Dynamic behaviour of monohaptoallylpalladium species: internal coordination as a driving force in allylic alkylation chemistry

Xie, Lan‐Gui; Bagutski, Viktor; Wolf, Lawrence M.; Schmidts, Volker; Hofmann, Kathrin; Wirtz, Cornelia; Thiel, Walter; Thiele, Christina M.; Maulide, Nuno

doi:10.1039/c5sc01867f

Cited by 8 publications

(16 citation statements)

References 51 publications

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“…Intrigued by the mechanistic complexity of this system, we have sought structural characterization of intermediates . One such venture is depicted in Scheme , where equimolar amounts of chlorocarboxylic acid cis - 41 , a Pd(0) source and chiral ligand L3a were admixed.…”

Section: Enantioselective Synthesis Of Cyclobutenesmentioning

confidence: 99%

Cyclobutenes: At a Crossroad between Diastereoselective Syntheses of Dienes and Unique Palladium-Catalyzed Asymmetric Allylic Substitutions

2016

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The rich chemistry of cyclobutanes is underpinned by a large body of synthetic literature devoted to their synthesis and decoration. This is motivated by the widespread representation of cyclobutane moieties in biologically active natural products and man-made molecules. Surprisingly, this vast array of knowledge finds no parallel in the chemistry of cyclobutenes, their unsaturated analogues. In particular, a dearth of methods to synthesize enantioenriched cyclobutenes is apparent upon cursory investigation of the literature. As a leading example, the photocycloaddition of maleic anhydride to acetylene or dichloroethylene, probably a benchmark of cyclobutene synthesis, delivers a meso cyclic anhydride which can be further converted to a cyclobutene product by enantioselective desymmetrization by ring opening. Nonetheless, such an approach delivers products with a rather inflexible substitution pattern around the four-membered ring. The lack of general approaches has motivated our group and others to develop novel routes to cyclobutene scaffolds, leading to the development of a strategy that combines photochemistry and catalysis. Indeed, we have coupled the simple and efficient photochemical isomerization of 2-pyrone into a strained bicyclo[2.2.0] lactone with palladium-catalyzed allylic alkylation as a simple and versatile access to functionalized cyclobutenes. Several nucleophiles can be added to the activated, strained intermediate, including malonate anions and azlactones. The products are mono- and bicyclic building blocks richly decorated with functional groups. Importantly, they are formed with high levels of diastereoselectivity as expected by the tenets of palladium-catalyzed allylic alkylation, which posit that the oxidative addition and nucleophilic capture steps proceed with inversion of configuration, resulting in overall retention (inversion + inversion). However, the transposition of the methodology to an asymmetric version subsequently led to the surprising discovery of a family of highly enantioselective, diastereodivergent catalytic processes. Indeed, we observed a ligand-dependent stereochemical outcome for a range of palladium-catalyzed allylic alkylations affording either overall retention or overall inversion of configuration, and that with very high levels of enantio- and diastereoselectivity. The new family of diastereodivergent reactions enables the conversion of the aforementioned racemic bicyclo[2.2.0] lactone into each of 4 stereoisomeric products, at will. Although the mechanistic details at the origin of this unusual stereodivergence are not yet fully elucidated, it became clear through our studies that unique Pd-allyl complexes, residing preferentially as their σ-(monohapto)-bound isomers, are at the heart of the process. The cyclobutenes prepared can also engage in electrocyclic ring-opening reactions (often spontaneous depending on the substitution pattern) that link this chemistry with that of diene and polyene frameworks. Using the strategies laid out above, our group was then ab...

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Section: Enantioselective Synthesis Of Cyclobutenesmentioning

confidence: 99%

Cyclobutenes: At a Crossroad between Diastereoselective Syntheses of Dienes and Unique Palladium-Catalyzed Asymmetric Allylic Substitutions

2016

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“…Apart from the obvious requirements on solubility, the small molecule may also not tolerate the presence of the alignment medium (or vice versa) and decompose (or lead to destabilization or decomposition of the medium). However, after rigorous trials, compatible media were found for moderately unstable compounds like Pd complexes involved in homogeneous catalysis [57,58] and even very reactive organolithium species. [59][60][61] For LLCs, sample preparation generally involves preparation of the alignment medium first, i.e.…”

Section: Alignment Mediamentioning

confidence: 99%

Perspectives in the application of residual dipolar couplings in the structure elucidation of weakly aligned small molecules

Schmidts

2016

Magnetic Reson in Chemistry

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This perspective article aims to review the general methodology in the application of residual dipolar couplings (RDCs) in the structure elucidation of small molecules and give the author's view on challenges for future applications. Recent improvements in the availability of alignment media, new pulse sequences for the measurement of couplings and improvements in the analysis software have garnered widespread interest in the technique. However, further generalization is needed in order to make RDC analysis into a truly "routine" method.

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“…In this regard, the Maulide group pioneered the investigations of the reactivity of strained cyclic π-allylpalladium complexes by using 2-oxabicyclo[2.2.0]hex-5-en-3-one and 4-chlorocyclobut-2-ene carboxylic acid as substrates, achieving the diastereoselective and enantioselective synthesis of functionalized cyclobutenes (Scheme b) . In 2013, the same group further studied the structure and reactivity of cyclobuten-3-yl palladium complexes in detail and discovered that the strained cyclic π-allylpalladium intermediates were inclined to undergo electrocyclic ring opening to deliver dienyl palladium species . Despite the remarkable progress, the laborious access and instability of the allylic precursors restrict the comprehensive investigation of strained cyclic π-allylpalladium complexes.…”

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confidence: 99%

Cross-Coupling of Cyclobutenone N-Tosylhydrazones with Organohalides: Access to Conjugated Enynes and Enallenes via a Strained Allylpalladium Intermediate

Ning

Chen

et al. 2022

Org. Lett.

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A palladium-catalyzed cross-coupling reaction of cyclobutenone N-tosylhadrazones with organohalides is disclosed. The protocol involves the generation of a strained allylpalladium intermediate from readily available starting materials through palladium carbene migratory insertion, which undergoes electrocyclic ring opening and β-hydride elimination for the production of conjugated enynes and enallenes. The broad substrate scope, good to excellent yields, and tunable product diversity make the protocol potentially useful in organic synthesis.

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Dynamic behaviour of monohaptoallylpalladium species: internal coordination as a driving force in allylic alkylation chemistry

Abstract: Structural and reactivity studies of internally coordinated monohaptoallylpalladium(ii) complexes.

Cited by 8 publications

References 51 publications

Cyclobutenes: At a Crossroad between Diastereoselective Syntheses of Dienes and Unique Palladium-Catalyzed Asymmetric Allylic Substitutions

Cyclobutenes: At a Crossroad between Diastereoselective Syntheses of Dienes and Unique Palladium-Catalyzed Asymmetric Allylic Substitutions

Perspectives in the application of residual dipolar couplings in the structure elucidation of weakly aligned small molecules

Cross-Coupling of Cyclobutenone N-Tosylhydrazones with Organohalides: Access to Conjugated Enynes and Enallenes via a Strained Allylpalladium Intermediate

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