Alkenes from alkenyl phosphates

The cleavage of carbon-oxygen bonds from alkenyl or aryl phosphates can be accomplished under reductive conditions with a low valent metal. As vinyl phosphates can be formed readily from ketones, this procedure provides a method to convert a ketone to an alkene. For example, the alkenyl phosphate 74 was prepared by trapping the enolate formed on reduction of the enone 73 and was converted into the alkene 75 (7.55). The chemistry therefore provides a method to prepare structurally specihc alkenes. Low-valent titanium (prepared for example by reduction of titanium(III) chloride with potassium metal) is a convenient alternative to lithium or sodium in liquid ammonia or an amine for the reductive cleavage of alkenyl or aryl phosphates. 

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