N-Heterocyclic carbene-catalyzed
formal [3+2] annulation of alkynyl aldehydes and nitrosobenzenes has
been reported. This transformation provided the novel C–X bond
formation under mild conditions in moderate to satisfactory yields.
The catalytic protocol allows for a rapid construction of 2,5-disubstituted
isoxazol-3(2H)-ones and 2,3-disubstituted isoxazol-5(2H)-ones from
the same materials via a highly regioselectively umpolung stratgy.
A concise asymmetric total synthesis of a fusarentin ether (1) with sequential biomimetic transformation to its analogues fusarentin 6,7-dimethyl ether (2), 7-O-demethylmonocerin (3), and (+)-monocerin (4) has been accomplished. The cis-fused furobenzopyranones of 7-O-demethylmonocerin (3) and (+)-monocerin (4) were efficiently constructed via an intramolecular nucleophilic trapping of a quinonemethide intermediate, which was obtained by benzylic oxidation of fusarentin 6-methyl ether (1) using hypervalent iodine reagent.
A new iron(III)‐catalyzed synthesis of β‐oxo sulfones is described that employs vinylarenes and readily available dimethyl sulfoxide (DMSO) with hydrazine and oxygen as the oxidant. The reaction tolerates various functional group substituents on the vinylarene substrates to afford β‐oxo sulfones in moderate to good yields. The cleavage and formation of the C–S bond are the key steps of this transformation.
The first enantioselective total synthesis of the structurally unique nortriterpenoid (-)-walsucochin B has been accomplished through the cationic polyolefin cyclization initiated by chiral epoxide. The core framework and the stereocenters in the natural product were all constructed in this step. A site-selective, late-stage free-radical halogenation and Seyferth-Gilbert homologation was adopted to install the acetylene moiety to synthesize the phenylacetylene. The absolute configuration of walsucochin B was confirmed through enantioselective total synthesis.
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