Chromium(II)-catalyzed diastereoselective pinacol type cross coupling between alpha,beta-unsaturated carbonyl compounds and aliphatic aldehydes

Using only 10 mol% of CrCl2 as catalyst, acroleins and α,β-unsaturated ketones were coupled with aliphatic aldehydes to obtain substituted 1,2-diols using manganese powder as reducing agent and TMS-Cl as scavenger. Diastereoselectivities depend on the substituents especially on R1 of the unsaturated carbonyl compound. Formation of the syn-diols is preferred with sterically demanding R1, the anti-diols are obtained with smaller substituents