text: Halonium ylides can be prepared from allyl halides and metal carbenoids. After a [2,3]-rearrangement, a homoallylhalide is obtained.
  The active form of Tebbe's reagent is often considered a titanium ylide. Like the Wittig reagent, it is able to replace the oxygen atom on carbonyl groups with a methylene group. Compared with the Wittig reagent, it has more functional group tolerance.