Preparation of a Chiral Building Block by an Organocatalytic Asymmetric Intramolecular Michael Reaction

The preparation of a chiral building block, including a stereodiad consisting of two tertiary stereogenic centers, by a highly enantioselective organocatalytic intramolecular Michael reaction is described. The use of a chiral secondary-amine-bearing thiourea substituted with a para-nitrophenyl group in the presence of benzoic acid is key to preparing the chiral building block in high yield and excellent enantioselectivity. The prepared chiral building block has both aldehyde and nitro groups, allowing a variety of functional-group transformations necessary for the total synthesis of atisane-type terpenoids.