We herein report the use of ethyl but-3-ynoate as a C2 building block for asymmetric (4+2)-heterocycloadditions with various Michael acceptors. Upon using chiral isochalcogenoureas as Lewis base catalysts, these reactions can be carried out with good to excellent control of the regioselectivity, diastereoselectivity, and enantioselectivity.

Cross-coupling and nucleophilic aromatic substitution reactions of 2,4-dihalopyrimidines generally favor reaction at the C4 site, especially in the absence of other substituents on the pyrimidine ring. Here we review our recent discovery of reaction conditions that enable C2-selective Pd-catalyzed C-S coupling of unsubstituted 2,4-dichloropyrimidines, as well as some substituted derivatives. The unusual C2-selectivity complements previously established cross-coupling methods and raises interesting mechanistic questions about oxidative addition in cross-coupling catalytic cycles.

Activity-based protein profiling (ABPP) technology has served as a powerful platform for studying proteins for more than two decades. However, the further growth of this field depends on the development of new probe structures to expand the proportion of the proteome that can be studied using these methods. Inspired by previous reports of succinimide-containing covalent inhibitors for proteases, we synthesized a panel of potential probe structures with a succinimide reactive group and a terminal alkyne tag suitable for subsequent azide-alkyne click chemistry. Members of this panel with an -arylsulfonyl linker produce labeling of both purified serine proteases as well as proteins in complex cellular lysates. We found that one of these probes labels the human rhomboid protease RHBDL2 at low micromolar concentrations and can be competed with active-site inhibitors. Our studies establish succinimide as a new reactive group for the development of activity-based probes and offer a new chemical tool for studying a class of enzymes with limited functional characterization.

This account highlights an iron-catalyzed exclusively 1,2--selective glycosylation method for aminoglycoside synthesis. This selective nitrogen atom transfer reaction is effective for a broad range of glycosyl donors and acceptors, and it can be operated in a reiterative fashion and scaled up to the multi-gram scale. Mechanistic studies revealed a unique yet generally applicable glycosylation mechanism in which the iron catalyst activates a glycosyl acceptor and an oxidant when it facilitates the cooperative atom transfer of both moieties to a glycosyl donor in an exclusively -selective manner.

Verruculogens are fumitremorgin alkaloids that contain an eight-membered endoperoxide ring. Due to their unusual structure and bioactivity, there has been much interest in these natural products since their discovery over forty years ago. Similarly, interest in their biosynthesis resulted in the discovery of verruculogen synthase (FtmOx1) that catalyzes endoperoxide formation in these natural products. Herein, we describe our work in this area through the chemoenzymatic synthesis of 13-oxoverruculogen by endoperoxidation of a substrate analog using FtmOx1.

Metal-catalyzed cross-coupling reactions have transformed molecular synthesis. Although metal-catalyzed reactions have been used for cross-electrophile coupling reactions, they remain challenging due to homodimer formation. Recently, our group developed an iron-catalyzed cross-electrophile coupling of benzyl halides and disulfides to produce thioethers without the use of an exogenous reductant or photoredox conditions, and with undetectable levels of elimination. This Synpacts article highlights both our design strategy to obviate detrimental homodimer formation and the generality of the method.

We present our synthetic endeavors towards the meroterpenoid ganoapplanin. This natural product was isolated from a fungus in 2016 and was found to be an inhibitor for T-type voltage-gated calcium channels. Our synthetic approach is based on a powerful intramolecular Giese cyclization/intermolecular aldol cascade to link the northern aromatic to the southern terpenoid fragment. This article highlights the synthetic studies that ultimately led to the successful development of the key cascade reaction, culminating in the first total synthesis of ganoapplanin. 1Introduction2Synthesis of the Southern Terpenoid Fragment3Synthesis of the Northern Terpenoid Fragment4Triethylborane Mediated Giese Cyclization/Aldol Reaction Cascades5Completion of the Total Synthesis of Ganoapplanin6Conclusion.

Acetal substitution reactions can proceed by a number of mechanisms, but oxocarbenium ion intermediates are involved in many of these reactions. Our research has focused on understanding the conformational preferences, structures, and reactions of these intermediates. This Account summarizes our observations that electrostatic effects play a significant role in defining the preferred conformations, and that torsional effects determine how those intermediates react. Neighboring-group effects are not as straightforward as they might seem, considering that oxocarbenium ion intermediates are in equilibrium with structures that involve stabilization by a nearby substituent.

Retrosynthetic simplicity is introduced as a metric by which methods can be evaluated. An argument in favor of reactions which are retrosynthetically simple is put forward, and recent examples in the context of skeletal editing from my own laboratory as well as contributions from others are analyzed critically through this lens.

The synthetic potential of unsymmetrically substituted aryne intermediates is significantly hindered by regioselectivity issues. Current methods for inducing regioselectivity all rely on substrate control and are focused on non-metallated arynes. Before our initial disclosure, there was no systematic study regarding the regioselectivity of metal-catalyzed aryne reactions. By exploiting ligand control, we have induced regioselectivity in a palladium-catalyzed aryne annulation to form phenanthridinones (up to 9:91 r.r.). Through this study we have investigated: ligand effects, influence of steric perturbation, and the impact of the aryne precursor.

