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.