3 research outputs found

    Gold-Catalyzed Unexpected Ring Transformation of Pyrimidodiazepine Derivatives

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    Pyrimidodiazepine derivatives underwent an unexpected gold-catalyzed retro-Mannich-type carbon–carbon bond cleavage and intramolecular nucleophilic cyclization. The pyrimidodiazepines bearing an alkyne moiety showed novel orthogonal reactivity in the presence of a gold catalyst, as opposed to the alkynophilicity that is commonly observed with gold catalysts. The ring transformation reaction of pyrimidodiazepines probably proceeds through an acyclic iminium intermediate. The potential of this synthetic method for the skeletal diversification of pyrimidine-containing macrocycles was also demonstrated

    Synthesis and Library Construction of Privileged Tetra-Substituted Δ<sup>5</sup>‑2-Oxopiperazine as β‑Turn Structure Mimetics

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    In this study, we developed an efficient and practical procedure for the synthesis of tetra-substituted Δ<sup>5</sup>-2-oxopiperazine that mimics the bioactive β-turn structural motif of proteins. This synthetic route is robust and modular enough to accommodate four different substituents to obtain a high level of molecular diversity without any deterioration in stereochemical enrichment of the natural and unnatural amino acids. Through the <i>in silico</i> studies, including a distance calculation of side chains and a conformational overlapping of our model compound with a native β-turn structure, we successfully demonstrated the conformational similarity of tetra-substituted Δ<sup>5</sup>-2-oxopiperazine to the β-turn motif. For the library construction in a high-throughput manner, the fluorous tag technology was adopted with the use of a solution-phase parallel synthesis platform. A 140-membered pilot library of tetra-substituted Δ<sup>5</sup>-2-oxopiperazines was achieved with an average purity of 90% without further purification

    Gold-Catalyzed Intermolecular Reactions of Propiolic Acids with Alkenes: [4 + 2] Annulation and Enyne Cross Metathesis

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    A gold-catalyzed intermolecular reaction of propiolic acids with alkenes led to a [4 + 2] annulation or enyne cross metathesis. The [4 + 2] annulation proceeds with net <i>cis-</i>addition with respect to alkenes and provides an expedient route to α,β-unsaturated δ-lactones, for which preliminary asymmetric reactions were also demonstrated. For 1,2-disubstituted alkenes, unprecedented enyne cross metathesis occurred to give 1,3-dienes in a completely stereospecific fashion. DFT calculations and experiments indicated that the cyclobutene derivatives are not viable intermediates and that the steric interactions during concerted σ-bond rearrangements are responsible for the observed unique stereospecificity