Water-compatible one-pot organocatalytic asymmetric synthesis of cyclic nitrones. Application in intramolecular 1,3-dipolar cycloadditions

Enantioselective Total Synthesis of (+)-Stephadiamine

An asymmetric synthesis of (+)-stephadiamine has been accomplished featuring (a) an enantioselective dearomatizative Michael addition to generate a quaternary stereocenter; (b) a domino sequence involving reductive generation of nitrone from γ-nitro ketone followed by a highly regio- and diastereo-selective intramolecular [3 + 2] cycloaddition to construct the aza[4,3,3]propellane core with concurrent generation of two quaternary stereocenters and two functional groups ready for subsequent transformations; (c) the Curtius rearrangement of the sensitive α,α-disubstituted malonic acid mono ester for the installation of α,α-disubstituted amino ester moiety; (d) a benzylic C-H oxidation under photoredox catalytic conditions; and (e) a highly diastereoselective ketone reduction affording δ-hydroxyester preorganized for lactonization.

Asymmetric Synthesis of Fused Tetrahydroquinolines via Intra­molecular Aza-Diels–Alder Reaction of ortho-Quinone Methide Imines

Aza-Diels–Alder reactions are straightforward processes for the construction of N-heterocycles, featuring inherent atom-economy and stereospecificity. Intramolecular strategies allow the formation of bicyclic core structures with up to three stereocenters within a single step. Herein, this concept is combined with the chemistry of chiral Brønsted acid bound ortho-quinone methide imines to generate a range of interesting fused tetrahydroquinolines in a diastereo- and enantioselective­ manner.

Enantioselective Synthesis of Cyclic Nitrones by Chemoselective Intramolecular Allylic Alkylation of Oximes

The enantio- and chemoselective iridium-catalyzed N-allylation of oximes is described for the first time. Intramolecular kinetic resolution provides access to cyclic nitrones and enantioenriched aliphatic allylic alcohols. Salient features of this transformation are its ability to employ E/Z-isomeric mixtures of oxime starting materials convergently and high functional group tolerance. The implementation of N-allylation/1,3-dipolar cycloaddition reaction sequences furnishes tricyclic isoxazolidines in highly enantio- and diastereoselective fashion. The synthetic utility of the approach is demonstrated by the efficient, formal synthesis of the marine natural product (+)-halichlorine.

Synthesis and Transformations of Nitrones for Organic Synthesis

Nitrones are important compounds and are highly useful in many aspects. The first part describes the methods for synthesis of nitrones, which are useful and environmentally friendly. Catalytic oxidations, condensations, and other useful reactions are described. The nitrones thus obtained are key intermediates for the synthesis of biologically important nitrogen compounds. The second part describes the fundamental transformations of nitrones, which will provide the strategies and means for the construction of nitrogen compounds. The reactions with nucleophiles or radicals, C-H functionalization, and various addition reactions are described. The last reactions are particularly important for highly selective carbon-carbon bond formations. 1,3-Dipolar cycloaddition reactions are excluded because the size of the review is limited and excellent reviews have been published in Chemical Reviews.

Total Synthesis of (+)-SCH 351448: Efficiency via Chemoselectivity and Redox-Economy Powered by Metal Catalysis

The polyketide natural product (+)-SCH 351448, a macrodiolide ionophore bearing 14 stereogenic centers, is prepared in 14 steps (LLS). In eight prior syntheses, 22-32 steps were required. Multiple chemoselective and redox-economic functional group interconversions collectively contribute to a step-change in efficiency.