Aminocatalytic Synthesis of Uracil Derivatives Bearing a Bicyclo[2.2.2]octane Scaffold via a Doubly Cycloadditive Reaction Cascade

Shaping Chirality via Stereoselective, Organocatalytic [4+2] Cycloadditions involving Heterocyclic ortho-Quinodimethanes

Polycyclic compounds bearing a complex heterocyclic core such as an aromatic heterocycle "fused" with one or more functionalized rings, are widespread leading molecules in the domain of synthetic organic chemistry and pharmaceuticals. Although many synthetic methodologies have been devised to access achiral, fused heteroaromatic scaffolds, or related chiral variants adorned with out-of-cycle stereogenic elements, equally efficient strategies to afford chiral heterocycles featuring in-cycle stereocenters, exist to a lesser extent and presently represent a growing field of investigation. The mild, organocatalytic generation of elusive ortho-quinodimethane intermediates (oQDMs), derived from suitable heteroaromatic carbonyl- or carbonyl-like pronucleophiles has recently proved successful in the synthesis of such peculiar chiral architectures via stereoselective [4+2] cycloadditions. This review provides an overview of the most important advances attained in this field over the last decade.

N-Heterocyclic Carbene-Catalyzed Enantioselective Synthesis of Carbocycle-Fused Uracils via Formal [4 + 2] Annulation/Lactone Formation/Decarboxylation Cascade

An unprecedented organocatalytic asymmetric construction of novel six-membered carbocycle fused uracils has been demonstrated by the reaction of the remotely enolizable 6-methyluracil-5-carbaldehydes with 2-bromoenals. The reaction involves an N-heterocyclic carbene-catalyzed formal [4 + 2] annulation of o-quinodimethane (oQDM) dienolates with α,β-unsaturated acylazoliums, followed by a cascade lactone formation/decarboxylation process. This protocol unlocks a new platform to access enantioenriched carbocycle-fused uracils.

Asymmetric Dearomative (3+2)-Cycloaddition Involving Nitro-Substituted Benzoheteroarenes under H-Bonding Catalysis

In our studies, the organocatalytic 1,3-dipolar cycloaddition between 2-nitrobenzofurans or 2-nitrobenzothiophene and N-2,2,2-trifluoroethyl-substituted isatin imines has been developed. The reaction has been realized by employing bifunctional organocatalysis, with the use of squaramide derivative being crucial for the stereochemical efficiency of the process. The usefulness of the cycloadducts obtained has been confirmed in selected transformations, including aromative and non-aromative removal of the nitro group.

1,3-Cyclohexadien-1-Als: Synthesis, Reactivity and Bioactivities

In synthetic organic chemistry, there are very useful basic compounds known as building blocks. One of the main reactions wherein they are applied for the synthesis of complex molecules is the Diels-Alder cycloaddition. This reaction is between a diene and a dienophile. Among the most important dienes are the cyclic dienes, as they facilitate the reaction. This review considers the synthesis and reactivity of one of these dienes with special characteristics-it is cyclic and has an electron withdrawing group. This building block has been used for the synthesis of biologically active compounds and is present in natural compounds with interesting properties.