Triethylborane-Induced Intermolecular Radical Addition to Ketimines

Indium(iii)-catalyzed efficient synthesis of 3-arylhydrazonoindolin-2-ones and their fluorescent metal sensing studies

In(iii)-catalyzed strategy for the preparation of 3-arylhydrazonoindolin-2-ones from 3-diazoindoles is developed and used for Fe3+ and Hg2+ ion sensing.

Visible-Light-Mediated Carbonyl Alkylative Amination to All-Alkyl α-Tertiary Amino Acid Derivatives

The all-alkyl α-tertiary amino acid scaffold represents an important structural feature in many biologically and pharmaceutically relevant molecules. Syntheses of this class of molecule, however, often involve multiple steps and require activating auxiliary groups on the nitrogen atom or tailored building blocks. Here, we report a straightforward, single-step, and modular methodology for the synthesis of all-alkyl α-tertiary amino esters. This new strategy uses visible light and a silane reductant to bring about a carbonyl alkylative amination reaction that combines a wide range of primary amines, α-ketoesters, and alkyl iodides to form functionally diverse all-alkyl α-tertiary amino esters. Brønsted acid-mediated in situ condensation of primary amine and α-ketoester delivers the corresponding ketiminium species, which undergoes rapid 1,2-addition of an alkyl radical (generated from an alkyl iodide by the action of visible light and silane reductant) to form an aminium radical cation. Upon a polarity-matched and irreversible hydrogen atom transfer from electron rich silane, the electrophilic aminium radical cation is converted to an all-alkyl α-tertiary amino ester product. The benign nature of this process allows for broad scope in all three components and generates structurally and functionally diverse suite of α-tertiary amino esters that will likely have widespread use in academic and industrial settings.

Radical "On Water" Addition to the C═N Bond of Hydrazones: A Synthesis of Isoindolinone Derivatives

A radical "on water" addition to the C═N bond of hydrazones has been described. Hydrazone, diphenylsilane, alkyl iodide, and triethylborane afforded the corresponding addition products "on water" in good yields. A significant solvent effect was observed from the water. The developed protocol can be applied to the synthesis of 3-substituted isoindolinone derivatives. Moreover, the process offers environmentally benign tin-free radical reaction conditions.

Control of asymmetry in the radical addition approach to chiral amine synthesis

The state-of-the-science in asymmetric free radical additions to imino compounds is presented, beginning with an overview of methods involving stereocontrol by various chiral auxiliary approaches. Chiral N-acylhydrazones are discussed with respect to their use as radical acceptors for Mn-mediated intermolecular additions, from design to scope surveys to applications to biologically active targets. A variety of aldehydes and ketones serve as viable precursors for the chiral hydrazones, and a variety of alkyl iodides may be employed as radical precursors, as discussed in a critical review of the functional group compatibility of the reaction. Applications to amino acid and alkaloid synthesis are presented to illustrate the synthetic potential of these versatile stereocontrolled carbon-carbon bond construction reactions. Asymmetric catalysis is discussed, from seminal work on the stereocontrol of radical addition to imino compounds by non-covalent interactions with stoichiometric amounts of catalysts, to more recent examples demonstrating catalyst turnover.

Asymmetric construction of quaternary stereocenters by direct organocatalytic amination of 3-substituted oxindoles

Quinidine derivative (QD)(2)PYR was found to catalyze the asymmetric direct amination of unprotected prochiral 3-oxindole with DIAD to construct quaternary stereocenters at the C3 position with excellent enantioselectivity.

Highly enantioselective and organocatalytic alpha-amination of 2-oxindoles

An effective method for the asymmetric synthesis of 3-amino-2-oxindoles was developed. The tetrasubstituted chiral carbon center was generated by asymmetric amination of N-unprotected 2-oxindoles with azodicarboxylate catalyzed by commercial biscinchona alkaloids in good to excellent yields with high enantioselectivities.

Reactive Ketimino Radical Acceptors: Intermolecular Alkyl Radical Addition to Imines with a Phenolic Hydroxyl Group

Intermolecular carbon radical addition to the carbon-nitrogen double bond of ketimines was studied. In the study on the reactivity of various aldimines, we found that the aldimine 7 having a phenolic hydroxyl group shows an excellent reactivity toward nucleophilic carbon radicals. A remarkable effect of phenolic hydroxyl group is assumed to be the stabilization of intermediate aminyl radical provided by a hydroxyl group. The screening of reactive ketimino acceptors showed that ketimines 15, 17, and 19 having a phenolic hydroxyl group exhibit excellent reactivities. The radical addition to ketimines 15, 17, and 19 took place regioselectively at the imino carbon to give the C-alkylated products without the formation of N-alkylated products. Enantioselective ethyl radical addition to ketimine 15 using chiral box ligand and Zn(OTf)2 gave the diethylated product 30 in 80% ee.