Niobium(V) chloride-mediated allylation of aldehydes. Scope and stereoselectivity

Niobium chloride promoted the addition of allylstannanes to aromatic and aliphatic aldehydes. Excellent syn diastereoselectivity was obtained in the addition of E-cinnamylstannane to benzaldehyde (49:1). In the addition of allylstannane to racemic 2-phenylpropionaldehyde, syn diastereoselection (Cram–anti-Cram=3:1) was observed. The same level of diastereoselection was achieved in the reaction between crotylstannane and benzaldehyde.