PINACOL COUPLING OF ALIPHATIC-ALDEHYDES PROMOTED BY NIOBIUM-(III) REAGENT

NbCl3 (DME) was found io be a useful reagent for tile intermolecular p inacol coupling of aliphatic aldehydes. The high anti diastereoselecti vity of this reaction (dl/meso greater than or equal to 9/l) did nor d epend on the variation in the aldehyde alkyl chain. With respect to in tramolecular pinacolization, the loss of the stereoselectivity observe d is consistent with the mechanism involving an insertion of the era-g roup into the metal-carbon bond of the intermediate niobiooxirane.