A new protocol for the cyclization of N-alkenylamides using chloramine-T and iodine is described. When N-alkenylsulfonamides are treated with chloramine-T and iodine, three- to six-membered N-heterocycles are obtained with complete stereoselectivity. The method is compatible with the cyclization of the allylbenzamide or allylbenzthioamide to afford an oxazoline or thiazoline derivative, respectively. Mechanistic studies indicate that the chloramine-T/I-2 system functions as an effective iodonium species. (c) 2006 Elsevier Ltd. All rights reserved.
Practical and Convenient Synthesis of <i>N</i>-Heterocycles: Stereoselective Cyclization of <i>N</i>-Alkenylamides with <i>t</i>-BuOI under Neutral Conditions
[Structure: see text] tert-Butylhypoiodite (t-BuOI) was found to be a powerful reagent for the cyclization of N-alkenylamides leading to a variety of N-heterocycles under extremely mild conditions. When N-alkenylsulfonamides were employed in the reaction, three- to six-membered saturated N-heterocycles were obtained in good to excellent yields with complete stereoselectivity. The method was applicable