Complete Facial Selectivity in the Diels–Alder Reaction of a 5-Amino-5-carboxycyclopentadiene Derivative

Copper-Catalyzed Dearomative 1,2-Hydroamination

Catalytic olefin hydroamination reactions are some of the most atom-economical transformations that bridge readily available starting materials-olefins and high-value-added amines. Despite significant advances in this field over the last two decades, the formal hydroamination of nonactivated aromatic compounds remains an unsolved challenge. Herein, we report the extension of olefin hydroamination to aromatic π-systems by using arenophile-mediated dearomatization and Cu-catalysis to perform 1,2-hydroamination on nonactivated arenes. This strategy was applied to a variety of substituted arenes and heteroarenes to provide general access to structurally complex amines. We conducted DFT calculations to inform mechanistic understanding and rationalize unexpected selectivity trends. Furthermore, we developed a practical, scalable desymmetrization to deliver enantioenriched dearomatized products and enable downstream synthetic applications. We ultimately used this dearomative strategy to efficiently synthesize a collection of densely functionalized small molecules.

π-Facial Stereoselectivity in Acyl Nitroso Cycloadditions to 5,5-Unsymmetrically Substituted Cyclopentadienes: Computational Exploration of Origins of Selectivity and the Role of Substituent Conformations on Selectivity

The π-facial selectivity of Diels-Alder cycloadditions of 5-monosubstituted cyclopentadienes is known experimentally and has been extensively studied computationally. Previous studies on 5-monosubstituted cyclopentadienes by the Burnell and Houk groups showed that facial selectivity arises principally from hyperconjugative aromaticity or antiaromaticity of polar groups that cause distortion of the cyclopentadiene; steric effects of nonpolar groups can also be important. We have now explored the stereoselective cycloaddition of 5,5-unsymmetrically substituted cyclopentadienes to an acyl nitroso dienophile reported by Kan and co-workers. Computational studies with M06-2X/6-311+G(d,p) indicate that the stereoselectivity in the cycloadditions of 5,5-unsymmetrically substituted cyclopentadienes is not just a simple combination of effects found for monosubstituted counterparts. Substituent conformations and diene-dienophile steric and electronic interaction effects all influence stereoselectivity. Predictions are made about several as-yet-unstudied cyclopentadiene cycloadditions.

Synthesis of a Bicyclo[2.2.1]heptane Skeleton with Two Oxy-Functionalized Bridgehead Carbons via the Diels-Alder Reaction

We describe a synthetic method for a bicyclo[2.2.1]heptane skeleton with two oxy-functionalized bridgehead carbons. This method involves an intermolecular Diels-Alder reaction using 5,5-disubstituted 1,4-bis(silyloxy)-1,3-cyclopentadienes, the diene structure of which has never been synthesized. Furthermore, the intramolecular Diels-Alder reaction using a diene bearing a dienophile moiety at the C-5 position can provide a tricyclic carbon framework that includes the bicyclo[2.2.1]heptane skeleton. The novel bicyclo[2.2.1]heptane derivatives could be utilized as versatile building blocks for organic synthetic chemistry.

Formation of Aminocyclopentadienes from Silyldihydropyridines: Ring Contractions Driven by Anion Stabilization

Highly functionalized aminocyclopentadienes can be formed through the rearrangement of anions generated from readily prepared 6-silyl-1,2-dihydropyridines by desilylation with fluoride. The scope and generality of the reaction was defined, and diverse transformations were performed on the highly functionalized products. A mechanism and driving force for the rearrangement were identified from experiments and DFT calculations.