Asymmetric Formal trans-Dihydroxylation and trans-Aminohydroxylation of α,β-Unsaturated Aldehydes via an Organocatalytic Reaction Cascade

This study demonstrates the first formal asymmetric trans-dihydroxylation and trans-anninohydroxylation of alpha,beta-unsaturated aldehydes in an organocatalytic multibond forming one-pot reaction cascade This efficient process converts alpha,beta-unsaturated aldehydes into optically active trans-2,3-dihydroxyaldehydes and trans-3-amino-2-hydroxyaldehydes with the aldehyde moiety protected as an acetal. The elaborated one-pot protocol proceeds via the formation of 2,3-epoxy and 2,3-azindine aldehyde intermediates, which subsequently participate in a novel NaOMe-initiated rearrangement reaction leading to the formation of acetal protected trans-2,3-dihydroxyaldehydes and trans-3-amino-2-hydroxyaldehydes in a highly stereoselective manner Advantageously, this multibond forming reaction cascade can be performed one-pot, thereby minimizing the number of manual operations and purification procedures required to obtain the products Additionally, for the purpose of trans-aminohydroxylation of the alpha,beta-unsaturated aldehydes, a new enantioselective azindination protocol using 4-methyl-N-(tosyloxy)benzenesulfonamide as the nitrogen source has been developed The mechanism of the formal trans-dihydroxylation and trans-aminohydroxylation of alpha,beta-unsaturated aldehydes is elucidated by various investigations including isotopic labeling studies Finally, the products obtained were applied in the synthesis of numerous important molecules