Convergent Synthesis of Enantioenriched ortho-Fused Tricyclic Diketones via Catalytic Asymmetric Intramolecular Vinylogous Aldol Condensation.

Herein, we describe a catalytic asymmetric intramolecular vinylogous aldol reaction by taking advantage of dual organocatalysts, which enables convergent synthesis of ortho-fused tricyclic diketones in excellent enantioselectivities and diastereoselectivities. Noteworthy is that the reaction stereoselectively forges three consecutive stereogenic carbon centers including a quaternary one. Density functional theory calculations reveal that the enantioselectivity was facilitated by a transannular hydrogen bonding between the protonated quinuclidine moiety of the chiral aminocatalyst and the diketone fragment of the substrate.

Asymmetric synthesis of 9-alkyl tetrahydroxanthenones via tandem asymmetric Michael/cyclization promoted by chiral phosphoric acid.

A tandem asymmetric Michael-addition/cyclization of cyclic 1,3-dicarbonyl compounds to ß,γ-unsaturated α-ketoesters catalyzed by chiral phosphoric acid is presented. This protocol provides a facile approach for the construction of enantioenriched 9-alkyl tetrahydroxanthenones, an ubiquitous framework found in a number of natural products and pharmaceutical molecules, in high yields with good to high enantioselectivities.