Oxidative cleavage of 1,2-diols to give aldehydes/ketones
Description: Treatment of vicinal diols (1,2-diols) with an oxidant such as NaIO4, HIO4, or Pb(OAc)4 cleaves C–C bonds and forms carbonyl compounds.
Notes: For our purposes NaIO4, HIO4, or Pb(OAc)4 are essentially equivalent for this purpose.
Notes: Note that whether or not the carbonyl compound product is an aldehyde or ketone depends on the substitution pattern of the alcohol. Secondary alcohols are become aldehydes, tertiary alcohols become ketones, and primary alcohols become formaldehyde.
Mechanism: Four boring steps precede the important C–C cleavage step (Step 5). Attack of oxygen on iodine (Step 1, arrows A and B) is followed by a proton transfer (Step 2, arrows C and D). This is followed by a second iodine-oxygen bond being formed (Step 3, arrows E and F). and a second proton transfer (Step 4, arrows Ga nd H). Finally iodine is reduced from I(VII) to I(V) with accompanying C–O π bond formation and C–C bond cleavage to give the two carbonyls along with iodine (V).
Notes: The mechanism involving NaIO4 and Pb(OAc)4 are very similar.