Silver(I)‐Catalyzed Enantioselective [3+2]‐Cycloaddition Reaction of α‐Silylimines: A Facile Route to Quaternary‐Carbon‐Rich Scaffolds

Abstract

A silver-catalyzed highly enantioselective 1,3-dipolar cycloaddition reaction of α-silylimines with pyrone-based trisubstituted olefins was developed affording bi- and tricyclic α-quaternary-carbon-rich pyrano-pyrrolidines in excellent yields. The tricyclic benzopyrone adducts thus obtained were efficiently transformed into highly complex tetracyclic scaffolds supporting four consecutive stereogenic centers with three quaternary carbons.

A Scaffold‐Diversity Synthesis of Biologically Intriguing Cyclic Sulfonamides

“…Interestingly, reactions of 7 derived dipole performed better with aryl or alkyl ketimine 1 than with aldimine ( 1 , R 1 =H) or iminoester ( 1 , R 1 =CO 2 Et, Scheme ). Notably, α‐silyl imines ( 9 ) have rarely been explored in cycloaddition chemistry and are interesting substrates for generating small molecules embodying quaternary centers and complex stereochemical frameworks . Another reaction screening revealed that catalytic AgOAc and phosphine complex in acetonitrile could transform 1‐CO 2 Et with 9 into syn ‐imidazolidine 10 (d.r.=87:13) as major adduct that bear two consecutive quaternary stereocenters (Table S1 in Supporting information).…”

Access to Chromenopyrrolidines Enabled by Organophotocatalyzed [2 + 2 + 1] Annulation of Chromones with N-Arylglycines

“…For example, compound 1' exhibits significant inhibition against 5-lipoxygenase in the cell-free assay, and spiropyrrolidines 2' – 6' were found to be cytotoxic against K562 cells, while fluorochromenopyrrolidines 7' –8' can be used for treating erectile disorders (Scheme a) . The existing approaches toward chromenopyrrolidines routinely rely on the [3 + 2] cycloaddition of chromones or their derivatives with in situ -generated azomethine ylides (Scheme b) via heating, acid, transition-metal, or Lewis base catalysis in which highly active carbonyl compounds, such as formaldehyde or α-activated ketones, were required. On the other hand, even though chromones were extensively utilized as reactants in many cases of photocatalysis, they were merely used as Giese-type addition acceptors to deliver 2-functionalized chroman-4-ones as the final products, while photocatalyzed annulation of chromones was rarely disclosed .…”

Enantioselective Mukaiyama–Michael Reaction of Cyclic α-Alkylidene β-Keto Phosphine Oxide and Phosphonate and Asymmetric Synthesis of (R)-Homosarkomycin

“…Alkenes bearing two electron-withdrawing groups have been widely used as electrophiles in a variety of transformations including catalytic asymmetric reactions such as cycloadditions, Michael reactions, and Friedel–Crafts reactions due to their electron-deficient properties. Owing to their greater reactivity, alkenes bearing two electron-withdrawing groups have been employed as key intermediates in natural product synthesis .…”