2-Nitroallyl carbonate-based green bifunctional reagents for catalytic asymmetric annulation reactions.

2-Nitroallylic carbonates, a new class of "green" 1,3-bielectrophilic reagents for organic synthesis and catalysis, have been prepared. The bifunctional tertiary amine-catalyzed asymmetric [3 + 3] annulations of cyclic enols with these reagents occur much faster than corresponding reactions with 2-nitroallylic esters and produce no acidic by-products poisoning the catalyst. Furthermore, 2-nitroallylic carbonates enable highly enantioselective one-pot synthesis of a variety of fused dihydropyrane derivatives from available precursors bearing pharmacophoric fragments.

C-Symmetric Chiral Squaramide, Recyclable Organocatalyst for Asymmetric Michael Reactions.

A very simple and highly efficient C-symmetric tertiary amine-squaramide organocatalyst for asymmetric Michael reactions has been elaborated. In the presence of only 1 mol % of this catalyst, kojic acid derivatives and β-dicarbonyl compounds reacted with nitroolefins, affording the corresponding adducts in a nearly quantitative yield with an enantioselectivity up to 99% ee. The kojic acid-derived adducts could be efficiently produced under "green" conditions (in 96% EtOH or pure water).

Asymmetric Michael addition between kojic acid derivatives and unsaturated ketoesters promoted by C-symmetric organocatalysts.

An efficient sterically hindered C2-symmetric bifunctional tertiary amine-squaramide organocatalyst for the asymmetric Michael addition/hemiketalization domino reaction of kojic acid derivatives with β,γ-unsaturated α-ketoesters has been designed. Pharmacology-relevant functionalized 2,3,4,8-tetrahydropyrano[3,2-b]pyran derivatives were produced over the catalyst in as low as 1 mol% with up to 99% yield and 99% ee. The procedure is at least 30-fold scalable and the catalyst is readily reusable in the catalytic reaction via acid-base extraction.