N‑Heterocyclic Carbene-Catalyzed Formal [3+2] Annulation of Alkynyl Aldehydes with Nitrosobenzenes: A Highly Regioselective Umpolung Strategy

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.