Enamine -oxides act as a chemical linchpin bridging two bioorthogonal associative and dissociative reactions. This article describes the design of enamine -oxides; their synthesis through the retro-Cope elimination reaction; the use of solvent, hyperconjugation, strain, and rehybridization effects to achieve bioorthogonal reactivity; and their rapid reductive cleavage with diboron reagents. The coordinated assembly and disassembly of the enamine -oxide motif constitutes a powerful chemical operation that enables the attachment and detachment of small molecules from biomacromolecules in a biological setting.

Potassium trifluoroborates have gained significant utility as coupling partners in organic synthesis, particularly in the Suzuki-Miyaura coupling reaction. Recently, they have also been used as radical precursors under oxidative conditions to generate carbon-centered radicals. These versatile reagents have found new applications in photoredox catalysis, including radical substitution, conjugate addition reactions, and transition metal dual catalysis. In addition, this photomediated redox neutral process has enabled radical-radical coupling with persistent radicals in the absence of a metal, and this process remains to be fully explored. In this study, we report the radical-radical coupling of benzylic potassium trifluoroborate salts with isolated acyl azolium triflates, which are persistent radical precursors. The reaction is catalyzed by an organic photocatalyst and forms isolable tertiary alcohol species. These compounds can be transformed into a range of substituted ketone products by simple treatment with a mild base.

General protocols for the N-functionalization of 1,2-azaborines with C(sp), C(sp), or C(sp) electrophiles are described. The syntheses of a new parental BN isostere of -stilbene and a BN isostere of a lisdexamfetamine derivative were accomplished with the developed methodology.

Rh-catalyzed asymmetric hydroboration of enol carbamates yields α-boryl carbamates in good enantioselectivity. The enol carbamate starting materials can be prepared with moderate selectivity using a modified Juila olefination and used as an mixture, taking advantage of the faster reactivity of the major isomer in the directed hydroboration. Optically active α-boryl carbamates participate in a Matteson-type homologation with Grignard reagents in which the O-carbamate is substituted with high conservation of optical activity to provide enantioenriched secondary boronic esters.

A synthesis of (±)-phyltetralin is reported. Notable features of the synthesis include a diastereoselective Cu/Pd-catalyzed arylboration reaction and a Matteson homologation.

Our group's discovery of lithium-isothiourea-boronate-catalyzed Matteson homologations is chronicled. Chiral thiourea dual-hydrogen bond donors were initially found to promote enantioselective dichloromethyl boronate rearrangements, albeit with poor reproducibility. Systematic investigations of the fate of the thiourea led to the discovery that lithium-isothiourea-boronate derivatives were being generated in situ as highly enantioselective catalytically active species. The optimal lithium-isothiourea-boronate catalyst displays significant generality in the rearrangement of primary alkyl migrating groups, affording synthetically valuable α-chloro boronic ester products with consistently high enantioselectivities. The catalyst is proposed to act as a structurally rigid chiral framework that precisely positions two lithium cations to enable a dual-lithium-mediated chloride abstraction.

Electrochemical potentials of photocatalysts are solvent dependent. One of the largest discrepancies is observed when water is used in place of organic solvents as the reaction media. Unfortunately, the redox potentials for many photocatalysts in water have not been determined, at least under one unifying set of conditions, and this greatly hinders the rational design of sustainable and biocompatible photoredox reactions. Herein, we measure the spectral and electrochemical properties of the most common photoredox catalysts in water and catalog their absorption and fluorescence maxima and ground- and excited-state potentials.

This Account describes new reactions that have been developed in the Johnson laboratories at UNC Chapel Hill enabled by considerations of N-O bond cleavage. Three main case studies are highlighted: the metal-catalyzed electrophilic amination of -acyl hydroxyl amines, multihetero-Cope rearrangements driven by O-N bond breakage, and merged dearomatization/N=O cycloadditions for the synthesis of complex 4-aminocyclohexanols such as those found in the natural product tetrodotoxin.

This Account summarizes efforts in our group toward synthesis of heterocycles in the past decade. Selected examples of transannulative heterocyclizations, intermediate construction of reactive compounds to these important motifs, and newer developments of a radical approach are outlined.

Direct functionalization of alkynes under oxidative conditions is challenging, as alkynes are usually recalcitrant towards typical oxidants. Herein, we communicate a strategy for the divergent functionalization of alkynes with photoexcited acridinium organic dyes, presumably via the formation of vinyl cation radicals as key intermediates. Based on the nature of the nucleophiles, different types of difunctionalized products were obtained in moderate to good yields. Addition of lithium Lewis acids resulted in a surprising reversal of diastereocontrol.

The alkaloids are a family of monoterpene indole alkaloids possessing a characteristic azabicyclononane scaffold, which has been assembled by several synthetic methods. Herein we review those approaches that have adopted a biomimetic approach to unite heterocyclic synthons with chiral pool monoterpenes. Throughout this discussion, the tendency of monoterpenes like α-pinene and limonene to undergo racemization is highlighted, revealing the challenges in developing stereospecific syntheses of these alkaloids. Finally, we provide a brief discussion of how these synthetic efforts have enabled the structural confirmation and elucidation of the alkaloids' absolute configurations, including our own recent efforts to employ bioactivity data to deduce the naturally occurring configuration of the quinoline alkaloid aristoquinoline.