with methylenetriphenyl-phosphorane yields only the single alkene product methylenecyclohexane. By contrast, addition of methylmagnesium bromide to cyclohexanone, followed by dehydration with POCI3, yields a roughly 9 1 mixture of two alkenes. 

The second synthesis of 654 and 655 makes use350,351 of the Wittig reaction. The (methylthio)methyl ether 656 is converted into the chloromethyl ether 657, which reacts with triphenylphosphine to yield a crystalline phosphonium salt (658). Reaction of 658 with phenyllithium gives a phosphorane, treatment of which with acryl-aldehyde leads to ethers 654 and 655 in —50% yield. Pure trtms-diene 654 was obtained352 in a reversed way consisting in preparation of a sugar ether acrylaldehyde (660) by replacement of the p-tolylsulfonyl group in 659, followed by reaction of 660 with methylenetriphenyl-phosphorane. 

Methylenetriphenyl phosphorane has been used for the synthesis of a variety of cyclic compounds by a combination of ring closure and nucleophilic ylid reaction A new simple synthesis of isoflavones via a thallium(III) acetate-promoted rearrangement of chalcones has been published ... 

Studies of the chemical behavior of jS-ketometalloid compounds have not been extensive to date. The compounds are relatively unstable to both acid and base, the acyl group being cleaved from the metalloid (97, 99,100). Similar behavior was reported for the reaction of the ketones phenacyltri-phenylsilane and phenacyltriphenylgermane with methylenetriphenyl-phosphorane, since the major product of the reactions was the ketone... 

The ylide (35), prepared from base treatment of the methylenetriphenyl-phosphorane-isobutene oxide adduct, has been shown to react with steroidal aldehydes to give the (E)-homoallylic alcohol stereoselectively [equation (6)], especially at low temperatures. 

In 1953 Wittig and Geissler discovered that methylenetriphenyl-phosphorane reacted with benzophenone to give 1,1-diphenylethyl-ene and triphenylphosphine oxide in almost quantitative yield. The phosphorane was prepared from triphenylmethylphosphonium bromide and phenyllithium. 

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