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α-Iminol rearrangements catalyzed by silica gel and montmorillonite K 10. a) For 102a (102 with R = Ph), silica gel and montmorillonite K 10 gave ≥95% yields, while Brønsted acids, other Lewis acids, and NaOEt generally performed much more poorly. b) Electron-rich R groups rearrange efficiently in the presence of silica gel but not the electron-deficient p-trifluoromethylphenyl derivative. c) In the presence of silica gel or montmorillonite K 10, TBS-protected 101 is converted to 102 without any side products, but when sulfuric acid is used, only the deprotected product 103 is detected. d) Silica gel-catalyzed rearrangement of 104 provided 105, an analogue of the anesthetic ketamine (106).
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In the presence of a suitable acid or base, α-hydroxyaldehydes, ketones, and imines can undergo isomerization that features the 1,2-shift of an alkyl or aryl group. In the process, the hydroxy group is converted to a carbonyl and the aldehyde/ketone or imine is converted to an alcohol or amine. Such α-ketol/α-iminol rearrangements are used in a wid...
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Citations
A carbonyl‐assisted asymmetric 1,2‐migratory allylation through in situ generation of vicinal tetrasubstituted stereocenters is reported to access enantiopure α‐amino ketones, and amino‐alcohols with excellent yields and diastereoselectivities. In a remarkable divergence, despite having higher steric hindrance, the allylation exclusively occurs on ketones over imines in the first step, followed by a face‐selective 1,2‐allyl transfer, thus highlighting an exciting interplay between two distinct electrophiles. The methodology distinguishes itself through its adaptability to gram‐scale synthesis, showcasing broad functional group tolerance, and stereodivergence. The density functional theory (DFT) analysis elucidates a deeper understanding of its selectivity and mechanistic framework. Highlighting its transformative potential, the total synthesis of hapalindole alkaloids were adeptly achieved.
A carbonyl‐assisted asymmetric 1,2‐migratory allylation through in situ generation of vicinal tetrasubstituted stereocenters is reported to access enantiopure α‐amino ketones and amino alcohols with excellent yields and diastereoselectivities. In a remarkable divergence, despite higher steric hindrance, the allylation exclusively occurs on ketones over imines in the first step, followed by a face‐selective 1,2‐allyl transfer, thus highlighting an exciting interplay between two distinct electrophiles. The methodology distinguishes itself through its adaptability to gram‐scale synthesis, showcasing broad functional‐group tolerance and stereodivergence. Density functional theory (DFT) analysis led to a deeper understanding of its selectivity and mechanistic framework. Highlighting its transformative potential, the method was applied to the total synthesis of hapalindole alkaloids.
Reactions capable of transposing the oxidation levels of adjacent carbon atoms enable rapid and fundamental alteration of a molecule’s reactivity. Herein, we report the 1,2-transposition of the carbon atom oxidation level in cyclic and acyclic tertiary amides, resulting in the one-pot synthesis of 1,2- and 1,3-oxygenated tertiary amines. This oxidation level transfer was facilitated by the careful orchestration of an iridium-catalyzed reduction with the functionalization of transiently formed enamine intermediates. A novel 1,2-carbonyl transposition is described, and the breadth of this redox transposition strategy has been further explored by the development of aminoalcohol and enaminone syntheses. The diverse β-functionalized amine products were shown to be multifaceted and valuable synthetic intermediates, accessing challenging biologically relevant motifs.
The asymmetric total synthesis of (-)-retigeranic acid A was described, which relies on a crucial reductive skeletal rearrangement cascade for the controllable assembly of diverse angular triquinane subunits. Taken together with an intramolecular Michael/aldol cyclization, an ODI-[5 + 2] cycloaddition/pinacol rearrangement cascade, a Wolff ring contraction and a stereoselective HAT reduction, our synthetic approach has enabled the access to (-)-retigeranic acid A in a concise and practical manner.
Reactions capable of transposing the oxidation levels of adjacent carbon atoms in organic molecules enable rapid and fundamental alteration of a molecule’s reactivity. Herein, we report the 1,2-transposition of carbon atom oxidation level in cyclic and acyclic tertiary amides, resulting in the one-pot synthesis of 1,2- and 1,3-oxygenated tertiary amines. This oxidation level transfer was facilitated by the careful orchestration of an iridium-catalyzed reduction with the functionalization of transiently-formed enamine intermediates. Remarkably, a novel 1,2-carbonyl transposition was observed when the commercial oxidant mCPBA was selected as the coupling partner. The scope of this transformation and the breadth of this redox transposition strategy has been explored and the diverse β-functionalized amine products were shown to be multi-faceted and valuable synthetic intermediates, accessing challenging biologically-relevant motifs.
