Lanthanide-catalyzed asymmetric 1,3-dipolar cycloaddition of nitrones to alkenes using 3,3′-bis(2-oxazolyl)-1,1′-bi-2-naphthol (BINOL-Box) ligands

• Published in: Journal of organometallic chemistry 2000-05, Vol.603 (1), p.6-12
• Main Authors: Kodama, Hidehiko, Ito, Junji, Hori, Kazushige, Ohta, Tetsuo, Furukawa, Isao
• Format: Article
• Language: English
• Subjects: 1,3-Dipolar; 3,3′-bis(2-oxazolyl)-1,1′-bi-2-naphthols; Isoxazolidine; Lanthanide catalysis
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/S0022-328X(00)00024-3

New BINOL-derived ligands, 3,3′-bis(2-oxazolyl)-1,1′-bi-2-naphthols (BINOL-Box), bearing chiral bis-oxazoline at the 3,3′-carbons, were synthesized from commercially available 1,1′-bi-2-naphthol (BINOL). With the new ligands obtained, we found that asymmetric 1,3-dipolar cycloaddition reaction of N-benzylidenebenzylamine N-oxide ( 2) to 3-(( E)-2-butenoyl)-1,3-oxazolidin-2-one ( 1) was catalyzed by BINOL-Box–scandium complexes to give isoxazolidine 3 in high yield with high diastereo- and enantioselectivity. For example, the reaction of 1 with 2 catalyzed by a 6 mol% ( S, R)- 7d and 5 mol% Sc(OTf) 3 complex proceeded to give the endo-3 as the major diastereomer with an endo: exo ratio of 97:3 and 87% ee of the endo-product in the presence of 4 Å molecular sieves. Interestingly, the absolute configuration of the major product was changed according to the kind of additive used.