Jeffery Richardson

Total Synthesis of Aigialomycin D using a One-Pot Ketene Generation−Trapping−Aromatization Sequence

The total synthesis of aigialomycin D, without the need for phenol protection, was carried out using the C-acylation of a keto-dioxinone dianion, a cascade sequence consisting of ketene generation, alcohol trapping and aromatization, and ring-closing metathesis.

Two-Step Cyanomethylation Protocol: Convenient Access to Functionalized Aryl- and Heteroarylacetonitriles

A two-step protocol has been developed for the introduction of cyanomethylene groups to metalated aromatics through the intermediacy of substituted isoxazoles. A palladium-mediated cross-coupling reaction was used to introduce the isoxazole unit, followed by release of the cyanomethylene function under thermal or microwave-assisted conditions. The intermediate isoxazoles were shown to be amenable to further functionalization prior to deprotection of the sensitive cyanomethylene motif, allowing access to a wide range of aryl- and heteroaryl-substituted acetonitrile building blocks.

Total synthesis of citrafungin A.

The antifungal natural product citrafungin A was synthesized using, as key steps, an asymmetric aldol reaction of a chiral oxazolidinone, diastereoselective alkylation of a chiral 1,3-dioxolan-2-one, semihydrogenation of an enyne, and selective methyl ester deprotection.

A Method for Identifying and Developing Functional Group Tolerant Catalytic Reactions: Application to the Buchwald–Hartwig Amination

Transition-metal catalysis has revolutionized organic synthesis, but difficulties can often be encountered when applied to highly functionalized molecules, such as pharmaceuticals and their precursors. This results in discovery collections that are enriched in substances possessing less desirable properties (high lipophilicity, low polar surface area). Masking groups are often employed to circumvent this problem, which is in opposition to the inherent ideality of these methods for green chemistry and atom economy. A general screening methodology, related to robustness screening described by Glorius et al., builds a broad understanding of the impact of individual functional groups on the success of a transformation under various conditions and provides a simple framework for identifying new conditions that tolerate challenging functional groups. Application of this approach to profile the conditions for the Buchwald-Hartwig amination and rapidly identify bespoke conditions for challenging substrate classes is described.

Kinetic Resolution of 2-Substituted Indolines by N-Sulfonylation using an Atropisomeric 4-DMAP-N-oxide Organocatalyst

The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6-19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.

Improved Substrate Scope in the Potassium Hexacyanoferrate(II)-Based Cyanation for the Synthesis of Benzonitriles and Their Heterocyclic Analogues

The use of Pd(DPEPhos)Cl2 (P26) as a catalyst for the formation of benzonitriles and their heterocyclic analogues provides excellent complementarity to existing catalysts, allowing highly electron-deficient heterocyclic aryl halides to be efficiently converted to the corresponding nitriles using K4[Fe(CN)6]) as cyanide source. This catalyst significantly enhances the scope of this reaction to include a number of substrates that are highly relevant for pharmaceutical and agrochemical applications. Importantly, not only does this cyanation method employ a nontoxic cyanide source, simple semiquantitative testing suggests that, unlike many other methods, no free cyanide is present in the reaction mixture or during a variety of potential workups, thus improving the safety aspects of this method from initial setup through to product isolation. Finally, developing and testing a series of convenient cyanation kits has allowed facile application and broader adoption of this method in our laboratories.

Short, Gram-Scale Syntheses of β- and γ-Lycorane Using Two Distinct Photochemical Approaches

The synthesis of two diastereomeric members of the lycorane alkaloid family is reported. Although the routes are quite different in their approach, both involve the use of photochemistry as a key step, enabling the synthesis of gram quantities in the case of β-lycorane.