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 procee d under mild conditions through the formation of cationic halocyclizat ion intermediates. in the presence of I-2 and collidine or lutidine, a lpha-iodination reactions of unsaturated carboxamides and N-aIlylic ca rboxamides proceed in good yields through the activation of a-hydrogen s by the formation bf cyclic iminium ethers (iodolactonization interme diates). The iodine-mediated method can be also applied to the activat ion of enamide derivatives;that is, in the presence of I-2, the Diels- Alder reactions of N-allylic enamides which are unreactive dienophiles , proceed in good yield through the formation of the cyclic iminium et her. These activation processes are successfully extended to asymmetri c a-iodination of unsaturated carboxamides having homochiral 2,5-disub stituted pyrrolidine and asymmetric Diels-Alder reaction using novel a xially chiral N-acryl anilide. Furthermore, the reactions of p-methoxy benzyl 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 ca tionic haloetherification intermediates, and the following reaction wi th alchols and migration of anti-substituent gave p-methoxybenzylation and Beckmann rearrangement products in good yields, respectively.