The use of chiral diferrocenyl diselenides for highly selective asymmetric intramolecular selenocyclisation
Abstract
Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral 2-[1-(dimethylamino)ethyl]ferrocenylselenenyl cations proceeds smoothly to give the corresponding organoselenenyl moiety-containing lactones, cyclic ethers and N-heterocycles, respectively, in good to excellent chemical yields (up to 97%) with very high diastereoselectivities (up to 98% de). The nature of the counter anions of the selenenylating agents affected remarkably the diastereoselectivity of the cyclisation, PF6– and BF4– being revealed to be the best for alkenoic acids and alkenols, and alkenyl urethanes, respectively. A plausible reaction scheme for the cyclisation is presented where a chiral selenenylating agent approaches the carbon–carbon double bond of the substrate from the less sterically-congested direction to afford a chiral episelenonium ion followed by an intramolecular back side attack of a nucleophile.