Bartosz Bisek

Tight chelation of enolate by lithium alters the selectivity of tandem palladium-catalyzed cyclization/coupling of terminal alpha-homopropargyl-beta-ketoesters with aryl halides. In the presence of LiOH, substituted cyclopentenes are preferentially formed via 5-endo-dig carbocyclization, in contrast to the 6-exo-dig oxocyclization exclusively observed in the absence of a hard, chelating metal center. The disclosed transformation, featuring mild conditions and broad functional group tolerance, can be applied for a variety of (hetero)aryl bromides as well as aryl and vinyl triflates.

An unprecedented DDQ-mediated oxidative aromatization of 2-bezylidene-dihydrofurans yielding 2-alkenyl-furans is disclosed. Integration of this transformation with a prior Pd-catalyzed reaction of α-propargylic-β-ketoesters and (hetero)aryl halides into a one-pot cascade process opens a direct modular route to highly substituted 2-vinyl-furans. Experimental and computational studies reveal that the crucial step of the oxidative-aromatization involves facile hydride transfer from the dihydrofuran ring to the O-center of DDQ.

Pd‐catalyzed tandem cyclization/coupling of internal β‐propargylic‐β‐ketoesters with (hetero)aryl bromides is described. Two protocols are established which selectively lead to 2‐benzylidene‐dihydrofurans, when isomerization is inhibited under mild conditions (temp. ≤40 °C and weak base – K₂CO₃), or to 2‐benzyl‐furans when base‐induced aromatization is enabled. A catalytic cycle involving oxidative addition, substitution of bromide with alkyne, rate limiting anti‐selective 5‐exo‐dig oxocyclization followed by fast deprotonation of the oxonium intermediate, and reductive elimination is proposed based on detailed experimental and theoretical studies. magnified image

Article published online: 13 June 2022 Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Epoxydiazocines belong to the rare class of small V-shaped molecules, closely related to Tröger’s base. Due to their intriguing, unique structure, they could serve as molecular building blocks for supramolecular chemistry. An extensive review on their synthesis is contained in this article. Moreover, our recent findings devoted to efficient and easily scalable synthesis of fluorinated epoxy[1,5][b,f]diazocines through solvent-free base-catalyzed condensation of ortho-aminophenones is provided. The unique V-shaped structure was confirmed by X-ray crystal structure analysis. Furthermore, the rigidity of the epoxy­diazocine skeleton allowed for racemate separation and the configuration of enantiomers was established by combining quantum chemical calculations and chiroptical methods.1 Introduction2 Synthetic Efforts Towards Epoxydibenzo[b,f][1,5]diazocines3 Synthetic Efforts Towards Fluorinated Epoxydibenzo[b,f][1,5]diazocines4 Conclusion