V. Reaction of Samarium(II) Iodide with Aldehydes and Ketones
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Reaction of an aldehyde or ketone with samarium(II) iodide produces a samarium ketyl.26–39 These ketyls add intramolecularly to appropriately positioned carbon–carbon25–33 (Scheme 10)26 and carbon–nitrogen34–37 (eq 10)34 double bonds. Such reactions are reminiscent of the addition of typical carbon-centered radicals to multiple bonds.
When samarium(II) iodide reacts with compounds containing two aldehydo groups, the first is converted into a samarium ketyl that then adds to the second. This addition depends upon proper separation between the reacting groups;40–53 accordingly, pinacols with five-membered40,49‑53 (eq 11)40 and six-membered41–48 (eq 12)41 rings form easily. It is not necessary for both interacting groups in a molecule to be aldehydo groups; pinacols also arise when one49–52 (eq 13, R = H)49 or both (eq 13, R = CH2SiMe2C6H5)53 are keto groups. Complexation of the ketyl and carbonyl oxygen atoms with SmI2 forces a cis relation between the hydroxyl groups in the products (Scheme 11).42 Pinacol formation and other reactions of aldehydes and ketones with samarium(II) iodide is revisited in Chapter 20, where a broader discussion of the interaction of SmI2 with carbohydrate derivatives takes place.