RESUMEN
The activation of ethers by weak interactions is a long-standing objective in supramolecular catalysis, but yet it remains an underdeveloped topic. The obstacles towards solving this problem are prominent since it is difficult for a weak interaction to cleave a relatively strong C-O σ-bond and moreover, the ionic intermediate composing of an alkoxide ion and an electrophilic carbocation would deactivate weak interaction donors. Herein, we describe a distinctive activation mode, dual Se···π and Se···O bonding, that could activate benzylic as well as allylic ether C-O σ-bonds to achieve cyclization, coupling and elimination reactions. This dual Se···π and Se···O bonding catalysis approach could tolerate various alkoxide leaving groups, while the other representative weak interaction donors showed no catalytic activity.
RESUMEN
The activation of the triple bond of alkynes was dominated by transition metals, while it is difficult for organocatalysts to play an effective role in this realm. Herein, we describe the activation of alkynes by chalcogen bonding, and the weak Seâ¯π interaction was capable of catalyzing the intramolecular cyclization of 1,6-diynes, thus adding a new capability in the list of supramolecular catalysis.
RESUMEN
A formal [3 + 2] cycloaddition between ynamides and unprotected isoxazol-5-amines has been developed in the presence of catalytic AgNTf2 in an open flask. By the protocol, a variety of functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives can be obtained in up to 99% yield. The reaction mechanism might involve the generation of an unusual α-imino silver carbene intermediate (or a silver-stabilized carbocation) and subsequent cyclization/isomerization to build the significant pyrrole-3-carboxamide motif. The reaction features the use of an inexpensive catalyst, simple reaction conditions, simple work-up without column chromatographic purification for most of products and high yields.