The use of chiral diferrocenyl diselenides for highly selective asymmetricintramolecular selenocyclisation

Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols aci d alkenyl urethanes using chiral 2-[1(dimethylamino)ethyl]ferrocenylselenen yl cations proceeds smoothly to give the corresponding organoselenenyl moie ty-containing lactones, cyclic ethers and N-heterocycles, respectively, in good to excellent chemical yields (up to 97%) with very high diastereoselec tivities (up to 98% de). The nature of the counter anions of the selenenyla ting agents affected remarkably the diastereoselectivity of the cyclisation , PF6- and BF4- being revealed to be the best for alkenoic acids and alkeno ls, and alkenyl urethanes, respectively A plausible reaction scheme for the cyclisation is presented where a chiral selenenylating agent approaches th e carbon-carbon double bond of the substrate from the less sterically-conge sted direction to afford a chiral episelenonium ion followed by an intramol ecular back side attack of a nucleophile.