Reaction with phosphorous ylids

WITTIG, GEORGE (1897-1987). A University of Heidelberg professor who won the Nobel prize for chemistry in 1979 along with Herbert C. Brown of Purdue. Wittig s research showed that phosphorous ylids react with ketones and aldehydes to form alkenes. This reaction is used a great deal in the synthesis of pharmaceuticals and other complex organic substances. 

A related triazole synthesis utilizes phosphorous ylids, such as 264. The initially formed triazenes cyclize with elimination of triphenylphosphine oxide. The reaction proceeded sluggishly with phenyl azide, but good results have been obtained with acyl or sulphonyl azides. Tosyl azide and 264 yielded 98% of the 1-tosyl-triazole 265. The tosyl group could be removed by solvolysis in boiling ethanol... 

Wittig reaction The reaction of an aldehyde or ketone with a phosphorous ylid (also called a phosphorane), Ph3P+CR2, to give an unsaturated adduct. 

In terms of its chemical reactivity, an ylid such as 126 may be viewed as a phosphorus-stabilized carbanion that will undergo acyl addition with an aldehyde or a ketone. When this ylid is mixed with cyclohexanone (80), there are two isolated products. The one that is more interesting to an organic chemist is methylenecyclohexane (129), formed in 52% yield the other is tri-phenylphosphine oxide, 130. It is obvious that 129 is not the expected acyl addition product. Formation of 130 indicates that the carbon atom of the ylid has been transferred to the ketone, but the oxygen atom of the ketone has been transferred to the phosphorous atom. Analysis of the reaction shows that the oxygen atom is lost from the ketone, and the CH2 unit of ylid 126 is transferred to form a new C=C bond (in green in the illustration). What is the mechanism ... 

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