Ryan A. Altman

Palladium-Catalyzed Enantioselective α-Arylation and α-Vinylation of Oxindoles Facilitated by an Axially Chiral P-Stereogenic Ligand

The enantioselective alpha-arylation and alpha-vinylation of oxindoles catalyzed by Pd and a biarylmonophosphine ligand with both axial and phosphorus-based chirogenicity is reported. The resultant quaternary carbon stereocenters are formed in high enantiomeric excess, and the conditions tolerate a range of substitution on both the oxindole and the aryl/vinyl coupling partners.

Orthogonal Pd- and Cu-based catalyst systems for C- and N-arylation of oxindoles.

In the cross-coupling reactions of unprotected oxindoles with aryl halides, Pd- and Cu-based catalyst systems displayed orthogonal chemoselectivity. A Pd-dialkylbiarylphosphine-based catalyst system chemoselectively arylated oxindole at the 3 position, while arylation occurred exclusively at the nitrogen using a Cu-diamine-based catalyst system. Computational examination of the relevant L1Pd(Ar)(oxindolate) and diamine-Cu(oxindolate) species was performed to gain mechanistic insight into the controlling features of the observed chemoselectivity.

Pyrrole-2-carboxylic Acid as a Ligand for the Cu-Catalyzed Reactions of Primary Anilines with Aryl Halides

Pyrrole 2-carboxylic acid (L5) was found to be an effective ligand for the Cu-catalyzed monoarylation of anilines with aryl iodides and bromides. Under the reported conditions (10% CuI/20% L5/DMSO/K3PO 4/80-100 degrees C/20-24 h), a variety of useful functional groups were tolerated, and moderate to good yields of the diaryl amine products were obtained.

Ligand‐Controlled Regiodivergent Palladium‐Catalyzed Decarboxylative Allylation Reaction to Access α,α‐Difluoroketones

α,α-Difluoroketones possess unique physicochemical properties that are useful for developing therapeutics and probes for chemical biology. To access the α-allyl-α,α-difluoroketone substructure, complementary palladium-catalyzed decarboxylative allylation reactions were developed to provide linear and branched α-allyl-α,α-difluoroketones. For these orthogonal processes, the fluorination pattern of the substrate enabled the ligands to dictate the regioselectivity of the transformations.

Total synthesis of (+)-nankakurines A and B and (±)-5-epi-nankakurine A.

The first total syntheses of the Lycopodium alkaloids (+)-nankakurine A (2), (+)-nankakurine B (3), and the originally purported structure 1 of nankakurine A were accomplished. The syntheses of 2 and 3 feature a demanding intramolecular azomethine imine cycloaddition as the key step for generating the octahydro-3,5-ethanoquinoline moiety and installing the correct relative configuration at the spiropiperidine ring juncture. The cyclization precursor was prepared from octahydronaphthalene ketone 50, which was assembled from enone (+)-9 and diene 48 by a cationic Diels-Alder reaction. The Diels-Alder reactants were synthesized from 5-hexyn-1-ol (16) and (+)-pulegone (49), respectively. The tetracyclic ring system of 1 was generated using an unprecedented nitrogen-terminated aza-Prins cyclization cascade. The enantioselective total syntheses of (+)-nankakurine A (2) and (+)-nankakurine B (3) establish the relative and absolute configuration of these alkaloids and are sufficiently concise that substantial quantities of 2 and 3 were prepared for biological studies. (+)-Nankakurine A and (+)-nankakurine B showed no effect on neurite outgrowth in rat hippocampal H-19 cells over a concentration range of 0.3-10 μM.

Pd-catalyzed Suzuki–Miyaura reactions of aryl halides using bulky biarylmonophosphine ligands

The following protocol describes the application of a highly active Pd-based catalyst system in the Suzuki–Miyaura cross-coupling reaction of arylboronic acids with aryl chlorides to provide biaryl compounds. The general procedure includes a detailed description of an appropriate reaction setup, two methods for assaying the crude reaction mixture (GC and TLC) and a procedure for the isolation, purification and characterization of the anticipated product. Reagents and catalyst precursors can be manipulated in the air; however, the cross-coupling reactions must be performed in an inert atmosphere. Two Suzuki–Miyaura reactions are included in the text as representative examples of these procedures. Although the reactions can proceed in less than 5 min, the protocols, including workup, generally take 6–30 h to be completed.

Metal-Free Trifluoromethylation of Aromatic and Heteroaromatic Aldehydes and Ketones

The ability to convert simple and common substrates into fluoroalkyl derivatives under mild conditions remains an important goal for medicinal and agricultural chemists. One representative example of a desirable transformation involves the conversion of aromatic and heteroaromatic ketones and aldehydes into aryl and heteroaryl β,β,β-trifluoroethylarenes and -heteroarenes. The traditional approach for this net transformation involves stoichiometric metals and/or multistep reaction sequences that consume excessive time, material, and labor resources while providing low yields of products. To complement these traditional strategies, we report a one-pot metal-free decarboxylative procedure for accessing β,β,β-trifluoroethylarenes and -heteroarenes from readily available ketones and aldehydes. This method features several benefits, including ease of operation, readily available reagents, mild reaction conditions, high functional-group compatibility, and scalability.

Preparation of Fluoroalkenes via the Shapiro Reaction: Direct Access to Fluorinated Peptidomimetics

Fluoroalkenes represent a useful class of peptidomimetics with distinct biophysical properties. Current preparations of this functional group commonly provide mixtures of E- or Z-fluoroalkene diastereomers, and/or mixtures of nonfluorinated products. To directly access fluoroalkenes in good stereoselectivity, a Shapiro fluorination reaction was developed. Fluoroalkene products were accessed in one- or two-step sequences from widely available ketones. This strategy should be useful for the preparation of fluorinated analogs of peptide-based therapeutics, many of which would be challenging to prepare by alternate strategies.

Cu-catalyzed Goldberg and Ullmann reactions of aryl halides using chelating N- and O-based ligands

The following protocol can be applied in the selective cross-coupling reaction of an amine with an aryl iodide or bromide using a copper (Cu)-based catalyst to provide the corresponding N-aryl amine. The general procedure described in this text includes a detailed description of an appropriate reaction setup, two methods for assaying the crude reaction mixture (gas chromatography and thin layer chromatography) and a procedure for the isolation, purification and characterization of the anticipated product. Manipulation of the reagents can be done in the air, without the use of a glovebox; however, the cross-coupling reactions must be performed in a sealed reactor under an inert atmosphere. Three C–N bond-forming reactions are included in the protocol as representative examples of this procedure. Although the reactions can proceed in <1 h, the protocols, including workup, generally take 6–30 h to complete.

Copper-catalyzed decarboxylative trifluoromethylation of allylic bromodifluoroacetates.

The development of new synthetic fluorination reactions has important implications in medicinal, agricultural, and materials chemistries. Given the prevalence and accessibility of alcohols, methods to convert alcohols to trifluoromethanes are desirable. However, this transformation typically requires four-step processes, specialty chemicals, and/or stoichiometric metals to access the trifluoromethyl-containing product. A two-step copper-catalyzed decarboxylative protocol for converting allylic alcohols to trifluoromethanes is reported. Preliminary mechanistic studies distinguish this reaction from previously reported Cu-mediated reactions.