Total Synthesis of Immunosuppressive Mycestericin E and G Enabled by a Highly Stereoselective Nitroso-Ene Cyclization

This report describes a streamlined synthesis of immunosuppressive mycestericin E and G through a highly stereoselective nitroso-ene cyclization in 11-12 steps using readily available materials. The stereochemical outcome in the formation of a Nα-quaternary stereogenic center is rationalized by a trajectory based on the polar diradical intermediate and subsequent hydrogen transfer. Julia olefination offers a facile chain elongation method that presents a viable strategy for structural derivatization in future medicinal applications.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C-N bond-forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Regio- and enantioselective amination of acyclic branched α-alkynyl ketones: asymmetric construction of N-containing quaternary stereocenters

Direct regio- and enantioselective amination of acyclic α-branched ketones enabled by the α-alkynyl group.

Enantioselective α-Amination of Acyclic 1,3-Dicarbonyls Catalyzed by N-Heterocyclic Carbene

Herein, we describe a method for the catalytic enantioselective α-amination of α-substituted acyclic 1,3-ketoamides and 1,3-amidoesters that affords the products possessing N-substituted quaternary stereocenters with a chiral N-heterocyclic carbene (NHC). The reaction is based on the utilization of an intrinsic Brønsted base characteristic of NHC that enables the catalytic formation of a chiral ion pair comprising the enolate and the azolium ion. A series of challenging open-chain α-substituted 1,3-dicarbonyls are aminated via this method with ee's of ≤99%.

Synthesis and anticancer profile of novel sphingoid base-like compounds with a quaternary stereocentre

The synthesis of novel sphingoid base-like compounds with a quaternary stereocentre was achieved in a sequence featuring [3,3]-sigmatropic rearrangements and olefin cross-metathesis transformation as the key reaction steps, which were accompanied by the rational selection of suitable functional group transformations. The stereochemistry of the desired tetra-substituted carbon bearing nitrogen functionality was determined via NOESY experiments of the advanced oxazolidine-2-thiones. Cell viability experiments revealed significant antiproliferative/cytotoxic activity of the target compounds 7, ent-7 and 29 against the Jurkat cell line, with the IC₅₀ values of 6.6 μM, 5.6 μM and 6.1 μM, respectively.

Construction of Quaternary Carbon Stereocenter of α-Tertiary Amine through Remote C-H Functionalization of Tris Derivatives: Enantioselective Total Synthesis of Myriocin

We describe the development of a strategy for the construction of the quaternary carbon stereocenter of α-tertiary amines. This strategy highlights a site-selective C-H functionalization involving an alkoxy-radical-triggered 1,5-hydrogen transfer (1,5-HAT) reaction of a conformationally fixed spiro-compound derived from trishydroxymethylaminomethane (Tris). The utilization of this strategy enabled an enantioselective total synthesis of myriocin, a naturally occurring sphingosine analog that displays potent immunosuppressive activity.

Applications of γ,δ-Unsaturated Ketones Synthesized by Copper-Catalyzed Cascade Addition of Vinyl Grignard Reagents to Esters

γ,δ-Unsaturated ketones, so-called homoallylic ketones, have served as versatile building blocks for the synthesis of a variety of heterocycles, carbocycles, natural products, and reactive intermediates. Procured by a variety of processes, including conjugate addition of vinyl organometallic reagents to unsaturated ketones, allylation of silyl enol ethers, and rearrangements, homoallylic ketones are often synthesized by step-intensive methods. The cascade addition of 2 equiv of vinyl Grignard reagent to a carboxylate was reported by the Lubell laboratory in 2003 to give effective access to homoallylic ketones from a variety of aromatic, aliphatic, and α-amino methyl esters. Employing readily accessible vinyl magnesium halides in the presence of a catalytic amount of copper salt, this cascade reaction provides high yields of homoallylic ketones with minimal side product by a process featuring the assembly and collapse of a tetrahedral intermediate with expulsion of alkoxide ion, followed by conjugate addition to the resulting enone. Application of the cascade reaction to the synthesis of various homoallylic ketones has provided versatile building blocks for the synthesis of targets for different applications. For example, by employing (hetero)aryl di- and tricarboxylates as precursors, copper-catalyzed cascade additions have provided donor-acceptor and star-shaped monomers for optical-electronic materials. Amino ester starting materials have given homoallylic ketones for the synthesis of various peptidomimetics, including heteroarylalanines, hydroxyethylene isoesters, and diazepinone turn mimics. Moreover, anthranilate has served as building block to prepare various pyrrole, quinoline, benzodiazepine, and benzotriazepine heterocyles. In addition, cascade additions on hydroxyprolinates have given access to bipyrrole precursors of the prodigiosin family of natural products. In the interest to highlight the utility of the copper-catalyzed cascade addition of vinyl Grignard reagents to carboxylates, this Account provides details on the broad scope of substrates that deliver homoallylic ketone products as well as an overview of the wide range of applications in which this method may impact including materials and peptide science, heterocycle and natural product synthesis, and medicinal chemistry.

Catalytic asymmetric α-amination of β-keto esters and β-keto amides with a chiral N,N′-dioxide–copper(i) complex

The highly efficient asymmetric α-amination of β-keto esters and β-keto amides was realized by using a chiral N,N′-dioxide/Cu(i) complex. Under mild reaction conditions, a series of chiral α-amino dicarbonyl compounds were obtained in good result.

Catalytic Asymmetric Direct Aldol Reaction of α-Alkyl Azlactones and Aliphatic Aldehydes

An unprecedented highly diastereoselective and enantioselective aldol reaction of α-alkyl azlactones and aliphatic aldehydes was achieved with cinchona alkaloid catalysts. To our knowledge, this reaction provides the first useful catalytic asymmetric access toward β-hydroxy-α-amino acids bearing alkyl substituents, which are structural motifs embedded in many natural products.

The stereoselective synthesis of α-amino aldols starting from terminal alkynes

A new sequential procedure for the stereoselective synthesis of syn α-amino β-oxy ketones starting from terminal alkynes has been developed.

Natural products as platforms for the design of sphingolipid-related anticancer agents

Modulation of sphingolipid metabolism is a promising strategy for cancer therapy that has already opened innovative approaches for the development of pharmacological tools and rationally designed new drugs. On the other hand, natural products represent a classical and well-established source of chemical diversity that has guided medicinal chemists on the development of new chemical entities with potential therapeutic use. Based on these premises, the aim of this chapter is to provide the reader with a general overview of some of the most representative families of sphingolipid-related natural products that have been described in the recent literature as lead compounds for the design of new modulators of sphingolipid metabolism. Special emphasis is placed on the structural aspects of natural sphingoids and synthetic analogs that have found application as anticancer agents. In addition, their cellular targets and/or their mode of action are also considered.

Direct amination of α-substituted nitroacetates using di-tert-butyl azodicarboxylate catalyzed by Hatakeyama's catalyst β-ICD

We report the first example of catalytic asymmetric direct amination of α-monosubstituted nitroacetates using di-tert-butyl azodicarboxylate. The simple and easily available Hatakeyama's catalyst β-ICD 11 was found to be a highly enantioselective catalyst for this reaction.