Cinchona-Alkaloids Based Isoselenazolones: Synthesis and Their Catalytic Reactivity in Asymmetric Bromolactonization of Alkenoic Acid

摘要

Abstract A series of chiral isoselenazolones have been synthesized and characterized by multinuclear ( 1 H, 13 C, and 77 Se) NMR, mass spectrometry, and single crystal X-ray crystallography. Catalytic reactivity of synthesized chiral isoselenazolones was studied in the enantioselective bromolactonization of alkenoic acids using N -bromosuccinimide as a source of bromine. A series of alkenoic acid underwent bromolactonization successfully in the presence of 10?mol% of chiral isoselenazolone catalyst and excellent yields of bromolactones were obtained with high diastereoselectivity and moderate enantioselectivity. Isoselenazolone catalyst derived from quininamine afforded bromolactones in 82–94?% yield with 1?47?% enantioselectivity while rest of the isoselenazolones derived from simple chiral ( S )-phenylethyl, and ( S )-naphthylethyl, quinidin, and cinchonidin-amine afforded poor enantioselectivity in the bromolactonization reaction. Furthermore, isoselenazolone having Se–N bond gave best enantioselectivity in the bromolactonization of 5-phenyl-4-pentenoic acid as compared to the isothiazolone having S–N bond. Also isoselenazolone gave best enantioselectivity than the corresponding methyl selenide and diselenide bearing the same quininamine auxiliary in the organoselenium catalyst. Crystal structure and enantioselectivity outcome in bromolactonization on similar isoselenazolone catalysts; quininamine based (intramolecular Se…N distance 3.56??, ee 47?%); cinchonidinamine based (Se…N distances 3.80 ?, ee 17?%), and 7-methyl-amide and quininamine based (Se…N distances 3.72 ?, ee 28?%) suggests that intramolecular Se…N interaction could be the crucial parameter for the enantioselectivity outcome of the reaction.