Development of Synthetic Organic Reaction through the Formation of Halocyclization Intermediate as an Activating Method

We report here the results of synthetic organic reactions which proceed under mild conditions through the formation of cationic halocyclization intermediates. In the presence of I₂ and collidine or lutidine, α-iodination reactions of unsaturated carboxamides and N-allylic carboxamides proceed in good yields through the activation of α-hydrogens by the formation of cyclic iminium ethers (iodolactonization intermediates). The iodine-mediated method can be also applied to the activation of enamide derivatives; that is, in the presence of I₂, the Diels-Alder reactions of N-allylic enamides which are unreactive dienophiles, proceed in good yield through the formation of the cyclic iminium ether. These activation processes are successfully extended to asymmetric α-iodination of unsaturated carboxamides having homochiral 2,5-disubstituted pyrrolidine and asymmetric Diels-Alder reaction using novel axially chiral N-acryl anilide. Furthermore, the reactions of p-methoxybenzyl pentenyl ether with NIS and O-pentenyl oxime with NBS resulted in the activation of C-O bond and N-O bond through the formation of cationic haloetherification intermediates, and the following reaction with alchols and migration of anti-substituent gave p-methoxybenzylation and Beckmann rearrangement products in good yields, respectively.