Tiara[5]arenes (T[5]s), a new class of five‐fold symmetric oligophenolic macrocycles that are not accessible from the addition of formaldehyde to phenol, were synthesized for the first time. These pillar[5]arene‐derived structures display both unique conformational freedom, differing from that of pillararenes, with a rich blend of solid‐state conformations and excellent host–guest interactions in solution. Finally we show how this novel macrocyclic scaffold can be functionalized in a variety of ways and used as functional crystalline materials to distinguish uniquely between benzene and cyclohexane.
The development of
an efficient synthetic route toward rim-differentiated C5-symmetric pillar[5]arenes (P[5]s), whose two
rims are decorated with different chemical functionalities, opens
up successive transformations of this macrocyclic scaffold. This paper
describes a gram-scale synthesis of a C5-symmetric penta-hydroxy P[5] precursor, and a range of highly efficient
reactions that allow functionalizing either rim at will via, e.g.,
sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or
Suzuki–Miyaura coupling. Afterward, BBr3 demethylation
activates another rim for similar functionalizations.
A general and efficient lactonization method of readily available 2-alkynylbenzoates affording biologically important isochromenones has been realized via a solely BF 3 •Et 2 O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF 3 • Et 2 O activates the carbonyl of the ester moiety, rather than the alkyne triple bond, was postulated on the basis of control experiment results. Gram-scale reaction and further application for the assembly of more complex molecules demonstrated the practicability of the protocol.
A class
of novel spirooxindole compounds (2) were
readily synthesized, in a metal-free environment, from N-arylamide derivatives (1) via intramolecular oxidative
cyclization. Direct oxidative C(sp2)–C(sp3) bond formation was realized with the least-studied PhI(OMe)2 as an oxidant, formed in situ from the reaction between PhIO
and MeOH.
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