VIII. Summary
- Page ID
- 24631
Transfer of an electron from samarium(II) iodide to a carbohydrate with an electron-accepting substituent produces a radical anion. Dissociation of this radical anion generates a carbohydrate radical along with an anion derived from the substituent group. A carbohydrate radical formed in this way reacts rapidly with a second molecule of SmI2 to produce an organosamarium compound. This organometallic compound can undergo reactions that include addition to a compound containing a carbonyl group, proton capture, and elimination of a samarium-containing leaving group. In order for a radical formed from reaction of a carbohydrate derivative with SmI2 to avoid immediate reaction with a second molecule of SmI2, a rapid, radical process must intervene. The one of greatest interest is radical cyclization; thus, a carbohydrate derivative that has a properly placed multiple bond and an electron-accepting substituent reacts with samarium(II) iodide to a form radical that cyclizes. Carbohydrates that contain a pair of properly positioned aldehydo or keto groups cyclize to form pinacols. The intermediate in the cyclization step leading to a pinacol is a radical anion. Organochromium complexes form and react in a manner similar to organosamarium compounds.