Reagent-Controlled Divergent Synthesis of 2‑Amino-1,3-Benzoxazines and 2‑Amino-1,3-Benzothiazines

A reagent-controlled chemoselective process has been
devised for
the synthesis of 4H-1,3-benzoxazines and related
biologically important heterocycles in high yields under mild conditions.
These scaffolds could be efficiently constructed using two different
chemoselective reactions that rely on the choice of reagents and reaction
conditions. The treatment of various 2-amino-arylalkyl alcohols with
isothiocyanates afforded thiourea intermediates, which were reacted in situ with molecular iodine in the presence of triethylamine
to give 2-amino-4H-1,3-benzoxazines, whereas the
corresponding 2-amino-4H-1,3-benzothiazines were
obtained by the reaction of thiourea intermediates in the presence
of T3P (a mild cyclodehydrating agent) and triethylamine as the base.
The described protocol represents the first example for the synthesis
of 4H-1,3-benzoxazines via the dehydrosulfurization
method using molecular iodine as the reagent.