Since oxazoles have found widespread applications not only as synthetic intermediates
but also as biologically active compounds, much effort has been focused on developing
novel and efficient methods for the synthesis of this heterocycle. From the viewpoint
of green and sustainable chemistry, hypervalent iodine and other halogen reagents
have gained increasing popularity in metal-free oxidative transformation due to their low
toxicity, transition-metal-like reactivity, high stability, easy handling and other benefits. In
this account, our two approaches to the metal-free synthesis of oxazoles by means of a peculiar
activation of alkynes by iodine species are described with the related contexts. One
is iodine(III)-mediated/catalyzed oxidative cycloisomerization reactions of N-propargyl
amides for the preparation of oxazoles bearing various functional groups at their side
chains. In these reactions, iodine(III) species works as a donor of various heteroatomic functional groups as
well as an activator of carbon-carbon triple bonds in a single step. Furthermore, this methodology can be extended
to iodine(III)-mediated/catalyzed oxidative annulation of alkynes and nitriles as another approach, in
which heteroatoms on iodine(III) species are incorporated in the azole rings.
Metal-free transfer hydrochlorination of internal C-C triple bonds with a bicyclo[3.1.0]hexane-based surrogate releasing two molecules of hydrogen chloride
