Jensen, K. B.; Gothelf, K. V.; Jørgensen, K. A.
Helv. Chim. Acta 1997, 80, 2039–2046, doi: 10.1002/hlca.19970800704
Department of Chemistry, Aarhus University, DK-8000 Aarhus C
Catalytic control of regio-, diastereo-, and enantioselectivity in the 1,3-dipolar cycloaddition of 3-acryl-oyloxazolidin-2-one (4) with different nitrones 2 by the application of a [TiX2(TADDOLato)] complex as the catalyst was developed (TADDOL = α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol). In the absence of a catalyst, the 1,3-dipolar cycloaddition of 4 with 2 proceeded to give a mixture of regioisomers, whereas, in the presence of a catalyst, the regioselectivity of the reaction could be controlled. Three asymmetric [TiX2(TADDOLato)] catalysts were tested, and it was found that use of the [Ti(OTs)2(TADDOLato)] complex gave complete regioselectivity, high ‘endo’-selectivities (> 90% d.e.), and enantioselectivities corresponding to 48–70% e.e.