Use of Elemental Sulfur or Selenium in a Novel One-Pot Copper-Catalyzed Tandem Cyclization of Functionalized Ynamides Leading to Benzosultams

A novel and efficient [Cu]-catalyzed
one-pot regio- and stereospecific synthesis of benzo­[1,4,2]­dithiazine
1,1-dioxides and benzo­[1,4,2]­thiaselenazine 1,1-dioxides by cyclization
of functionalized ynamides with elemental sulfur/selenium has been
developed. Its generality is elegantly illustrated by extension to
benzo­dithiazepines and benzo­thia­selenazepines. Involvement
of water in the reaction is demonstrated by the incorporation of 2D at the olefinic site by using D2O in place of
water. Selective oxidation at sulfur in benzo­[1,4,2]­dithiazine 1,1-dioxide
by using mCPBA as the oxidizing agent is also described.