David W. Lupton’s research while affiliated with Monash University (Australia) and other places

Herein, we report a (3 + 2) cycloaddition to deliver an array of cyclopentenes. Typically, the reaction involves electron-poor terminal alkynes and ketomalonate partners, however numerous structural modifications to the coupling partners have been accommodated to enable 45 examples of the reaction to be completed. Mechanistic studies highlight the role of alkyne slow addition to avoid undesired alkyne deprotonation. Application to the synthesis of pre-methylenomycin C lactone, an inter-mediate in methylenomycin biosynthesis with potent activity against Gram-positive bacteria, demonstrates the robust nature and good scalability of the reaction.

Herein we report a catalytic enantioselective (3+2) annulation, in which a vinyl phosphonium intermediate serves as the 2‐carbon component. The reaction involves an α‐umpolung β‐umpolung coupling sequence, enabled by β‐haloacrylates and chiral enantioenriched phosphepine catalysts. The reaction shows good generality, providing access to an array of cyclopentenes, with mechanistic studies supporting stereospecific formation of the vinyl phosphonium intermediate which, then undergoes annulation with turn over limiting catalyst elimination. Beyond defining a new approach to cyclopentenes, these studies demonstrate that β‐haloacrylates can replace ynoates in reaction designs that require exclusive umpolung coupling at the α‐ and β‐positions.

Herein we report a catalytic enantioselective (2 + 3) cycloaddition in which a vinyl phosphonium intermediate serves as the 2-carbon component. The reaction involves an umpolung umpolung coupling sequence enabled by haloacrylates and chiral enantioenriched phosphepine catalysts. The reaction shows good generality providing access to an array of cyclopentenes, with mechanistic studies supporting stereospecific formation of the vinyl phosphonium intermediate which then undergoes annulation with turn over limiting catalyst elimination. Beyond defining a new approach to cyclopentenes these studies demonstrate that haloacrylates can replace ynoates in reaction designs that require exclusive umpolung coupling at both carbons

Herein we report a catalytic enantioselective (3+2) annulation, in which a vinyl phosphonium intermediate serves as the 2‐carbon component. The reaction involves an α‐umpolung β‐umpolung coupling sequence, enabled by β‐haloacrylates and chiral enantioenriched phosphepine catalysts. The reaction shows good generality, providing access to an array of cyclopentenes, with mechanistic studies supporting stereospecific formation of the vinyl phosphonium intermediate which, then undergoes annulation with turn over limiting catalyst elimination. Beyond defining a new approach to cyclopentenes, these studies demonstrate that β‐haloacrylates can replace ynoates in reaction designs that require exclusive umpolung coupling at the α‐ and β‐positions.

Lanthanide ions have ideal chemical properties for catalysis, such as hard Lewis acidity, fast ligand-exchange kinetics, high coordination-number preferences and low geometric requirements for coordination. As a result, many small-molecule lanthanide catalysts have been described in the literature. Yet, despite the ability of enzymes to catalyse highly stereoselective reactions under gentle conditions, very few lanthanoenzymes have been investigated. In this work, the mononuclear binding of europium(III) and gadolinium(III) to the active site of a mutant of the model enzyme phosphotriesterase are described using X-ray crystallography at 1.78 and 1.61 Å resolution, respectively. It is also shown that despite coordinating a single non-natural metal cation, the PTE-R18 mutant is still able to maintain esterase activity.

Dual nucleophilic phosphine photoredox catalysis is yet to be developed due to facile oxidation of the phosphine organocatalyst to the phosphoranyl radical cation. Herein, we report a reaction design that avoids this event and exploits traditional nucleophilic phosphine organocatalysis with photoredox catalysis to allow the Giese coupling with ynoates. The approach has good generality, while its mechanism is supported by cyclic voltametric, Stern–Volmer quenching, and interception studies.

Dual nucleophilic phosphine photoredox catalysis is yet to be developed due to facile oxidation of the phosphine organocatalyst to the phosphoranyl radical cation. Herein, we report a reaction design that avoids this event and exploits traditional nucleophilic phosphine organocatalysis with photoredox catalysis to allow the Giese coupling with ynoates. The approach has good generality, while its mechanism is supported by cyclic voltametric, Stern–Volmer quenching, and interception studies.

ConspectusConjugate acceptors are one of the most common electrophilic functional groups in organic synthesis. While useful in a diverse range of transformations, their applications are largely dominated by the reactions from which their name is derived (i.e., as an acceptor of nucleophiles in the conjugate position). In 2014, we commenced studies focused on their ability to undergo polarity inversion through the conjugate addition of Lewis base catalysts. The first step in this process provides an enolate, from which the well-developed Rauhut-Currier (RC) and Morita-Baylis-Hillman (MBH) reactions can occur; however, tautomerization to provide a species in which the β-carbon of the conjugate acceptor can now act as a donor is also possible. When we commenced studies on this topic, reaction designs with this type of species, particularly when accessed using N-heterocyclic carbenes (NHCs), had been reported on only a handful of occasions. Despite a lack of development, conceptually it was felt that reactions taking advantage of polarity switching by Lewis base conjugate addition have a number of desirable features. Perhaps the most significant is the potential to reimagine a ubiquitous functional group as an entirely new synthon, namely, a donor to electrophiles from the conjugate position.Our work has focused on catalysis with both simple conjugate acceptors and also those embedded within more complicated substrates; the latter has allowed a series of cycloisomerizations and annulation reactions to be achieved. In most cases, the reactions have been possible using enantioenriched chiral NHCs or organophosphines as the Lewis base catalysts thereby delivering enantioselective approaches to novel cyclic molecules. While related chemistry can be accessed with either family of catalyst, in all cases reactions have been designed to take advantage of one or the other. In addition, a fine balance exists between reactions that exploit the initially formed enolate and those that involve the polarity-inverted β-anion. In our studies, this balance is addressed through substrate design, although catalyst control may also be possible. We consider the chemistry discussed in this Account to be in its infancy. Significant challenges remain to be addressed before our broad aim of discovering a universal approach to the polarity inversion of all conjugate acceptors can be achieved. These challenges broadly relate to chemoselectivity with substrates bearing multiple electrophilic functionalities, reliance upon the use of conjugate acceptors, and catalyst efficiency. To address these challenges, advances in catalyst design and catalyst cooperativity are likely required.